Hot start problem resolved due to failed check valve in the DMCH fuel pump

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Originally Posted by NightFlyer

1) PLEASE - install an external inline check valve. Trust me, you'll be glad that you did. It's $18 and all of 20 minutes of time. It's definitely worth it IMHO!

2) When you installed the pump, are you sure that you had the bottom of the pump as close to touching the bottom of the tank as possible? The unit, as you probably know, is spring loaded and isn't very smooth in it's action when decompressing after being compressed (it's easy to get it stuck in a compressed state). It also doesn't fit the tank when fully decompressed, thus some level of compression is necessary. I test fit mine about 4 times before I was able to get it where the bottom of the pump was just barely off the bottom of the tank. I've only been running mine for the last 3 months and about 4,000 miles, but have always run it down low enough to trip the low fuel light. No issues such as those you've described thus far.

That's about the only thing that I can think of.

You may also want to check the RPM relay - if that's opening/closing while you're driving, it could potentially cause what you're describing as it's stopping and re-engaging the pump.

Best of luck!

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Yes, an external check valve is on the list for the rainy season when it starts in a month or so. Peace of mind is worth everything to me.

I don't actually know for sure about the pump being compressed fully. That might be a factor, but would the gauge be off if it wasn't fully compressed in the tank? Or is the float attached at the top? I can't remember.

RPM relay is already Dave's solid state one and works fine under all circumstances - this issue only crops up when the tank drops low-ish.

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Originally Posted by jawn101

Yes, an external check valve is on the list for the rainy season when it starts in a month or so. Peace of mind is worth everything to me.

I don't actually know for sure about the pump being compressed fully. That might be a factor, but would the gauge be off if it wasn't fully compressed in the tank? Or is the float attached at the top? I can't remember.

RPM relay is already Dave's solid state one and works fine under all circumstances - this issue only crops up when the tank drops low-ish.

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If I'm recalling correctly, the float is attached near the middle of the pump body. However, the arm is long and contains a near 90 degree bend, thus allowing it to extend above the top and below the bottom of the pump. So, the float will still read properly even if the pump is over-compressed in the installation.

Remember, you want the pump as fully DE-compressed as possible in the installation.

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Originally Posted by NightFlyer

If I'm recalling correctly, the float is attached near the middle of the pump body. However, the arm is long and contains a near 90 degree bend, thus allowing it to extend above the top and below the bottom of the pump. So, the float will still read properly even if the pump is over-compressed in the installation.

Remember, you want the pump as fully DE-compressed as possible in the installation.

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OK, the mount/pivot point is actually towards the top, but the angle of the rod is a full 90 degrees. Recalling my pump, I distinctly remember the float bottoming just slightly below the bottom of the pump.

I'd also check for cracks in the plastic housing - maybe air is being introduced that way...???

https://store.delorean.com/images/Pr...arge/10569.jpg

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Originally Posted by NightFlyer

OK, the mount/pivot point is actually towards the top, but the angle of the rod is a full 90 degrees. Recalling my pump, I distinctly remember the float bottoming just slightly below the bottom of the pump.

I'd also check for cracks in the plastic housing - maybe air is being introduced that way...???

https://store.delorean.com/images/Pr...arge/10569.jpg

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Interesting. So I should remove the pump assembly and make sure it's fully extended to the bottom of the tank. That makes sense, but I'm not looking forward to it. Maybe I'll do it when I splice in that check valve.

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Originally Posted by DeLorean03

I am considering re-installing John's power pump setup and seeing what happens. I'm getting a bit tired of this situation. I will prolly do that over the weekend and let everyone know my status if it changes anything.

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I'm curious as to whether or not you tried this yet, and if so, what the results were...

Today I installed the check valve in my fuel line. I had an on and off hot start issue and I figured what the heck the valve can't hurt. For anyone on the fence with this, hey the cost was around $15 and it took me around 15 minutes to put it in.
Andy B 03513

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Originally Posted by NightFlyer

I'm curious as to whether or not you tried this yet, and if so, what the results were...

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Didn't get to it. Here's why. I have unhooked my CSV, and ever since then, my car fires nearly flawlessly all the time. It's something in the cold start system, and since Eddie is about to fix that permanently, I said "heck with it".

Car heads to him a week from Monday, and it's 55 here for the high, so yeah, the days of driving the DeLorean for 2013 are pretty much over.

Ok, so I got mine taken care of. I TRIED to order the Viton check valve from US Plastics and it was taking FOREVER to them to get them back in stock. So I went with the same check valve but with Buna-N instead since they had those. And of course, about 3 days after I order the Buna-N, they get the Viton back in stock. :facepalm:

So I installed it and yes, super easy to do. But I still had my hot start problem. After researching it, I know that lack of rest pressure is really only due to three things under most circumstances:

1) Fuel pump check valve
2) Accumulator
3) PPR O-Rings

Since the PPR O-rings were the path of least resistance at this point, I went there first. I had some that I bought from Hervey :nervous: about 6 months ago and put them in last night. Another 15 min job, if that. I was a little nervous when I got the old o-rings out because there wasn't anything obviously wrong with them. Once I took the old small o-ring off and put it next to the new small o-ring, the old one was noticeably larger than the new one. That was the only difference. But Hervey's new o-rings were a perfect, snug fit (thankfully and with intense relief) and I didn't have any problems getting them back in and damaging them along the way. I put a very light coat of silicone paste on the o-rings to help facilitate sliding everything back in, just in case.

And that was it. The DeLorean starts up just as fast as my 2013 Passat, whether hot or cold.

Doc Brown in reference to the PPR O-rings: "Unbelievable that this little piece of junk could be such a big problem".


Thanks for the help!

Yes, you definitely have to use lubricant before sliding in.

Buna-N will swell with todays gas. Look at that O-ring after it sits out on the bench awhile. It should get smaller. I did a swell test measurement back on the old .com forum but don't have a copy of my results.

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Originally Posted by Bitsyncmaster

Buna-N will swell with todays gas. Look at that O-ring after it sits out on the bench awhile. It should get smaller. I did a swell test measurement back on the old .com forum but don't have a copy of my results.

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Interesting. That might be why my old o-ring was noticeably larger. I did a lot of research on the material and it said it was compatible with gasoline. What other applications would Buna-N be used for?

I still have a Viton check valve on the way so I'll probably just swap it out and be done with it. Any idea how long it takes for Buna-N to deform?

Who has a good source for Viton o-rings for the PPR?

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Originally Posted by opethmike

Yes, you definitely have to use lubricant before sliding in.

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Yep, that's what she said...

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Originally Posted by kings1527

Interesting. That might be why my old o-ring was noticeably larger. I did a lot of research on the material and it said it was compatible with gasoline. What other applications would Buna-N be used for?

I still have a Viton check valve on the way so I'll probably just swap it out and be done with it. Any idea how long it takes for Buna-N to deform?

Who has a good source for Viton o-rings for the PPR?

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This is where I get mine:
http://www.mcmaster.com/#metric-o-rings/=p3nifs

I use 1.9 mm X 3.8 mm but I think the stock size is 2.0 mm X 4.0 mm. Either works but I guess the smaller one gets more seal since it has less surface area. Viton is a little harder then Buna-N.

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Originally Posted by Bitsyncmaster

This is where I get mine:
http://www.mcmaster.com/#metric-o-rings/=p3nifs

I use 1.9 mm X 3.8 mm but I think the stock size is 2.0 mm X 4.0 mm. Either works but I guess the smaller one gets more seal since it has less surface area. Viton is a little harder then Buna-N.

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I fail to see how a smaller one gets MORE seal with LESS surface area. :hmm:

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Originally Posted by DMC5180

I fail to see how a smaller one gets MORE seal with LESS surface area. :hmm:

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Constant pressure to less surface area will compress the o-ring more than a larger surface area.

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Originally Posted by Bitsyncmaster

This is where I get mine:
http://www.mcmaster.com/#metric-o-rings/=p3nifs

I use 1.9 mm X 3.8 mm but I think the stock size is 2.0 mm X 4.0 mm. Either works but I guess the smaller one gets more seal since it has less surface area. Viton is a little harder then Buna-N.

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Thanks perfect, thanks for the info Dave. So that'll be the size for the smaller o-ring. Do we know the size for the bigger o-ring? Or does that one prove to not be much of a factor for holding rest pressure when compared to the smaller o-ring?

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Originally Posted by kings1527

Thanks perfect, thanks for the info Dave. So that'll be the size for the smaller o-ring. Do we know the size for the bigger o-ring? Or does that one prove to not be much of a factor for holding rest pressure when compared to the smaller o-ring?

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Don't worry about the larger O-ring. It really stays dry and does not need to seal.

Quote:

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Originally Posted by kings1527

Ok, so I got mine taken care of. I TRIED to order the Viton check valve from US Plastics and it was taking FOREVER to them to get them back in stock. So I went with the same check valve but with Buna-N instead since they had those. And of course, about 3 days after I order the Buna-N, they get the Viton back in stock. :facepalm:

So I installed it and yes, super easy to do. But I still had my hot start problem. After researching it, I know that lack of rest pressure is really only due to three things under most circumstances:

1) Fuel pump check valve
2) Accumulator
3) PPR O-Rings

Since the PPR O-rings were the path of least resistance at this point, I went there first. I had some that I bought from Hervey :nervous: about 6 months ago and put them in last night. Another 15 min job, if that. I was a little nervous when I got the old o-rings out because there wasn't anything obviously wrong with them. Once I took the old small o-ring off and put it next to the new small o-ring, the old one was noticeably larger than the new one. That was the only difference. But Hervey's new o-rings were a perfect, snug fit (thankfully and with intense relief) and I didn't have any problems getting them back in and damaging them along the way. I put a very light coat of silicone paste on the o-rings to help facilitate sliding everything back in, just in case.

And that was it. The DeLorean starts up just as fast as my 2013 Passat, whether hot or cold.

Doc Brown in reference to the PPR O-rings: "Unbelievable that this little piece of junk could be such a big problem".


Thanks for the help!

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Glad to hear that you were finally able to figure out the problem! It's great to finally have a car that you know will start every time, isn't it?

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Originally Posted by Bitsyncmaster

Don't worry about the larger O-ring. It really stays dry and does not need to seal.

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Great, thanks Dave.

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Originally Posted by NightFlyer

Glad to hear that you were finally able to figure out the problem! It's great to finally have a car that you know will start every time, isn't it?

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There's hardly anything worse than trying to start the car and nothing's happening! And it always happens in front of a group of people. Then you're just waiting for the jokes to start flying.... :)

It'll be nice to get the Viton check valve and PPR o-ring in place and be done!

So for anyone who's interested, it's been about two months since I put a regular (assuming) Buna-N o-ring in my PPR plunger and my car just started doing the same thing as I described earlier. So I guess one could say the average life span before Buna-N will deform is about two months. Dastardly ethanol.

Today I installed the nitrile o-ring with the size Dave M mentioned and I'll report back if there are any problems. If I pass the two month mark, I'll take it as a good sign.

What were the original o-rings made out of? Mine is original and I pump the cheapest gas I can find. Buna rubber o-rings are considered to have excellent compatibility with ethanol for both static and dynamic applications. Basically, the same compatibility as viton.

-Bob

My terminology is mixed up. You're right. Viton (not nitrile) is the stuff that's been widely regarded in the forum to have the best compatibility with ethanol. Buna-N supposedly still has problems. As to what the originals were made of, I'm not sure but I'm guessing they held up better back in the day due to the fact that ethanol hadn't been introduced yet.

Buna-N is NOT ethanol resistant - it will deteriorate when exposed to ethanol of any concentration - higher concentrations will cause faster wear.

Viton has been independently tested to be impervious to ethanol concentrations as high as 15%, although DuPont claims it can handle much higher concentrations without issue.

Buna-N is absolutely compatible with ethanol, in concentrations as high as they get (don't get me started on azeotropes).

Every o-ring manufacturer out there lists this and Buna-N (nitrile) is the recommended material for sealing with o-rings for ethanol.

Actually from what I'm reading, Viton is actually a poor choice for ethanol. It's marginal at best.

Simply put, if Buna-N o-rings are deteriorating because of modern fuels, it is most definitely NOT because of the ethanol in them.

-Bob

It's a good question about original O-rings. My guess is they are Buna-N but maybe were a smaller size. I tested Buna and Viton side by side soaking in ethanol gas. The Buna expanded quite a bit and the Viton did not change at all. So if my guess is correct, the smaller size keeps Buna-N working.

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Originally Posted by rdarlington

Actually from what I'm reading, Viton is actually a poor choice for ethanol. It's marginal at best.

Simply put, if Buna-N o-rings are deteriorating because of modern fuels, it is most definitely NOT because of the ethanol in them.

-Bob

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Not sure where you're reading about Viton being a poor choice for ethanol but that's not right. It's not so much a matter of deterioration, but rather swelling resulting in deformity. That's why the PPR o-ring starts having problems. It becomes malformed and can't hold rest pressure. I've personally (as have others) seen a nice swollen buna-n o-ring from ethanol based fuel.

In short, go with Viton unless you want to look cool working on your car all the time.

And a special thanks to Dave M for all of his research and info on this.

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Originally Posted by kings1527

Not sure where you're reading about Viton being a poor choice for ethanol but that's not right. It's not so much a matter of deterioration, but rather swelling resulting in deformity. That's why the PPR o-ring starts having problems. It becomes malformed and can't hold rest pressure. I've personally (as have others) seen a nice swollen buna-n o-ring from ethanol based fuel.

In short, go with Viton unless you want to look cool working on your car all the time.

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http://www.sterlitech.com/oring-compatibility-chart


I see viton listed all over the map for both gasoline and ethanol.

One thing I see that's consistent is Buna-N for both gasoline and ethanol resistance. It is *the* recommended material for both. Who is manufacturing your o-rings? Are you sure you're getting what you're paying for?

Just an FYI, I have extensive experience in the vacuum technology and industrial chemistry world and deal with chemical compatibility for these types of seals for both terrestrial and space applications. What I think is that you guys are picking up 3rd rate o-rings and are making assumptions. The available data out there from the manufacturers and industry publications suggest that Buna-N is the stuff you want for o-rings for cars. They've been using ethanol in gasoline since the 1920s (granted, the o-ring didn't exist in the 1920s) and is not new.

There are plenty of reasons to go with viton, but I don't think I know of any where it comes to dealing with cars.

-Bob

Deteriorate wasn't the best word to use - should have been 'compromised' instead.

Whether it's being caused by the ethanol or something else, fact remains that Buna-N is compromised by today's standard fuel blends, whereas Viton is not. Dave M's side by side is consistent with the results of other comparison tests that I've seen. Alex's recent personal experience would also seem to validate/support the concerns about using Buna-N in applications on our cars.

While the choice is yours to make, I can personally attest to the fact that I haven't encountered any issues running Viton rubber in the fuel system components on my car.

The difference in price between the two materials is marginal/nominal at best...

It only takes about a one or two hour soak in gasohol if you have some calipers to do the test I did.

Measure each before you soak, Tag which is which, soak and remeasure. I would like another verify of what you find.

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Originally Posted by Bitsyncmaster

It only takes about a one or two hour soak in gasohol if you have some calipers to do the test I did.

Measure each before you soak, Tag which is which, soak and remeasure. I would like another verify of what you find.

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The problem is we really do not know exactly what the originals were made of. What they sell today and call Buna N is probably not what they used to make. Whatever the originals were made of, it seemed to be OK. The problems seem to start once you change them. There are plenty of mixture units out there with the original "O" rings in them and they function just fine. If you should replace them I would suggest you try to use Viton of the correct size since what they pass off as Buna N is not going to work. I believe one of the problems is that the Buna N swells and since this is a dynamic seal (the "O" rings are on parts that move) when it swells it gets chopped as it moves over the slots. If it was just used to seal a part that doesn't move (like a drain plug) where it is captured and cannot swell, Buna N seems to be fine.

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Originally Posted by rdarlington

There are plenty of reasons to go with viton, but I don't think I know of any where it comes to dealing with cars.

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...Automatic transmission o-rings and seals.

...I used a Viton o-ring from rebuilt kit leftovers and have had no problems for years.
Back when Dave first posted measurement/results, I had very similar results.

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Originally Posted by NightFlyer

1) PLEASE - install an external inline check valve. Trust me, you'll be glad that you did. It's $18 and all of 20 minutes of time. It's definitely worth it IMHO!

2) When you installed the pump, are you sure that you had the bottom of the pump as close to touching the bottom of the tank as possible? The unit, as you probably know, is spring loaded and isn't very smooth in it's action when decompressing after being compressed (it's easy to get it stuck in a compressed state). It also doesn't fit the tank when fully decompressed, thus some level of compression is necessary. I test fit mine about 4 times before I was able to get it where the bottom of the pump was just barely off the bottom of the tank. I've only been running mine for the last 3 months and about 4,000 miles, but have always run it down low enough to trip the low fuel light. No issues such as those you've described thus far.

That's about the only thing that I can think of.

You may also want to check the RPM relay - if that's opening/closing while you're driving, it could potentially cause what you're describing as it's stopping and re-engaging the pump.

Best of luck!

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Hey - this is a little late for a follow up, but that's how long it took me to run the fuel tank down low enough to inspect. I just pulled the blanking plug off the level sender hole and inspected the pump. It is fully extended and resting on the bottom of the tank. There is about 1/4" of fuel surrounding the baffle area (that is to say that the baffle is about 1/4" submerged) and the gauge is reading a tick below 1/4 full. But I still have the "collapsed pickup hose" symptoms under hard acceleration when the tank is this low.

Anyone have any other ideas what could be causing this? Dave S, are you still out there reading this thread? :)

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Originally Posted by jawn101

Hey - this is a little late for a follow up, but that's how long it took me to run the fuel tank down low enough to inspect. I just pulled the blanking plug off the level sender hole and inspected the pump. It is fully extended and resting on the bottom of the tank. There is about 1/4" of fuel surrounding the baffle area (that is to say that the baffle is about 1/4" submerged) and the gauge is reading a tick below 1/4 full. But I still have the "collapsed pickup hose" symptoms under hard acceleration when the tank is this low.

Anyone have any other ideas what could be causing this? Dave S, are you still out there reading this thread? :)

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Sounds like a crack somewhere within the assembly is introducing air into the system when the fuel level gets low enough. Is the pump still under warranty?

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Originally Posted by NightFlyer

Sounds like a crack somewhere within the assembly is introducing air into the system when the fuel level gets low enough. Is the pump still under warranty?

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Probably not. I'd have to pull the whole assembly to check for one.

FWIW, I did measure the fuel levels in the tank and it seems like there is more around 1" of fuel down there. Perspective made it tough to estimate properly, and I had a hard time getting a real measurement as the fuel mostly evaporated off my rulers before I could get them into the light to read.

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Originally Posted by jawn101

Probably not. I'd have to pull the whole assembly to check for one.

FWIW, I did measure the fuel levels in the tank and it seems like there is more around 1" of fuel down there. Perspective made it tough to estimate properly, and I had a hard time getting a real measurement as the fuel mostly evaporated off my rulers before I could get them into the light to read.

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I would think that an inch should be enough fuel to still operate the pump normally, but then again, I really don't have any basis of comparison / experience. It's possible that the sender float is incorrectly adjusted and giving an incorrect reading on the dash gauge.

One way to check would be to siphon the remaining fuel in the tank into something that you can use to measure the amount of fuel actually present and compare it to what the gauge is reporting. You can siphon via the sender hole. Inclining the car (by parking on a steep incline or jacking it up) will concentrate the remaining fuel into either the front or back of the tank where you can effectively siphon a vast majority of the remaining fuel out (only a nominal/insignificant amount will remain). Remember that the tank's capacity is 13.2 gallons, thus if your gauge is reading 1/4 tank, you should have roughly 3.3 gallons of fuel remaining within the tank. If the gauge is close to what your measured results yield, then you'll know for certain that the problem lies in the pump housing, unfortunately...

Again, best of luck!

Quote:

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Originally Posted by NightFlyer

I would think that an inch should be enough fuel to still operate the pump normally, but then again, I really don't have any basis of comparison / experience. It's possible that the sender float is incorrectly adjusted and giving an incorrect reading on the dash gauge.

One way to check would be to siphon the remaining fuel in the tank into something that you can use to measure the amount of fuel actually present and compare it to what the gauge is reporting. You can siphon via the sender hole. Inclining the car (by parking on a steep incline or jacking it up) will concentrate the remaining fuel into either the front or back of the tank where you can effectively siphon a vast majority of the remaining fuel out (only a nominal/insignificant amount will remain). Remember that the tank's capacity is 13.2 gallons, thus if your gauge is reading 1/4 tank, you should have roughly 3.3 gallons of fuel remaining within the tank. If the gauge is close to what your measured results yield, then you'll know for certain that the problem lies in the pump housing, unfortunately...

Again, best of luck!

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You really cannot properly inspect the baffle assembly from the sender unit hole. Pull the pump out and inspect the pick-up hose. If is is swollen or soft either put a spring in it or replace it.

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Originally Posted by David T

You really cannot properly inspect the baffle assembly from the sender unit hole. Pull the pump out and inspect the pick-up hose. If is is swollen or soft either put a spring in it or replace it.

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David,

Jon has the NEW DMCH Pump combo unit. No Pickup hose on this one.

OK, after trading some emails, photos, videos and some call time with Dave S (have I mentioned lately how great he is?) I've got a plan of action.

First step was to test the level sender. I held the float down gently with this threaded rod:

http://dmctalk.org/attachment.php?at...8&d=1390256908

Then verified that the sender and low fuel light were working properly

http://dmctalk.org/attachment.php?at...9&d=1390256911

OK, that's all fine. On to the next step - running the engine with the sender plug removed to observe the pump operation.

https://www.youtube.com/watch?v=ACfkTwB4AJc

Um. Well, I'm pretty sure that isn't supposed to happen. Next step was to remove and inspect the pump assembly for leaks/cracks:

http://dmctalk.org/attachment.php?at...0&d=1390256918

http://dmctalk.org/attachment.php?at...1&d=1390256925

http://dmctalk.org/attachment.php?at...2&d=1390256933

http://dmctalk.org/attachment.php?at...3&d=1390256939

Clean as a whistle and no obvious cracks/splits or anything concerning. So, I tried reinstalling the assembly. It's a DeLorean after all, sometimes a simple R&R is all it takes to fix a problem, right?

Wrong. Same symptoms after reinstalling. So I pulled the pump up out of the tank just enough to observe it in operation from directly above instead of from the side. Here's what I saw:

https://www.youtube.com/watch?v=3bKBobEnZos (sorry, can only embed 1 video per post for some reason?)

Uh oh. The leak is right at the top of the pump itself.

So right now the working theory is that the pump was still providing adequate pressure to the engine (no issues at all with running or driveability unless the gas is very low) but due to this leak, the fuel in the baffle was being depleted very quickly - causing the poor running conditions with low fuel in the tank.

Long and short of it is that 2100 is off the road while the pump assembly heads back to DMCMW for a thorough check and repair by Dave. A bummer but at least it's a resolution!

Will update again when I have more info on the situation.

BTW: Dave said he was going to return the unit with an inline check valve supplied.

Great job documenting this. That is surprising to see gas leaking out the top of the unit! No wonder it was so hard to track down.