RPM relay?

[penciltester]

Guys this is my line of thought, please correct if i'm off base.

If the pump kicks on when the key is turned then the rpm relay must be functioning, correct? This is the case with our new SpecialT pump. Pump kicks on but fuel is not reaching the engine. The individual I am purchasing the car from thinks it may be a relay but if the pump is turning on then aren't the relays fine? And it wouldn't be the inertia switch because that would keep the pump from kicking on at all.

If that's the case then aren't we looking at another bad pump or a clog/kink/cockroach in the fuel line between the pump and the accumulator? It's the last line to check.

Oh and he drained and cleaned the tank, so I don't think it's a clogged fuel pump.

And SpecialTAuto got the pump to us within a week, pleasantly surprised.

Any other ideas?

Thanks

[David T]

Maybe the feed and return fuel lines got mixed up? That would cause the pump to run but the motor won't get any fuel. It is also possible the pick-up line is kinked or maybe there just isn't enough fuel in the tank.

[penciltester]

Didn't think about the lines being switched around, i'm going to laugh if thats it.

Forgot to ask a question, might be a stupid question. Does the fuel pump run continuously once activated, or does it stop if there is enough pressure in the line?

[Tillsy]

Didn't think about the lines being switched around, i'm going to laugh if thats it.

Forgot to ask a question, might be a stupid question. Does the fuel pump run continuously once activated, or does it stop if there is enough pressure in the line?

Just a few moments to pressurise - give or take some randomness if you have the OEM relay ;)

[NightFlyer]

Didn't think about the lines being switched around, i'm going to laugh if thats it.

Forgot to ask a question, might be a stupid question. Does the fuel pump run continuously once activated, or does it stop if there is enough pressure in the line?

I'm not sure if I'm right about this or not, but I believe that the pump only primes the fuel system when the key is turned to the run position (engine not running), which provides enough fuel for the CSV to do its thing in getting the engine started from cold, or enough fuel to start the engine when warm without CSV assistance. Once running, the tach signal keeps the relay closed and the pump running constantly, hence where the relay's name derives from.

I could be wrong though, so don't quote me.

[Rich]

If the pump kicks on when the key is turned then the rpm relay must be functioning, correct? This is the case with our new SpecialT pump. Pump kicks on but fuel is not reaching the engine. The individual I am purchasing the car from thinks it may be a relay but if the pump is turning on then aren't the relays fine? And it wouldn't be the inertia switch because that would keep the pump from kicking on at all.


Q: What tells you that fuel is not reaching the engine?

[Bitsyncmaster]

Yes the fuel pump runs continuously when the engine is running. The return line allows the excess "pumping" back to the tank. Some RPM relays don't prime in some cars but as soon as you start cranking the engine the pump starts running.

[penciltester]

Thanks everybody.

We know that fuel is not reaching the engine because we disconnected the line running into the fuel filter, cranked the engine, checked to make sure the pump was running and nothing came out the line.

I have no problem with the guy buying new relays for the car and pray that fixes it but if there is a different fix ,one where he isn't spending more money, I would be happy.

Another question: If the lines running from the pump are switched around, is there anyway fuel would get to the engine?

[OverlandMan]

Thanks everybody.

We know that fuel is not reaching the engine because we disconnected the line running into the fuel filter, cranked the engine, checked to make sure the pump was running and nothing came out the line.

I have no problem with the guy buying new relays for the car and pray that fixes it but if there is a different fix ,one where he isn't spending more money, I would be happy.

Another question: If the lines running from the pump are switched around, is there anyway fuel would get to the engine?

If it were me, I would start at the pump and work my way back until I found the culprit. A power probe and/or a rigged up RPM relay toggle would probably work best for testing. Here's a pic of one I rigged up for fuel-flow testing my injectors last weekend.

http://dmctx.blogspot.com/2014/05/fuel-flow-testing.html

[Rich]

We know that fuel is not reaching the engine because we disconnected the line running into the fuel filter, cranked the engine, checked to make sure the pump was running and nothing came out the line....

Another question: If the lines running from the pump are switched around, is there anyway fuel would get to the engine?

Good, thanks for that no-fuel-flow detail.

Agreeing with the previous post - time to work back to the pump after some initial checks.

Some questions since we know the pump runs (or at least makes noise when powered) and we think fuel is not getting to the filter:

a. Are you sure you checked the correct fuel line and it was indeed at the fuel filter inlet port?
b. Are you sure there is enough fuel in the tank?
c. Have you jumped the RPM relay, engine off, so the pump can run longer than the initial prime or cranking? Get a jar for the fuel and run it for 15-30sec. Still nothing at all? Then work back closer to the pump. You are looking for a plumbing problem.
d. And the other reason to do relay bypass test: Does the pump see at least 11.5V across its +/- connectors when it is running?

And, no, if the pump output isn't connected to the main fuel feed line then the K-Jet won't work.

[penciltester]

A.He unhooked the hard line from the filter.

B.There is a good 2 to 3 inches standing in the tank.

C.Have not jumpered the relay to my knowledge. Will take Overlandman's approach, hopefully this weekend.

D. Will check.

I will also have him crank the engine for a bit to make sure the pump is running the whole time, just for my own peace of mind.

And now for another question. When I'm looking at the pump which hose is the the return and which is the feed? When/if I go to his garage I would like to rule out hose mixup immediately.

Thanks everybody for all the help and answering a noobs questions.

[Rich_NYS]

This is a pic of my fuel pump when I replaced the hoses. I'm a new owner also, so I don't know if there are any variations to watch out for (someone please confirm my info.)

The pump feed is coming off the pump hardware in the center, the return is the barb fitting that connects into the rubber part.

On my car, the hardline closest to the pump is the one the feed connected to. Also, there's an accumulator midway between this area and the rear of the car; I don't know if that can be related to your issue, but it's good to be aware of as you become familiar with the car (you'll hear it referred to often.)

27674

[Rich]

Answers and suggestions inserted in bold:



A.He unhooked the hard line from the filter. If you mean you are checking at the outlet of the filter then add "clogged filter" to list of potential problems. You need to check for fuel flow closer to the tank/pump since we know there is no delivery way back there.

B.There is a good 2 to 3 inches standing in the tank. Add a couple of gallons - then you can rule out low-fuel as a cause. And since you have access to the pump for viewing into the tank are you sure the pump inlet is not kinked?

C.Have not jumpered the relay to my knowledge. Will take Overlandman's approach, hopefully this weekend. Good

D. Will check. Good.

I will also have him crank the engine for a bit to make sure the pump is running the whole time, just for my own peace of mind. Good, but remember that "pump running" is not the same as "pump running correctly", it's just a data point.

And now for another question. When I'm looking at the pump which hose is the the return and which is the feed? When/if I go to his garage I would like to rule out hose mixup immediately. As per Rich NYS there is only one pump-hose connection, the one in the center. The bottom of the pump is the inlet

[DMCMW Dave]

And, no, if the pump output isn't connected to the main fuel feed line then the K-Jet won't work.

I've seen a car run with the pump hooked up backwards. Not well, but it will run.

We also had a car in here where the (prior owner?) hooked up the pump backwards. To fix it, he reversed the connections at the fuel distributor.

This of course put the accumulator in the return line and ran the fuel backwards through the filter causing an resistance in the return line and no accumulator function in the pressure line. The car ran well enough to drive in!

[jawn101]

To fix it, he reversed the connections at the fuel distributor.

That might actually be the most ridiculous thing I've ever heard :lol:

[Flash66]

I installed mine backwards and it barely ran.


Sent from my iPad using Tapatalk

[penciltester]

Hi guys thanks for all the suggestions. I ended up having the car hauled to my house to finish the work. Oddly enough after the relays had a few good taps it started running. Have no idea why that worked but then some other odd electrical things sprung up. But I will start a separate post for those oddities.

Thanks again everybody!