Melted number seven fuse Fuel pump

[JIMJAM]

Hi guys, been a troublefree summer till today. Got lucky though. The car while idleing cut off in my garage.:huh:. Would not start,no fuel pump sound. Did the voltage test and none at the pump. The PO had run another line to a fuse holder. The fuse holder was melted really good. Unusable,fuse was destroyed and I could not even get the pieces out. Reason he ran that line is the number 7 slot on the panel is a big melted hole. So this has happened before which bothers me.
I will not be able to replace the fuse/holder until tonight or the morning.
I do not know if this solves the issue but here is a question ahead of time.
What could or does cause the number 7 seven fuse to melt? I had a 20 in there.
Since it appears to have happen to the po, I want to know so I can fix it.
BTW- Fuel pump- One of Johns Super pumps, less than 1000 miles. Most things related to fuel has been replaced.
Thanks for any tips,info and general postive uplifting replies.:p

[Farrar]

Do you have a good ground at the pump? There has been some concern in the community recently about poor grounding causing voltage drop.

Farrar

[Bitsyncmaster]

I've found John's Power pump draws about 10 amp and the standard pump about 7 amps. But that fuse also powers the WUR heater. That heater current is less than one amp but if you get the infamous short circuit inside the WUR that would cause the fuse to overheat. I don't know why the fuse does not blow when that happens. Hence my recommended fusing of the WUR.

There is a small gauge wire for the load side of the fuse. That will add to the problem but as long as the connection is solid it should not cause it.

It may just be the fuel pump current changes and then the fuse would be running near the max rating. But I have seen any higher currents with my testing.

[JIMJAM]

O boy, here we go with these grounds again :swear1:
Is this where they meet at the area just right of the water bottle, up in that area under the hood? If so I have been there many times and done the usual cleaning.
I did noticed the wire that the fuse was added to feel/looks old. Its that old brown copper look with not much flex. Probably wouild not hurt to replace it.
But lets start simple. Tell me where the ground wire is and I will track it down and make sure its got a good clean contact.
Btw- Hi

Edit- What???? Another infamous Delorean short or Gremlin!! Say it aint so. Tell ya I think I have experienced every infamous, notorious, gremlin there is. Trying to remeber the last one we tracked down and fixed togther. Something electrical Im sure.

[Farrar]

In my case, I wouldn't bother cleaning the grounds; I'd simply run a new one to the frame from the pump.

Dave has a good point; if the CPR has a short, that would cause the problem.

Farrar

[sean]

In my case, I wouldn't bother cleaning the grounds; I'd simply run a new one to the frame from the pump.


That would bypass the inertia switch, a safety feature that should probably stick around.

[Farrar]

That would bypass the inertia switch, a safety feature that should probably stick around.

Good point; but as a temporary measure for troubleshooting I would still try it. Jim's grounds should be perfectly clean by now. I think he cleans them whenever something weird happens out of habit. ;)

Farrar

[Bitsyncmaster]

A poor ground on the fuel pump would cause the pump to draw less current as shown in the table I posted on fuel pump voltage.

[sean]

. I think he cleans them whenever something weird happens out of habit. ;)

Farrar

or when he is frying his bacon naked...what?

[Farrar]

A poor ground on the fuel pump would cause the pump to draw less current

Would it also cause the circuit to heat?

Farrar

[sean]

Would it also cause the circuit to heat?

Farrar

A poor ground could be a dirty ground and that could lead to resistance which leads to heat doesn't it? Im really asking here b/c I'm mediocre at electronics at best.

[JIMJAM]

Why is the fuse melting and not working like most do? I do not know how many times it happened to the po but we can say at least twice in 30 years.
Well I have the pump exposed and the car all opened up.
I am first going to replace the fuse/holder and try and start the car.
I am going to leave everything open and try and and all suggestions posted before I zip it up and go driving.

[Bitsyncmaster]

A poor ground could be a dirty ground and that could lead to resistance which leads to heat doesn't it? Im really asking here b/c I'm mediocre at electronics at best.

It would result in heat at the poor ground. The same goes for a poor connection at the fuse. You get heat where there is high resistance and high current. So the bad connecting will get hot and if there is plastic there you will know it. Of course the bad grounds the only thing you might see is the insulation on the wires getting melted. But with grounds tied to the frame all the heat would go there.

[DMCMW Dave]

The fuse box is cleverly:huh: located right above the battery. There is a small vent tube behind the battery that ventilates this space when the car is moving.

If the car sits a lot, especially on a battery charger, acid fumes from the battery corrode the connections. Corroded connections have high resistance, which makes them get hot when you do run the car. Then things melt.

It's important to periodically clean the fuses and contacts, and more important than normal if you leave the car sitting on a charger much of the time.

[JIMJAM]

Hi Dave! Always know you will give some good advice. You, Sean and Bisty always come to my rescue. I owe you all.

Ok, despite my back injury, I first numbed up and assumed the hunchback,torture electrical panel position.:eek5:
I did a simple wire to wire soder and heat shrinked them. The po did a crap job which gives crap a bad name. One of those nasty twist jobs with globs of soder then wraped in cheap tape.
Car started 1st turn! A big storm is brewing so I had to stop but later I will root around the f pump and try and find the ground.
Knock on wood . . . but the car had been running great and I was lucky this happened in my garage. I plan to start carrying a spare fuse/holder and solder gun just in case.
I can remember making fun of Bill R carrying dam near a second car worth of spares.
I do carry a small jack and tools which btw really makes the car handle alot better imo.
I am guessing I carry near 50 pounds of stuff including the spare.
Now a a fuse,solder gun and msc tape,,,,,,


BTW- I got one of those high dollar non venting batteries. I also keep the battery with one of the terminals disconnected and usually the doors are open all the time.

[Bitsyncmaster]

The ground for the fuel pump routes through the inertia switch and then (I assume) into the center console. So don't waste your time looking around the fuel pump unless the PO did some modification.

[JIMJAM]

Thanks. I popped the inertia in/out and also unplugged it,fine sandpapered the contacts and then blew in out with contact cleaner.
If this only happens once every 15 years I can handle it. Seeing a fuse holder turn into a melted blob does concern me.
Wish there was a local mechanic. My wish list......
Fix pass window. Will not go all the way up without help. Numerous scars on my fingers.
Go ahead and do a all around brake servicing. Look and work ok imo but its time.
Find out where my trans is dripping about 2 drops per night during the summer.
Basic all around inspection.
And finally.... Fix the :banghead::rant: speedo:smokelot:
Replaced 3x. Fail! I have been running with a heads up display and gps.
Ive got a new DMC unit,a 1 piece cable to eliminate the counter. They no longer sale the super duper one from England anymore. I have not heard anything about Johns.
I have basically given up. But when and if a qualified person works on my car I would like it done. But I know if I do it and it fails again and I will go ballistic on it.

[Cory W]

...but if you get the infamous short circuit inside the WUR that would cause the fuse to overheat. I don't know why the fuse does not blow when that happens. Hence my recommended fusing of the WUR.

Slight derail, but I think it would be of great benefit to the community if you could possibly please repost your how-to on doing this. It specifically showed which wires to check (they were both yellow?) and how to identify the right one with a multimeter. I had it bookmarked on .com, but never printed it out. Would like to do that on my car finally.

[ramblinmike]

Slight derail, but I think it would be of great benefit to the community if you could possibly please repost your how-to on doing this. It specifically showed which wires to check (they were both yellow?) and how to identify the right one with a multimeter. I had it bookmarked on .com, but never printed it out. Would like to do that on my car finally.

+1

[Farrar]

It would result in heat at the poor ground.

That knocks my theory off the list, then; it must be something else. Thanks!

Farrar

[Bitsyncmaster]

Slight derail, but I think it would be of great benefit to the community if you could possibly please repost your how-to on doing this. It specifically showed which wires to check (they were both yellow?) and how to identify the right one with a multimeter. I had it bookmarked on .com, but never printed it out. Would like to do that on my car finally.

http://dmctalk.org/showthread.php?940-Fusing-your-WUR-(CPR)

[Cory W]

http://dmctalk.org/showthread.php?940-Fusing-your-WUR-(CPR)

I found it overnight after somebody posted in the thread. I had looked under the how-tos, but not resources. I only missed it by what, two weeks? :smashfreak:

[David T]

My theory/guess on why #7 melts is that it is a continuously used circuit so it never gets any chance to cool. Any bad connections cause lower voltage and higher amps which means heat. Finally, a dying fuel pump seems to draw too much current. Add all of these factors together and that circuit gets overloaded. A circuit should never be fused to more than 80% of the intended current draw. It should also have been derated because of the heat in the fusebox area. Obviously Lucas didn't do it that way! As for the battery I put a small hose on it's vent and stuck it into the vent hose in the wheel well. I also leave the cover off the fuses to help dissipate some heat.
David Teitelbaum

[JIMJAM]

Back to square one.
Yesterday replaced the fuse hold and 20 fuse. Car started right up 1st turn. Yaaa
Had to stop for a bad storm. I just went out and tried started. Noticed the missing f pump whirrrrrr. Yup, Will not start.
Fuse looks good,replaced it anyways. Checked v at pump. Nothing!
Back at the rpm relay 12+. Across the fuse terminals-Nothing Jumped rhe relay,nothing
Did a all over jiggle test but it seems overnight I lost my voltage to the pump.
I did fool around with the ineria switch but dble checked it. Unless its possible to pop in that brown relay or what ever it is backwards, I am stumped.
My battery is showing 12.8 but I just put it on the charger to top it off. And I recheched my solder job.

[Ron]

I'd check for/run 12V to the pump to make sure it didn't die.

You do know that whacking the hell out of it when others mentioned the "G" word might have triggered the inertia switch don't you?:deviltail:

[JIMJAM]

Ok, I took the fuse out and replaced it. I ran a jumper to eliminate it. But waste of time as I have no power on it "the brown wire'.
I see it goes into the bundle of joy but where the :swear1: does it come from and where does it go? Isnt that a Ted Nugent lyric. Nah that poontang.
Warning- I am back on some new meds that reduce my already lacking IQ so I am not very much over room temp.
But bottom line. I am a electrical eunuck :eek7: and just need power to the pump. I am notorious for knocking off wires while in that rats nest of British copper crap, I mean quality Lucas electrical heaven, but cant imagine what it is.
What,where, how and huh? :umm: HELP.... Lets start calling them "The 4 HS of Delorean"

Tamir you should not have given me so many emicons to play with. Also, how do I add my infamous, "Owning a Delorean is like frying bacon naked." Under my JIMJAM

[JIMJAM]

3484

This is the brown wire from a smaller bundle that a fuse was spliced into. It was melted and I assumed it was the fuel pump. Replaced it,car started, later nothing. No power across the fuse. I dunno wth it is or what it does. Maybe I am barking uo the wrong tree.

[Bitsyncmaster]

3484

This is the brown wire from a smaller bundle that a fuse was spliced into. It was melted and I assumed it was the fuel pump. Replaced it,car started, later nothing. No power across the fuse. I dunno wth it is or what it does. Maybe I am barking uo the wrong tree.

You may have fixed the wrong fuse. Only way to be sure is to use an ohmmeter or follow the wires.

Fuel pump fuse #7 load side is a small gauge brown wire going to the lambda relay socket. Then that same pin has another small gauge brown wire going to the RPM relay.

So with your meter, find the one that connects to the brown wire on the RPM relay.

[JIMJAM]

Here da deal....
Snooped and saw that the brown wire from the lamda was the one that 20 amp fuse that melted down was tapped off of. So I unplugged the lamda and put it back in. Ign on and I heard the f pump come alive. Then I saw light blue smoke coming off the rpm replay. Its a black one modded by Bitsy. Or was it the lam da??? I dunno.. It was to hot to handle and probably baked inside. Replaced it with a green stock and the car fired right up.
I assume, eityher a bad conn at the lamda or a bad lamda........ I do not know why the rpm relay just cooked. I ran the car for a few minutes and the stock is not getting warm.
I guess I did not fix anything but the car is running. Maybe a new lamda and rpm relay is in order. Then keep my fingers crossed. Jim

[JIMJAM]

Latest- Before zipping the car up I let it idle and tested the v across the pump, 12+
But when I handled the wires as shown they were unconfortably warm to hot. Looks like a unused plug off of this mess but somethings pulling some amps.
Is this normal or should I start running!:eek1:

I got a brand spankin new tester from Sears and need to figure out from the dozens of selections which one reads dc amps. None of my initial attempts showed any reading across the fuel pump terminals.