GeorgeK

Jumping the DME reay caused the pump to run for half a second. No fuse blew.
Powering the fuel pump directly had the engine work.
Never blew a fuse so far.

Indycam

Ok , my bad .
The cutting off of power can't be in the dme relay cause without the dme relay in place the power / fuel pump only ran for 1/2 sec .

So my next test would be ,
run a hot wire with a fuse to the dme relay pin out to the fuel pump .
Will the fuel pump keep on running ?

rattlsnak

That's all it's going to run if you have an alarm or RPM input issue.
This is a problem that can be diagnosed in 30 minutes. There is simply not much to the system. Report back your findings on the pin outs.

GeorgeK

Update: DME relay pinouts checked by my mechanic are correct.

He has ordered a fuel pump, and seems 100% positive that it is the culprit. He also thinks that there is an overload switch in the relay for the fuel pump. I am no longer competent at this level without seeing the car myself, which I do not have enough time for these days.
I'll update as I can.

darth

Dear GeorgeK

If pin8 from the ECU fails to provide ground the relay will open and the pump will shut off. To check, put a voltmeter on pin 8 while the engine starts to crank and if ground disappears the ECU is disabling the pump from running. What size fuse are you using for the pump? It should be 15 amp.



Bill

GeorgeK

Bill,
I will transfer this info to confirm whether he checked it.
At this point he seems set on the fuel pump. I guess I'll have to wait it out.
Thank you.

darth

Dear GeorgeK

Not to sound too cynical, but throwing parts in before fully diagnosing is easy for the mechanic but expensive for you, but then again diagnosing takes time and at the hourly rate some mechanics charge this may be the least expensive way to go, provided it solves the problem.

Bill

GeorgeK

Bill,
as I stated above, I am not paying for this (we have a price agreement for the car on the road and inspected). And at this level of expertise, It is above my head, mostly because I do not have the car at my disposal for measures/checks and work, nor the time now to dwell on it for hours (work, kids, chores...).

I know he knows his way around these cars and I trust he did every check before coming to the conclusion that the pump is the cause of the problem .
BTW the fuel pump fuse is indeed a 15A.

I m however grateful for the input and transfer it to him regularly. So far he had done all the checks mentionned.

rattlsnak

As stated above, there is not an overload switch in the relay. If all the pinouts are good, and you have power being supplied to the pump, but it still wont run, then yes, your pump is bad. If power is not being supplied to the pump, then it's not the pump causing the problem.

Don't make it any harder than that...

Indycam

With a hot wire right to the pump , the pump runs and the engine does also .
Hard to see how a pump can be ok with a hot wire but bad with the normal wires .
Its also hard for me to see how a "mechanic" can blame a part like the dme relay that was out of the circuit, for shutting down the pump .

rattlsnak

exactly my point...

Indycam

Indeed .

GeorgeK

That is the core of the riddle. It runs with a hot wire, does not with the normal setup, yet the relay pinout is OK, and no fuse blows. The only hard fact anomaly we see is that the fuel pump draws too much current when it runs hardwired. All the rest is within normal specs.

If it was clear I would not be asking here.

I don't think he is blaming the DME relay, rather the fuel pump relay.

I would also be grateful if there were no negative remarks towards my "mechanic" as Indy puts it. He's been doing 911s only for 35+ years, and so far has never been stumped like that.

rattlsnak

George, we all know its frusrating and we are all just trying to help, but if there is no power going to the fuel pump without jumping it, then there is another problem. It's as simple as that. When your guy mentions that he thinks there is some kind of over protection circuit, it questions his abilities to us. Of course, we are not there and many good techs have been stumped over lessor issues.
Good luck and let us know what you find..

GeorgeK

There is in fact one burst of electricity to the pump at every start, about half a second. The engine (and fuel pump) runs for less than a second and stops right after that.

This is what is very weird. swapped DME relay, fuel pump relay, Motronic, no dice. DME relay pinout is correct.
Hard wiring the pump lets the engine run, but current draw is very large. With every check correct, but the pump current draw, I am having a hard time countering him when he says the pump is the culprit.

No bad feelings at all, I am curious to the solution. I myself would look into the alarm module, but it seems to be OK.