Car died. Need Help - Fuel Injector Weirdness

[Dean924s]

First off I have also posted this over at Clarks but figured I would ask here as well as this one has me scratching my head.


The car died down the street got it home and verified I have spark (not DME control I have a stand alone EDIS system)

Injected carb cleaner in to the intake car starts and dies.

Jumped Fuel pump. Pump runs runs no start.

Disconnect jumper and I can here the pump run

Check pressure t the rail all is good.

So I thought lets remove an injector lead and put a volt meter on it. I should see voltage if it is firing.

Pull the lead and put meter on it crank the motor and it fires but is running like it is on three cylinders (cause it is) clime out and plug in the injector and it dies immediately.

Try cranking and no start not even a kick it just turned over.

Unplug the #4 injector and it fires rite up.

I am betting I have a bad DME. Something in the injector circuit has gone bad and by removing one injector from the circuit it is allowing it to put enough volts / amps to the others so it runs.

Anyone got any thoughts ideas?

I have never seen / heard of this one before.


Many thanks!!!!

(I guess I may have to move my MS project up a bit if it is DME related)

[Techno Duck]

I bet your injector harness is shorting out if its original. Cut the rubber boot off the connectors at the injector harness and take a look at the wiring underneath. If all the wiring looks ok, trace the harness back to the firewall and cut the wire sheathing back at any area you have tight bends and also inspect the insulation.

This is the wiring at the DME temp sensor on my car but i have fixed a few injector wires on friends cars that looked exactly the same. Mind you the wiring looked perfect (albiet 20+ years old) before i cut the boot back.



This is a very common problem.

[Rasta Monsta]

If you have this issue, TX Blake has a great writeup on rewiring these Bosch connectors over on his website.

[Dean924s]

EDIT see next post
==================
Well I think I figured it out.

I took the DME out and went over it with a magnifying glass and re soldered everything.

I had to add some solder in some places and there were definitely some cold solder joints. I had been over it about 5 years ago but not with this amount of diligence. I only went after what "looked" bad. With a magnifying glass things were much clearer. There were more than a couple suspect solder connections.

Anyway I plugged it in and started rite up. It is also idling much better and seems to rev much quicker.

[Dean924s]

No Joy

It ran for about 4-5 minutes and then reverted back to the same. I have discovered that as long as one injector (any injector) is unplug it runs. Plug it back in it dies. Since there are two separate circuits for the injectors (1&2) and (3&4) and unplugging any injector causes it to run I don't think it is in the harness. I ohmed the injector connectors and there does not appear to be a fault. I checked voltage and it was good. I also ohmed all the injectors and they checked out as well.

So what do you all think? I have not split open the injector plug covers yet. Before I do this I will unplug the DME and ohm out the injector wiring in the harness but I am getting the feeling that it is in the DME not a wiring problem due to me re soldering the DME and it worked for a short period of time.

[Dean924s]

Thinking about this more would it be possible that the FPR or the Fuel pump is on the way out and that it is not generating enough pressure to run four injectors but with only three attached the reduced fuel consumption lets build enough pressure to drive the three?

Ohya I direct wired the pump and there is not difference. I inspected the vacuum line on the FPR and it was dry (no fuel)

Ya I am reaching here. I have been around 944's since the mid 80's and I have never had a car do this.

[Dean924s]

From Clark's

When the fuel pressure runs too high, the fuel injectors draw too much current causing the injector drivers in the DME computer to shut down. Disconnect on fuel injector connector and attempt to crank the engine. If the engine starts, where it would not start with all injector leads connected, the fuel pressure regulator is bad and should be replaced. Disconnecting one fuel injector plug reduces the injector driver current sufficiently to get the injector drivers to fire.

Wish I could say I figured it out but Friends at GRM pointed this out to me.

Now another question. Can I use a 951 FPR in a NA car? I would think you can as it will never see boost. It will just be running in the "NA" part of the FPRs range.

[CatsEyes]

Originally Posted by Techno Duck

I bet your injector harness is shorting out if its original. Cut the rubber boot off the connectors at the injector harness and take a look at the wiring underneath. If all the wiring looks ok, trace the harness back to the firewall and cut the wire sheathing back at any area you have tight bends and also inspect the insulation.

This is the wiring at the DME temp sensor on my car but i have fixed a few injector wires on friends cars that looked exactly the same. Mind you the wiring looked perfect (albiet 20+ years old) before i cut the boot back.



This is a very common problem.

Just bumping an old thread here for other people's information.

Recently I had an incident where the car died at home without fuel with no warning. By trial and error I discovered that jiggling the electrical connector on the fuel injector for no. 2 cylinder could get it started (or make it stop). I was mystified: why all four cylinders? Put it on the to-do list for a free day.

More recently the car died at work, with no fuel or spark, but with tach bounce. The jiggling trick worked for a few seconds, but no longer. Had it towed to a local auto-electrician, and explained the jiggle-thing. But of course had no explanation as to why that would cut off all fuel (as opposed to just one injector), or why no spark.

Because of the no-spark/no-fuel condition the repair dude took the after-market immobiliser out of the system (which was OK by me: I'd wanted it out for a while, because it was a lousy job from two owners back).

It ran OK for a couple of days, then died again at a petrol station. I managed to get it home (a full 50km) with the jiggle-trick.

Then I found this thread, and Techno-Duck's post, and cut the boot off the electrical connector. Lo and behold, it looked almost exactly the same as TDuck's picture, only a little worse. Insulation worn or burnt away. Positive and ground wires all mixed up together in a noodle mess; some torn.

So I'm here to confirm TDuck's earlier advice. If you're losing all fuel randomly, be aware that even one short in the fuel system electricals can be enough to cut off fuel to all cylinders instantaneously.

I'm still not sure about the no-spark thing, except it hasn't recurred. Any thoughts on that? Was it maybe the immobiliser, or something else?

[eddie1414]

Clark's Garage Home Page
Check fuel regulator symptoms iam pretty sure that is the.problem

[Dean924s]

Originally Posted by eddie1414

Clark's Garage Home Page
Check fuel regulator symptoms iam pretty sure that is the.problem

Yep it was. I figuared that out two years back.