Fuel Injector weirdness with my 924s: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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Nov. 27, 2010 6:15 p.m. dean1484 Dork
So car dies today get it towed home.

Narrow it down to fuel.

I was messing with things and discovered that if I unplug any one of the 4 injectors it runs (bad but it runs)

I pulled the DME and went over the whole thing with a soldering iron. The car appeared to work normal for about 5 minutes then died and revered back to no run unless one injector is unplugged.

Since there are two injector circuit (one for cylinders 1&2 and one for cylinders 3&4) and unplugging any of the injectors makes it run I don't think it is a wiring harness issue.

I ohmed the injectors and they checked out (2.4 R). I ohmed the harness and it seemed ok. I checked voltage at the injectors and it was ok. I have yet to unplug the DME and ohm out the harness back the to DME. Tomorrow mornings project.

So My thoughts
1. DME has gone bad
2. Fuel pump has gone bad and can only keep up with three injectors
3. FPR has gone bad or is dying (I checked the vaccule line and there was not fuel)
4. ??????
Anyone got any ideas?
Nov. 27, 2010 6:32 p.m. Type Q HalfDork

Off the top of my head, you might check the impedance on the injectors to see if one of them is significantly higher or lower than the rest. This might mess with ability of the DME to trigger them.

I assume you have done this already, but check/clean the grounds on everything.
Nov. 27, 2010 6:45 p.m. dean1484 Dork

Yup ohmed the injectors all was good.

I have not done a ground check
Nov. 27, 2010 10:27 p.m. EricM Dork

DME relay. I carried a spare in the glove box at all times.
Nov. 27, 2010 10:30 p.m. pigeon Dork

Clark's Garage says fuel pressure regulator is bad: http://www.clarks-garage.com/shop-manual/fuel-16.htm

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.
Nov. 27, 2010 10:31 p.m. Woody SuperDork

EricM wrote:

DME relay. I carried a spare in the glove box at all times.

Me too.
Nov. 28, 2010 7:05 a.m. dean1484 Dork

In reply to EricM:

I carry a jumper that I made up years back.
Nov. 28, 2010 7:09 a.m. dean1484 Dork

In reply to pigeon:

I think you nailed it. I never read that part of Clark's manual. . I think I have a spare FPR in my parts pile. I know I have a FPR from a 951 I wonder if that would work? Since it would only be using the vacuum side of things I think it should. Only one way to test it out. Otherwise I have a rail I made up that I can use a generic unit. I will have to see if the local parts store has any in stock.
Nov. 28, 2010 12:32 p.m. dean1484 Dork

As a follow up I put the 951 regulator in my car and it works perfectly.
Nov. 28, 2010 1:28 p.m. pigeon Dork

I like happy endings! :)