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Won't run unless I pull the fuel pump fuse

Old 10-11-2015, 02:24 PM
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jloby18
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Default Won't run unless I pull the fuel pump fuse

Here's the problem I'm having, I have an 87 944 turbo. It will not run unless I pulled the fuel pump fuse. With the fuel pump fuse in it sounds like I'm only firing on two or three cylinders. I'm getting spark on all 4 plugs new wires new spark plugs new distributor rotor I'm getting fuel to the fuel rail evenly distributed on all four injectors. I was driving home from work when the car lost all power and I was barely able to make it off the road the car was sputtering and I can smell of fuel coming out of the exhaust. With the fuse in I give the car throttle it dies right away I stopped the car pull the fuse and the engine runs smooth I'm able throttle it up as soon as I get off the throttle the car will stall. Has anyone had this issue is it sounded like the fuel pump is bad? Could I be having a DME issue?
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Old 10-11-2015, 03:56 PM
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Tom M'Guinn
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Which fuse exactly are you pulling out?

At any rate, have you checked your fuel pressure?
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Old 10-11-2015, 09:31 PM
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mikey_audiogeek
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Agree with Tom.

Fuel pressure might be too high, which causes high current on the injectors, which causes DME to shut down.

Check fuel pressure. If too high, replace FPR.

Cheers,
Mike
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Old 10-11-2015, 09:34 PM
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jloby18
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I believe it's fuse 43. I was speaking with one of my buddies when he suggested it could possibly be the fuel regulator. I have a 3 bar as I'm running the Lindsey Racing 300 rear wheel horsepower kit. On my MAF I was able to lean it out as much as possible so I could at least get the car running good enough to get it up the hill into my garage. My wideband is pegged on the rich side at 10. I'm going to dig into it a bit more tomorrow see if I can see what pressure I'm getting on the fuel rail.
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Old 10-11-2015, 10:05 PM
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jloby18
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A quick update. I took the 3 bar out replace with the stock pressure regulator. I'm in the same boat still running extremely rich. Could my DME have gone bad? if so I have a normally aspirated DME laying around would that work or is it different from a Turbo?
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Old 10-12-2015, 12:31 AM
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Tom M'Guinn
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The DME's are different.

Did this problem start out of the blue or did it start after you installed parts.

I assume you meant fuse 34? Can't say I've ever tried it, but it's counter-intuitive to think the car would even run at all if you unplugged the fuel pump? Does it run a long time that way?

Lots of things can cause the motor to run too rich -- mismatched parts, bad fuel pressure regulator, bad O2 sensor, bad temp sensor, stuck injectors, bad MAF signal, harness problems, bad DME solder joints, etc., etc. A pronounced problem like this shouldn't be too hard to track down, but you need to go after it methodically Let us know the fuel pressure when you test it.
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Old 10-15-2015, 07:15 PM
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kev951
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one or more fuel injector could be stuck open and or the wiring harness for the injectors could be shorted.. look for raw fuel in the vacuum lines to the damper and fpr for signs of them failing. take 12v to each injector and listen for them to click anytime they are energized (engine off) ...
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Old 09-26-2018, 04:36 AM
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Jacob AbuKhader
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I know this thread is 3 years old but did you ever find the solution? Having the same exact issue, gone through fuel pump, filter, AFM, AOS seals, plugs, coil, battery, starter, vac hoses, jboot, on and on and on. Canít figure it out.
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Old 09-26-2018, 06:33 AM
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The first thing I would look at is your DME engine temp sensor for proper operation. If it goes bad it will run rich because it’s telling the DME it’s cold out. Maybe even check for a smashed return hard line? I had that Issue before. That is if your secondary ignition (coil/cap/rotor/wires/plugs) are working properly and you have fresh fuel.
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Old 09-26-2018, 06:41 AM
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Jacob AbuKhader
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When you say return line, do you mean the return line from the regulator to the fuel tank? What kind of symptoms where you having that keadbyou to check that? Iíll have to look into that some more. Itís such a strange issue. The other day the car only ran on 3 cylinders had to keep my foot on the gas to keep it alive. As soon as I pulled the fuse for the fuel pump, it idled perfectly until it burned the gas in the lines. Ive got my own thread on it started up as well. Still canít seem to find the answer.

Forgot to mention coolant temp sensor is brand new, DME relay is about 1 year old, and one of the first things I replaced was the regulator itself. (Car used to smoke badly and was diluting my oil from running so rich)
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Old 09-26-2018, 07:15 AM
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Well I caught it by accident while chassing an issue with the rear brakes not getting fluid. My 951 was a track car that didn’t always stay on the track apparently. Both, the rear brake line and fuel rerun lines were smashed and the primary fuel line only had a little office for fuel to get thru. All at the same location behind the passenger wheel well. So it actually ran fine. It just did t want to stop.
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Old 09-26-2018, 07:19 AM
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Jacob AbuKhader
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Thatís a helluva discovery!
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Old 09-27-2018, 10:20 AM
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I've read a bad ecu ground can cause running rich problems.
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Old 09-27-2018, 12:25 PM
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Jacob AbuKhader
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Ive gone through and cleaned some of them, others looked okay. I changed my fuel pressure regulator and smoke went away but now itís back on startup, could the damper be the culprit?
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Old 09-27-2018, 09:53 PM
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Yes it could be. If the diaphragm ruptures it will dump fuel into the intake thru the vacuum line. That would be easy to check. Pull off the hose and cap the intake side, then see if it dumps out of the dampeners vacuum hose connection.
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