VanhireBoys

Hi All
For the first time in 23 years my beloved turbo is suffering running issues
What has happened

• The fuel pump started to fail so this was replaced
• After the replacement she didn't run great but I put this down to a low fuel level
• Put about 10 litres in and she went worse coming to a stop on our driveway (lucky)
• Fuel pump ran without issue - DME relay checked and verified
• Reference and RPM sensors replaced as one had got a clip previously - Set up
• Car fired up but was running rough with clouds of black smoke from the exhaust
• Checked AFM for a stuck flap OK
• Checked the air temp sensor resistance and got around 3kohm which is within range
• Checked the ECU engine temp sensor and got around 3kohm again within range
• Pulled the vacuum hose from the fuel pressure regulator at the back - No smell of fuel
• Pulled the vacuum hose from the fuel damper at the front and there was a drop of fuel and it smelled of fuel

What function does this damper perform ? and would it cause rough running and overfuelling ?

I am going to do a fuel pressure test hopefully this eve but is there any point if the fuel damper is faulty ?

Could this be caused by an injector that is stuck open ?

My car is an 87 turbo and is completely standard !

Any help would be greatly appreciated as Id really like to learn a bit if I can !

Oddjob

Disconnect the TPS and see if it will run. Will have a hunting idle, and will drive in limp mode, but it will determine if the TPS is the fault.

TPS might be sending a full throttle signal to the DME. I've had that happen before with similar symptoms as you describe --> running rough with clouds of black smoke from the exhaust

blade7

Depends what you mean by 'limp mode'? Due to an issue with the idle circuit, I've run with the TPS disconnected for a couple of years. And apart from the idle dropping occasionally, it will rev cleanly to 6k +.

Oddjob

The KLR will identify a TPS Fault, obviously with it disconnected. So it runs in the traditional KLR limp mode. No boost and believe the ign timing is also pulled back. No change to the rev limiter. My car the idle didn't occasionally drop, it was hunting and high, fluctuating up and down from 2k+. How the idle screw is adjusted in the throttle body and if the O2 sensor is still functional may impact how the car idles when it doesn't know the throttle is closed.

Also with the TPS unplugged the DME will never go to the full load fuel maps. But if you're running some manual boost control and aftermarket ignition control, may not notice that much. But a stock car won't like an unplugged TPS.

As mentioned above, if the TPS full load switch has failed, the DME will try to run it with full fuel delivery and the engine will stall.

Droops83

A leaking fuel pressure damper diaphragm is definitely an issue and should be rectified. Fuel could be getting sucked directly into the intake manifold, which may be causing your issue, but also might not be all of it.

The damper smooths out the pulsations caused by the opening and closing of the batch-fired fuel injectors. If the damper somehow fails or is eliminated, this wouldn't cause an extremely rich condition as you are experiencing, but it could cause running and tuning issues due to erratic fuel injection quantity caused by the hammering effect in the fuel rail, and/or a cracked fuel rail in an extreme case.

Definitely check fuel pressure---it is possible that either the fuel pressure regulator is stuck closed and causing very high fuel pressure, or there is a slight chance there is a kink or restriction causing the same. I have replaced numerous Bosch fuel pressure regulators on both my own 951 and on customer 911 Carrera 3.2s for this reason. The FPR sticks closed, fuel rail pressure goes sky-high (close to 100 PSI), and the engine either barely runs and belches black smoke or stalls because the fuel injectors cannot open against such high pressure. This is often intermittent.

In either case, the damper and FPR are getting expensive and difficult to find.

Good luck.

walfreyydo

Any fuel related diagnosis begins with a fuel pressure test.

Otherwise you are throwing darts at a dartboard. Measure the fuel pressure so we have some actual data with which to make a diagnosis, instead of wild guesses... Lets go through the diagnosis methodology in the correct order.

Verification of correct fuel pressure will determine next steps (for instance, it will tell us if your FPR/dampener is in good working order). FYI the dampener regulates/smooths out fuel pressure fluctuations when the injectors fire. Having fuel in the vacuum line indicates a torn diaphram in need of replacement-although this may not be the cause of your issue it probably warrants some resolution at some point. I dont believe the dampener is as "critical" of a component of the fuel system unlike the FPR, which is. A fuel pressure gauge should both indicate fuel rail pressure (regulated by the FPR) and fuel pressure micro-fluctuations (regulated by the dampener, while the car is idling), with fuel rail pressure (FPR) being the most important to smooth running of the car.

For reference, review the Clarks Garage engine troubleshooting guide.
https://www.clarks-garage.com/shop-manual/ts-01.htm

blade7

MBC and a Euro variation of Lindsey chips. Probably like a lot of 944 turbos at some point.The car will run up to 18 lbs boost without issues. I had the same problem as the OP years ago, resolved by fitting a new FPR. VEMS in hand, to be fitted when I get around to it.

VanhireBoys

Hi All
Well I got the car sorted out with all your help...! Apologies for not getting back to you all earlier - Life got in the way and the car sat in waiting

• Tested the AFM and TPS and got good results - I was this far in so it was easy to check - Just to rule it in or out !
• Had to rig up my own fuel pressure gauge which took a bit of faffing around
• Ran the pump with a jumper in the fuse box
• Pressure was off the clock and pump was dead headed
• Pulled off FPR return line to the tank and ran again - No fuel back
• Contacted another "Clown friend" (My wife's description not mine) who has a turbo restoration project who gave me a fuel rail with both regulator and damper attached
• Fitted regulator first and ran the pump - All good at 4 bar and pump sounding normal
• Disconnected gauge and put cap nut back on
• Started up no problem and settled into a nice steady idle
• Checked for leaks - No problem
• Out for a test run and you know I got quite a surprise at how much the car had steadily blunted without me actually noticing !! She is really going well now, smooth and torquey

Now the rail will have to be returned to my good friend but I'm having trouble finding the FPR and damper locally so will have to go online - At least now I know what the trouble is and a bonus is the new fuel pump as well - Thanks again lads for all the good pointers - Really appreciated