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I just read through this entire thread and while I'm still pretty novice on troubleshooting these cars I have a couple thoughts. I had what sounds like a similar problem on my 944 Turbo recently. It ran extremely rough and smokey, definitely misfiring, after running fine a few weeks before.
I thought it was related to fuel pressure as well so I rigged up a fuel pressure gauge for $20 from stuff at Home Depot. I'm not recommending this technique so don't sue me if you burn your car down, but it might work for others too. I had some pretty soft rubber 3/8" gas hose. I got a cheap pressure gauge and used a 3/8" barb to connect it to the rubber hose with a hose clamp. I took the cap off the end of the fuel rail, shoved the hose over the threads and put a hose clamp on it tightly. The soft hose material and tight clamp was enough to seal it over the threads and it didn't leak while I had it installed. Pretty sketchy - I wouldn't run the engine like that without standing right over it watching for leaks - but it helped me rule out fuel pressure as the problem.
In the end I discovered that the connector for either my speed or reference sensor was disintegrating and the sensor had come unplugged. I didn't think the car would run at all without these sensors so I didn't check them right away. Once plugged back in the problem went away and the car runs fine now. Not sure if that matches your issue(s) exactly but I would suspect a bad connection to these sensors somewhere in the wiring. If it is an intermittent fault that could be part of your issue.
The FSM has troubleshooting steps for finding electrical issues in the 944 Turbo volume, with instructions on testing sensors at the DME connector. If they don't appear elsewhere in the manuals its probably similar for NA's so I would suggest following those to rule out some of the electrical sensors. You will need a cheap oscilloscope but that's worth having anyway. Good luck!
Very interesting. I wouldn’t have thought they could run at all without them either. The car does exhibit different cranking characteristics
when I’ve cranked it with the sensors disconnected, however I had no idea bad connections could cause rich running....
If my fuel pressure ends up being normal, I will def. look into this direction as those connectors are in poor state. The new one I was going to install ended up having a male plug while the plugs on the harness are male. It must be for a later car, or just the wrong part altogether.
suddenly 3/4 speakers inside the car don’t work, and every time I try to plug in that wire for the radiator cooling fans I get a huge spark and it blows a fuse. Have not done ANYthing to the wires so this is beyond me. Also noticed that a wire going to the fuel pump fuse terminal is melted a little bit near the connection. I’d like to reconnect everything on this panel with insulated female connections one at a time, I don’t like the bare connectors that close to touching eachother. Another weird thing, in wiggling around that fuse panel somehow I managed to turn the ignition on without keys in the switch. Dash lit up as if the key was turned to pos 2, and a relay clicked. Not sure if our cars run the pump for a second or two to prime the engine for starting but the pump didn’t buzz or hum.
The irony in all of this being the car occasionaly still starts up and runs and drives normally.
I have a haynes manual and I need to check Clark’s but does anyone have a wiring diagram for the upper fuse panel only? I want to have a reference Incase I decide to completely disconnect everything at once to rebuild it.
I’m gonna be so irritated if I have to pull the radio. Think it’s safe to 100% confirm that this is an electrical issue and not one dealing with injectors or mechanical components of the fuel system. In fact I expect to see completely normal fuel pressure once that gauge comes in.
Two big updates! I paid closer attention to the wire that’s melted, it’s not the fuel pump it’s the antenna. The reason my radio, and speakers weren’t working was because what was supposed to be plugged into the lighter, was unplugged and the 12v+ for the clock shorted it and blew the fuse. So all week I have been undoing a POs wire tampering.
My ciggerette lighter now works, my radio/ speakers are all back to working order, and I cleaned a few more grounds to no avail unfortunately.
The best news is that the fuel pressure gauge is in! FINALLY. Got the lighting all tested and working so now I just need to tap into the fuel system somewhere to install the sensor. Pics included. Kind of bummed to find out my clock worked and was just connected wrong the last 2 years but hey, at least it’s space is being put to good use. Peace of mind as well knowing my wires will be insulated and connected safely, properly, and in an organized manner. (Everything’s a mess right now but it’ll be neat and tidy)
once the gauge is fully up and running, I will be sure to come back with pressure numbers.
Tried to match the factory gauges as much as possible. I knew before hand that the colors wouldn’t be 100% matching but it’s closer than it would have been with black and yellow 😁. Love the way it turned out. Exactly what I wanted, without making my car look like a civic.
Im getting 39 psi at the rail which is 10 psi too high.
Testing proceedures ( can’t do it during no start because The car only runs without the fuse in and quickly decreases pressure can’t get accurate reading)
1. Safely prepared to jumper the fuel pump.
2. Ignition on gauge powered no pressure in lines 0 psi.
3. Jumpered fuel pump with key in POS 2 on not cranking
4. Measured pressure until needle stopped. Held for 3 seconds after needle reached peak pressure
conducted 3 times. Same PSI each time.
Running this by everyone to make sure this is a viable test and the results are accurate.
Just to clarify, the car is not running while you’re doing the test? In that case it is within spec (36psi +/-3psi). But one thing that seems odd is that it should hold pressure after you turn off the pump. Clark’s Garage says it should still be at least 14psi after 20 minutes. If you’re starting at 0psi again after each test then your check valve might be bad.
Okay thanks for the corrections. I checked clarks and realized my mistake. I had read 29psi from another forum but I didn’t realize that was the spec for the car running vs off.
Could a fuel pump check valve cause my random dying and starting? If not it might be bleeding pressure from where I installed the sensor.
In any case, if the fuel pressure is fine I’m assuming I must have spark issues then. That’s the only thing I can think of that explains the random stalling while the car is driving, the starting and running without the pump on, I did ground each plug and got spark, but it must be weak, or be drowned out somehow. And then killing the pump allows the plugs to burn off the gas in the cylinders?
If fuel PSI is in spec and the pump works the way it’s supposed to then I have a feeling the fuel system isn’t the issue and neither is the wiring for it, and if the car is still over fueling so bad, it’s gotta be spark. Am I missing something?
Thanks for the input guys. Getting closer to solving this.
Could a fuel pump check valve cause my random dying and starting? If not it might be bleeding pressure from where I installed the sensor.
In any case, if the fuel pressure is fine I’m assuming I must have spark issues then. That’s the only thing I can think of that explains the random stalling while the car is driving, the starting and running without the pump on, I did ground each plug and got spark, but it must be weak, or be drowned out somehow. And then killing the pump allows the plugs to burn off the gas in the cylinders?
I’m not sure what a bad check valve would cause. But I will add that when I was troubleshooting my fuel system it seemed to hold pressure for hours.
I do think you can rule out your spark issue. I think that’s the beauty of a distributor ignition; it’s a pretty simple system. If you checked spark on each cylinder and it looks strong then I don’t think it is the problem.
I’m still leaning towards a sensor problem. In my case it was one of the speed/reference sensors which cause the engine to run super rich. The coolant temperature sensor is a common culprit as well. Or DME issues. I think you need to focus your efforts on finding a problem with one of the sensors and/or wiring. Also forgive me if you have already mentioned this but are your injectors confirmed to be working well? That could cause issues as well.
The injectors are working yes, but I don’t know if perhaps they are sticking open I’m not sure. When the car runs normally unplugging an injector gives me a consistent misfire on the cylinder I cut the fuel from. When the car runs rough or develops a misfire when it’s having one of its “fits” unplugging injector actually makes the engine run even weaker and usually will stall it. This is the case for all 4 of the injectors.
It’s been about 20 minutes and it’s only come down about 6.5psi from 37 to 31.5. (The sensor for the fp gauge was still a little loose causing immediate drop)
Affer about an hour fuel pressure at the rail was still about 7psi. So I’m confident in saying it passes the fuel pressure tests. With the fuse in during a no start the pressure builds back up to the mid to high 30s and holds.
If i pull the fuse to start the car it cranks until the pressure drops to zero indicated and then fires and runs. Revving has no affect. Jumpering the pump and cranking with the fuse in have the same result so this confirms a few things to me.
The pump works
the lines are clear
fuel pressure is good
the check valve is indeed good (I should hope so it’s brand new)
the damper is good
the new regulator isn’t deffective
wiring the pump directly to the battery will result in no change in starting condition
the wiring from the pump to the fuse and relay is not damaged and is not the issue.
I’m definitely not ruling out those speed/ ref sensors, but before I jump to those I’m curious as to what you guys think it might be now that we’ve seen that the fuel pressure is okay.
09-21-2018, 01:31 PM
