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Wow, I just read the whole thread. There's alot going on here! Hate it for you! Unfortunately, I don't come with volumes of 944 knowledge, but I've fixed a thing or two in my time. My son and I recently joined the 944 world and ran into similar wiring woes that had to be figured out. Turns out our (his) 86 NA had a wire harness swap from a turbo. There are differences.
The first thing that hit me over and over was the obvious fuel pump / fuse operation. I feel like your putting too much faith in fuse in or out meaning anything (given it could have been hacked over time). There's no way the car could run that long without a fuel pump running at some point. You've got a fuel pressure gauge now, but it's not clear that you've made use of it, yet. We had fuel pressure issues, as well. That's what you've got to start watching, imo. That and a test light or volt meter reading from the fuel pump directly.
Wow, I just read the whole thread. There's alot going on here! Hate it for you! Unfortunately, I don't come with volumes of 944 knowledge, but I've fixed a thing or two in my time. My son and I recently joined the 944 world and ran into similar wiring woes that had to be figured out. Turns out our (his) 86 NA had a wire harness swap from a turbo. There are differences.
The first thing that hit me over and over was the obvious fuel pump / fuse operation. I feel like your putting too much faith in fuse in or out meaning anything (given it could have been hacked over time). There's no way the car could run that long without a fuel pump running at some point. You've got a fuel pressure gauge now, but it's not clear that you've made use of it, yet. We had fuel pressure issues, as well. That's what you've got to start watching, imo. That and a test light or volt meter reading from the fuel pump directly.
Thanks for the reply!
Ive been focusing on the fuse in/out because that’s the only really consistent symptom I’m seeing when the car dies or refuses to start. I tend to agree with you that there’s no way the car can run without the fuel pump working at some point. Here’s my latest theory...
Ive been focusing on the fuse but ignoring the fact that the relay is what actually provides power to the pump. The fuse only connects the circuit. I have physically put my hand on the pump while the car runs without it and can confirm it doesn’t pump. However, I don’t believe it is “dead” so to speak all the time. Because if I pull the fuse and the relay during a no start, the car will not fire. But with the relay in and the fuse out it will fire.
What I think is happening is during the no start condition is the wires must be grounding, or building massive amounts of resistance and in a way acting like a huge capacitor. So with the fuse out and the circuit broken, the relay stays in the closed position, keeping the circuit with the ignition closed even without the fuse. With 𝖯𝗋𝖾𝗌𝗌𝗎𝗋e in the lines and capatance in the wires, I think the DME might still see the signal from the relay as that the engine must be getting regular flow so the car starts. Until the charge in the wires is used and the pressure in the lines is drained. The reason I say this is because after completely draining the pressure in the lines even with the fuse out the car will refuse to start.
The moment I plug the fuse back in the wires build up charge and the pump runs pressurizing the lines. I think over pressurization is shutting down the injectors or soaking the plugs. Since replacing the FPR the car no longer floods. But does start very very rich. In removing the fuse panels and relay board the wires leading to the loom aren’t burned or broken.
I have no idea if any of that is actually the culprit until I bust out a multimeter and start chasing resistance readings.
Update on the FP gauge: it’s still in production unfortunately it’s not installed yet. I’m hoping soon it will be so that I can see 𝖯𝗋𝖾𝗌𝗌𝗎𝗋𝖾 readings and that will be another big clue. The 924S gauges are in and look great!
I hope the jargin about all the wiring makes any sort of sense. If I’m mistaken in my thinking let me know! I’d hate to start ripping out my seats and carpeting for nothing lol.
Without a doubt these cars can be a PITA. But it’s all part of owning them. Its still a Porsche and it deserves to be treated like one 😁.
Got to assume so given some of your testing. I would check for continuity in the wire from the DME relay base to the fuel pump. If you get some 1/4" male spade terminals, you can push one onto the DME base to test.
Testing the wire to the pump is going to take a long piece of wire to "extend" one of the DVM leads back to the pump. If there is continuity, you know that IS the wire going to the fuel pump which seems questionable at this point. Then check the resistance in that wire. That might help narrow down a wire issue.
Got to assume so given some of your testing. I would check for continuity in the wire from the DME relay base to the fuel pump. If you get some 1/4" male spade terminals, you can push one onto the DME base to test.
Testing the wire to the pump is going to take a long piece of wire to "extend" one of the DVM leads back to the pump. If there is continuity, you know that IS the wire going to the fuel pump which seems questionable at this point. Then check the resistance in that wire. That might help narrow down a wire issue.
Awesome wilco I’ll give that a shot. What sort of resistance readings should I be expecting to see? So I know what’s way out of spec or normal.
It's difficult to give you an "in spec" number for the circuit as the number of connections, actual length of run, and your meter will be factors.
For reference:
- 50' of stranded 16g wire will have about .25 - .3 ohm resistance
- a nice new Amp brand quick connect has about .12 ohms resistance
That said, I'd be looking for .25 - .5 ohm ballpark.
Just connecting the meter and checking across the leads will read some low level of resistance depending on the device. I'd suggest to check the meter alone, then check the 15' of extension wire you're using to get to the fuel pump so you'll know what you're starting with. I'd strip an inch or so of the extension wire, then wrap it neat and tight around one of the meter leads (if you dont have clips) then wrap it with electrical tape to keep it tight and not sliding off.
I think we found the DME relay pinout on Clark's. Memory serves that the wire going to the fuel pump was about 16g, so I'd target that size for testing.
Ultimately, if there was anything sketchy, I'd be open minded to running the fuel pump off a temporary pair of wires taped to the side of the car or whatever to see what happens. You can use the male and female spades to make like 3" extensions to lift the dme relay off its base and also provide a place for you to tap into for electrical testing- that's what we did.
Awesome info. Next time I get a chance I’ll give this a shot and see what happens. As luck would have it I just bought some alligator clips so looks like they will be coming in handy.
Decided ro to start measuring ohms across each fuse in the upper block. I know they are getting volts but I wanted to see what sort of resistance readings I’d get for all of them to get a sort of baseline idea of what should be happening.
With the fuses in and the car running, I got tone and all zeros for every single fuse. Including fuel pump fuse. With fuel pump fuse removed, car running, and meter set to ohms measuring the tabs, I got OL. Which is expected because there was no fuse in.
I discovered why my fuel pump was running without the keys in the ignition. In trying to plug the fuse in I was grounding the fuse for the fuel pump to the fuse no. 1 to the left. idiot.
It did confirm something though. The pump is definitely not running when the fuse is connected. Because with the fuse disconnected so the car could start, as soon as I put power to the fuel pump the car refused to start.
I did this while the car was running without the fuse in place as well. As soon as the pump came on, the car lost all rpm and died. If I took power out before the stall, the rpm would shoot back up to idle and continue to run.
worth noting With fuse in I get 12V to the pump. Whether the car runs or not.
For whatever reason when the pump is added to the mix, the car is not happy. At all.
Decided ro to start measuring ohms across each fuse in the upper block. I know they are getting volts but I wanted to see what sort of resistance readings I’d get for all of them to get a sort of baseline idea of what should be happening.
With the fuses in and the car running, I got tone and all zeros for every single fuse. Including fuel pump fuse. With fuel pump fuse removed, car running, and meter set to ohms measuring the tabs, I got OL. Which is expected because there was no fuse in.
I discovered why my fuel pump was running without the keys in the ignition. In trying to plug the fuse in I was grounding the fuse for the fuel pump to the fuse no. 1 to the left. idiot.
It did confirm something though. The pump is definitely not running when the fuse is connected. Because with the fuse disconnected so the car could start, as soon as I put power to the fuel pump the car refused to start.
I did this while the car was running without the fuse in place as well. As soon as the pump came on, the car lost all rpm and died. If I took power out before the stall, the rpm would shoot back up to idle and continue to run.
worth noting With fuse in I get 12V to the pump. Whether the car runs or not.
For whatever reason when the pump is added to the mix, the car is not happy. At all.
Also worth noting that no damage was done by the accidental groundings. Remember this issue has been happening since January.
it seems the opposite of what I assumed was happening is happening. The pump actually IS getting power WHEN it’s supposed to and is functioning normally. However only when the pump is disconnected will the car start/run until the pressure is bled. Once the pressure is bled the car won’t start with the fuse out. I have to put it back in to “prime” the system so to speak so that the car will start again once it’s out. It’s the only way I can keep my battery alive.
FPR is new... could The damper still be causing his nightmare?
I'm not sure what kind of neg effects a bad damper could have, but I feel like it would be more of a smooth running acceleration issue than what you're experiencing. But I have zero actual knowledge of it to say that for sure, just my assumptions on how its working.
New FPR... Given my recent challenges trying to get a new one, I wonder what new means in your case. New Bosch or new to you or ??? I ended up having to drop some extra coin for an adjustable as the Bosch are no longer available. The adjustables are apparently even quite rare as Lindsey doesn't even have them in stock either.
Also, checking resistance- I wouldn't do it with the car running or with a device connected (if you're checking wires or across connectors or the fuse block). Resistance on coils (solenoids) and motors would be done via the + and - of it, disconnected from the rest of the circuit.
I'm not sure what kind of neg effects a bad damper could have, but I feel like it would be more of a smooth running acceleration issue than what you're experiencing. But I have zero actual knowledge of it to say that for sure, just my assumptions on how its working.
New FPR... Given my recent challenges trying to get a new one, I wonder what new means in your case. New Bosch or new to you or ??? I ended up having to drop some extra coin for an adjustable as the Bosch are no longer available. The adjustables are apparently even quite rare as Lindsey doesn't even have them in stock either.
The dealer supposedly did a 𝖯𝗋𝖾𝗌𝗌𝗎𝗋𝖾 test when they had it, and said it was fine, however no one could give me a difinitive answer so until I put a gauge in I’m going to assume there hasn’t been a test done. My gauge is still in production
Noted about measuring resistances. I’ll measure again with the car off.
The FPR I bought is a brand new aftermarket part I was able to get from my local auto parts store. The brand is GP Sorensen. It was listed as a direct fit for my my car. I think I paid about $70 for it. No complaints from me so far as my oil is no longer being diluted with fuel and my exhaust no longer smokes. Still smells a little rich and the plugs are fouling left and right but I think that’s due to whatever is causing this issue and not the regulator. The rest of the parts i have bought are all also brand new save for the airflow meter that I got from 20th street. However they test all of their parts and I also have a warranty for it. The cap covering the CO screw is still on there so it hasn’t been messed with.
I really wanted the whole rail kit from Lindsey but $500 was a little steep for me, for a car that doesn’t really need it. Interesting that the regulators from them are rare as well.
Hey everybody. I thought I’d take a break from the super depressing aspect of this thread and give everyone a peak at how the new gauges turned out. Installed a set of 924S gauges to match the fuel pressure gauge that’s on the way. Kind of cool that these came with a shift light from the factory.
went with blue LEDs to match the night lighting of the gauge as well as make the needles pop and easy to read. Saw it on a late 944 and really dug it.
also swapped tach to center, (no cutting required, and yes the speedo works without being rotated) a lot of people really hate that but hey, the 924 Carrera GT had a center tach. If the 986, 911, 962, 917, 987, and 914 all had center tachs I think there’s worse things to do to the dash for fun lol.
09-16-2018, 05:06 PM
