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I have had a hot start issue with my 3.0 engine for over a year now. The car is a 74 but the engine is an 80 SC 3.0 (hence my name). I posted for some advice when the issue first started (when I first got the car), good advice then - thank you Porsche people. I went through all the known glitches and went to 2 specialty shops. Spark plugs, distributor cap, ignition coil replaced x2, accumulator replaced, check valve replaced. At one point, the car was shutting off when driving in hot weather (scary). One specialty shop was reportedly very thorough, they found the new ignition coil was faulty and replaced again. So am on my second new ignition coil. Car is no longer shutting off on the road. The car was in that shop for well over a month and they told me they checked everything, fuel pressures and fuel pump. In fact, both shops confirmed "not the fuel pump, pressures are fine." Well, the weather got cooler and the car ran nicely after the last coil was replaced, I mainly used it during the weekends for short distances. Now, the summer heat is back and the gremlin is back. If I turn it off at a gas station, seems to be ok in the short term but after getting the car warmed up and then off and sitting for 30-60 minutes, won't start. The car cranks nicely, won't catch. Car has to be completely cooled off before it will start again, maybe another 30-60 minutes of waiting. Almost like a vapor lock. I got in touch with the previous owner who filled me in that he also had this issue a couple times in the hot weather a year or two prior to selling the car, but the car was not used often at all. Other valuable information, since I have had the car, it has had a rich smell of fuel, even when sitting. I get into the garage, cold or warm, there is a pungent smell of gasoline, mainly from the engine. I didn't think much of it at first and other owners have mentioned similar smells from their AC Porsches, but this seems to be more. I did change the float a few months back, the smell is not coming from the tank or front. I also learned that the warm up regular has been replaced a few years back. The original WUR starved the car and instead a WUR from a 928 was put in, maybe 20 years ago, and the car has run fine with it. The CDI box was replaced about a year ago as well, this shorted after the alternator went, this was also "thoroughly checked out, CDI is fine." Could the gremlin be he WUR? Could it be timing? I am limited in my ability to most of this myself and relied on the input of the mechanics but it seems this problem may have evaded them. Am I just dealing with an older car in the hot weather and have to reassess my expectations? Any thoughts?
I have had a hot start issue with my 3.0 engine for over a year now. The car is a 74 but the engine is an 80 SC 3.0 (hence my name). I posted for some advice when the issue first started (when I first got the car), good advice then - thank you Porsche people. I went through all the known glitches and went to 2 specialty shops. Spark plugs, distributor cap, ignition coil replaced x2, accumulator replaced, check valve replaced. At one point, the car was shutting off when driving in hot weather (scary). One specialty shop was reportedly very thorough, they found the new ignition coil was faulty and replaced again. So am on my second new ignition coil. Car is no longer shutting off on the road. The car was in that shop for well over a month and they told me they checked everything, fuel pressures and fuel pump. In fact, both shops confirmed "not the fuel pump, pressures are fine." Well, the weather got cooler and the car ran nicely after the last coil was replaced, I mainly used it during the weekends for short distances. Now, the summer heat is back and the gremlin is back. If I turn it off at a gas station, seems to be ok in the short term but after getting the car warmed up and then off and sitting for 30-60 minutes, won't start. The car cranks nicely, won't catch. Car has to be completely cooled off before it will start again, maybe another 30-60 minutes of waiting. Almost like a vapor lock. I got in touch with the previous owner who filled me in that he also had this issue a couple times in the hot weather a year or two prior to selling the car, but the car was not used often at all. Other valuable information, since I have had the car, it has had a rich smell of fuel, even when sitting. I get into the garage, cold or warm, there is a pungent smell of gasoline, mainly from the engine. I didn't think much of it at first and other owners have mentioned similar smells from their AC Porsches, but this seems to be more. I did change the float a few months back, the smell is not coming from the tank or front. I also learned that the warm up regular has been replaced a few years back. The original WUR starved the car and instead a WUR from a 928 was put in, maybe 20 years ago, and the car has run fine with it. The CDI box was replaced about a year ago as well, this shorted after the alternator went, this was also "thoroughly checked out, CDI is fine." Could the gremlin be he WUR? Could it be timing? I am limited in my ability to most of this myself and relied on the input of the mechanics but it seems this problem may have evaded them. Am I just dealing with an older car in the hot weather and have to reassess my expectations? Any thoughts?
Since the problems are resurfacing with the warmer temps, I would bring it back to the two specialty shops, start with one where the car was for an entire month, and have them diagnose and fix this properly instead of swapping parts without root causing the issue. Are these well known Porsche specialist outfits familiar with the 80 3.0 setup ? The CIS system you have is a transplant with mismatched components so troubleshooting on the Interwebs gonna be a challenge. If you are game however, start by posting some pics of the engine and whatever the shops reported on their work orders.
It's either a fuel or ignition problem, i.e. it's as simple as that to begin with, right? To eliminate fuel as the problem, get some carb cleaner and spray it into the intake.
If it starts, guess what the problem is? Then focus on the fuel components. It's so simple when you use logic!
I have had a hot start issue with my 3.0 engine for over a year now. The car is a 74 but the engine is an 80 SC 3.0 (hence my name). I posted for some advice when the issue first started (when I first got the car), good advice then - thank you Porsche people. I went through all the known glitches and went to 2 specialty shops. Spark plugs, distributor cap, ignition coil replaced x2, accumulator replaced, check valve replaced. At one point, the car was shutting off when driving in hot weather (scary). One specialty shop was reportedly very thorough, they found the new ignition coil was faulty and replaced again. So am on my second new ignition coil. Car is no longer shutting off on the road. The car was in that shop for well over a month and they told me they checked everything, fuel pressures and fuel pump. In fact, both shops confirmed "not the fuel pump, pressures are fine." Well, the weather got cooler and the car ran nicely after the last coil was replaced, I mainly used it during the weekends for short distances. Now, the summer heat is back and the gremlin is back. If I turn it off at a gas station, seems to be ok in the short term but after getting the car warmed up and then off and sitting for 30-60 minutes, won't start. The car cranks nicely, won't catch. Car has to be completely cooled off before it will start again, maybe another 30-60 minutes of waiting. Almost like a vapor lock. I got in touch with the previous owner who filled me in that he also had this issue a couple times in the hot weather a year or two prior to selling the car, but the car was not used often at all. Other valuable information, since I have had the car, it has had a rich smell of fuel, even when sitting. I get into the garage, cold or warm, there is a pungent smell of gasoline, mainly from the engine. I didn't think much of it at first and other owners have mentioned simil smells from their AC Porsches, but this seems to be more. I did change the float a few months back, the smell is not coming from the tank or front. I also learned that the warm up regular has been replaced a few years back. The original WUR starved the car and instead a WUR from a 928 was put in, maybe 20 years ago, and the car has run fine with it. The CDI box was replaced about a year ago as well, this shorted after the alternator went, this was also "thoroughly checked out, CDI is fine." Could the gremlin be he WUR? Could it be timing? I am limited in my ability to most of this myself and relied on the input of the mechanics but it seems this problem may have evaded them. Am I just dealing with an older car in the hot weather and have to reassess my expectations? Any thoughts?
i think before any parts are tried he needs to get pressure gauges on and see if it is holding residual fuel pressure when engine is hot.
of course the shop will say its fine if it isnt doing it when they are testing it . the hot times it happens get the gauges on gain fuel pressure then watch it and see if it holds.
also how hot is hot? hot in Canada might be 85F out, hot in Texas night be 120F out.
when it is exhibiting the issue and wont start if the main spark plug lead is pulled off the top of the distributor cap and is held close to a ground and the starter is tried is there spark ?
I just think no one is asking the right questions.
Thanks all for the input. Hot is Southeastern US hot, 80s-90s F hot, upwards to 100s.
Anyway, after getting stuck with the problem again (in a hot parking lot), I went ahead changed the things that I could. I do not have the skill set or tools to check fuel pressures. I do/did have an extra WUR and put that in. Turns out the one that was in there was shorted, the resistance was all over the place, 70s-140s and not staying still, the one I put in was good with steady resistance. Almost immediately, the smell of fuel cleared my garage. Also, the timing was a bit advanced so I retarded a bit, took away some of the power/performance but starts much better when cold and warm. I am hoping this was the problem after the previous owner had also swapped the WUR and warned me about this. I suspect this was a major culprit. Perhaps the car was running too rich, too much fuel was flooding it out and with timing too advanced, wouldn't catch... not sure if I am right but a thought I went with. So far, so good. Even though the past few days have been cooler, got the car hot, left her outside in the sun for an hour after driving and she started right up after 2-3 cranks. Hopefully that settles it but if not, I see myself making a trip to buy fuel pressure gauges and an evening reading more forums and watching YouTube on how to check fuel pressures.
Checking FP in the CIS world means measuring the FP at the WUR, namely the cold control and warm control pressure and comparing those with OEM chart specifications. You're already there with the WUR fuel lines disconnected and all you need is a good set of CIS/Kjetronic compatible gauges hooked up inline to that.
You mentioned you installed a spare WUR. Each version has its own pressure characteristics, and they are not necessarily interchangeable. Here are the specs and graphs for 1978, 1979, and 1980 SCs. We can get you the correct graph based on the part number stamped on the side. You need the fuel pressure gauges to test. Don't get the Harbor Freight set, they are probably more trouble than they are worth.
The other factor is how the 1980 engine was installed in your 1974. A 1980 has lambda control, so there are electronics connected to the O2 sensor. You will probably have to figure out if this system is working. I think the computer is supposed to be under the drivers seat, but I would start by seeing if you have an O2 sensor and if it is connected.
Thanks for the graphs, and the website, and all the recommendations. I am planning on getting gauges and learning how to test. Luckily replacing the WUR was pretty easy so sounds like this next step should be pretty straight forward.
In terms of the install, I have limited information but from my understanding, no computer. In fact, the previous owner mentioned he had gotten rid of the computer many years ago. The originally WUR that came with the 80 engine was also removed/replaced when the engine was installed (late 1990s). Apparently, the car underperformed and swapping out the original SC WUR with a 928 WUR solved that issue... until I got the car.
05-29-2021, 10:47 AM
Hot start in 3.0
