348 Hot Start Issue: I Have Tried Everything!

Hey guys I'm hoping somebody can point me in a Direction that I haven't already tried to solve this hot start issue. I've read hours and hours and hours of archived threads on this topic. The car is a 36,000 mile 1992 348 TS. The car runs and runs well but has the typical hot start problem 90% of the time. It's been this way since I bought the car. Starts perfect when cold or warm but when hot it behaves like the classic voith flywheel grease issue. I recently repacked the flywheel meticulously and replaced the triple seals and it made no difference at all whatsoever. I have also tried the technique with starting it in gear with the clutch depressed this makes no difference either. On a positive note, 100% of the time when it exhibits the hot start problem it will ALWAYS start if I apply Full Throttle to the gas pedal while starting.
The following is a comprehensive list of everything I have tried so far: each and every single one of the following made no difference at all whatsoever. None!
Replaced fuel pressure regulators
Replaced crankshaft position sensors
Replaced camshaft position sensor
Replaced air filter
Replaced spark plugs
Replaced fuel filters
Replaced relays for fuel pumps and injectors
Ran fuel low and refilled with 93 octane
Again, to reiterate, ALL of the above were done and the car was tested numerous times afterwards and NONE of the above made any difference at all whatsoever.
I have a lot of different theories of what it could be and my leading theory is that possibly there might be a leaky injector which is flooding the engine at shut down and then when you go to start it it misbehaves and then applying Full Throttle starts it but I have not delved into testing this Theory because I can't figure out for the life of me how to even get a pressure gauge hooked in line. Those fittings are metric inverted flare fittings.
Any help would be greatly appreciated. I've been on this forum for 20 years now and I must say I've never had to take my car to a shop....EVER! Again very appreciative!

 

Thank you both for the excellent advice and information. I've been wanting to yank the injectors and have them cleaned for a long time just on principal so hopefully I will get to that ASAP. I will absolutely check all those values as suggested and Report back.
The fuel pressure regulators are Standard Motor Products PR 298 drop in replacement but when I replaced them they did NOT help my hot start problem at all! And surprisingly one of them was actually leaking slightly out of the vacuum fitting! Moreover I was never able to obtain a pressure rating on those. I even called standard Motor Products and they had no clue as they have been discontinued.

 

So my original FPRs were Bosch 0280-160-738 with 3.8 bar stamped right on the casing so that is not the problem. Plus when I replaced these with the Standard Motor Product FPRs it made no difference at all whatsoever in the hot start problem. I like to test things thoroughly one at the time and therefore eliminate them and move on to the next...... soooo just to update I decided to check your first suggestion which was to look at the coolant temp sensors and while tearing things apart to get to them, unbelievably my left hand fuel injector harness coupling was loose and when I opened it up most of the pins and sockets were corroded green! I cleaned them up thoroughly put it all back together and have not tested it yet bit I have high hopes that maybe just maybe this might have been the problem. If not I'll move on to your suggestion of checking coolant temp sensors and check resistance values. Also there currently are no codes so I suppose the oxygen sensors are okay but then again they are 33 years old! I'll do a few test drives today and report back the result of cleaning the harness plug for the injectors.

 

Excellent question. So if I restart immediately after shutdown it starts back up fine which would indicate that it is NOT the dreaded clutch grease issue. It definitely is related to the car sitting a while. I'm going to test later today a few times after cleaning the harness then I will try ohming out the coolant temp sensors.
On a side note I finally have ordered some reverse flare fittings to install an inline fuel pressure gauge which I can install and run the engine at the same time so I can test each Bank for pressure and leak down. They won't be here till Wednesday but will report back ASAP.

 

Okay I tested the car after cleaning the corroded fuel injector plugs...no difference at all whatsoever. I ested it numerous times with several spirited drives. Then as recommended I checked the coolant temperature sensors. They both are NOT correct as per the chart. At 85 C both sensors ohmed out exactly 826 ohms which is not correct as per the chart but since they're both the same, it kind of tells me that they're probably okay? I've got the fittings coming Wednesday hopefully to perform the fuel pressure testing but I think you guys are right it's definitely one or more leaking injectors flooding the engine. Will definitely report back ASAP

 

Regarding injectors I do have a question rather than sending these off for cleaning and or rebuild I might just consider replacement and people are all over the board with recommendations. What do you guys recommend for replacement? A popular one that pops up often is a Porsche injector
0280150947. Open for suggestions!

 

I'm going to work on this car every single day until I figure this out cuz it's driving season down here in Florida!
As a matter of fact I just got done pulling the right side fuel injector rail and my plan is tohconnect the fuel fittings back up, put a water bottle under each injector, yank all the plug wires and crank the engine over and look for spray pattern and/or leakage. Will definitely report back! And of course we'll do the left side as well.
As far as the crank sensors I agree they should be within spec for the 80° that they were at but the fact that both of them ohmd out at exactly the same reading makes me suspect how could both be bad? Plus the thing is running so slobbering rich and flooding out I think it's got to be injector related but will definitely positively report back.

 

Outstanding information thank you. Well I must confess I ohmed out the coolant temperature sensors in the car with an 85° C warm engine.
After I perform my injector leak down test with water bottles this morning, which I will report back, I will definitely pull those coolant sensors and test them in a bowl of hot water. I thought it could be done in situ. Regarding the injectors unbelievably if you put the part number in they are available on eBay and Amazon super cheap new or rebuilt so I would just go that route rather than monkeying around having these things cleaned and or rebuilt.
For example, as mentioned on other posts OEM part number 0280150731 is available with that exact part number on Amazon eight of them for 60 bucks! Brand new! They show as fitting a Ford Explorer! Incidentally when I removed the injectors I was shocked to see what appeared to be black mud caked up on the head of each injector it's amazing anything could even come out of it I guess it's just years and years and years of soot and oil and egr exhaust gases built up. But inside each injector and inside the rail was absolutely spotless and clean. The inside of the fuel rail shines like a diamond.
I'll check my vin range to make sure the 3.8 is the correct FPR
Will definitely report back later today again I appreciate all of the interest and suggestions.
I'm going to quote someone that said this like 20 years ago.....Do you mean to tell me it's actually okay to drive these cars!

 

These cars are so aggravating I don't know why we drive them! So like I said I was so hopeful that the corroded wire harness was related to the problem somehow but it was not at all whatsoever. You guys had pretty much convinced me that I had one or more leaking injectors which was flooding the engine after sitting hot and was so excited to test this Theory I just got done pulling both sides of the injector rails putting empty water bottles under each injector and cranking over the engine fully expecting to see leakage and they are 100% let me repeat 100% tight not one single of the eight injectors leaked not one drop! I then hooked up the electrical harnesses to the injectors and had my neighbor look and he reported seeing " a nice spray pattern on each injector" now I'm completely stumped I'm thinking about replacing the injectors with some cheap Chinese knockoffs just for the hell of it but I feel like this is not my problem but for how inexpensive it is why not at least try? I also plan to do fuel pressure rail measurement on both sides as soon as I get all of those fittings. Going to have to soul search for a bit on what to do next. Back is killing me
These are not easy cars to work on

 

Forgot to add.... I checked my engine number and it is in the later series engine number using of the 3.8 bar FPR. We'll report back after I do the fuel rail pressure test