My car would always start when cold but if it didn't catch right away, it was often hard to re-start. I never got around to sorting out the IP solenoid so today we fixed it. Sarts every time now - so this part needs to work.
There are several elements that affect starting, both hot and cold, which have been discussed at lenght on these forums. Most starting problems are generally a lack of fuel if the engine otherwise runs normally.
I found a very interesting problem on a customers car recently and the diagnosis may be of help to others. We rebuilt the fuel pump because it was leaking badly and it seemed to be working fine. The engine started well and always started when it was warmed up so there was no reason for me to suspect any problems. I had replaced all of the fuel hoses and the tank was replaced recently so it appeared that it would be trouble free after it left.
The day the car was picked up I went with the customer for a short test drive and the car starte and ran well as usual. When he started the engine to leave it wouldn't fire. This was during the week of unusually hot weather we had during mid March and this was the first time the engine hot soaked in anything but fairly cold temps.
It finally started but it took a lot of coaxing. I would of fixed this had I the chance but he had to leave so I could only wonder if it would do it again. It did.
The car came back over the past weekend to fix a broken hatch cover release cable and to see if we could figure out why it wouldn't start when hot. While the cable was being worked on I started with fuel volume tests.
No fuel volume at the return line. I removed the line going to the cold start and I had a little ressure. Pugged fuel filter I wondered?
Changed the filter which was clean and still little volume at the cold start. I removed the line going to the filter and tested volume right off the fuel pump - lots there. I wondered if there was something wrong with the fuel dampner. I removed the line on the IP where the fuel pressure regulator is and there was just a few drops coming out. By this time we had a pressure gauge hooked up to the line going to the CSV. It showed about 8 - 9 PSI. Enough to run the engine I figured but why wasn't the fuel pressure regulator opening?
I went to remove the pressure regulator and fuel started spraying out so I knew there was lots of pressure inside of the IP.
As it turns out, 9 PSI isn't enough to open this valve and so the fuel wouldn't return to the tank. I test drove the car quite a bit over several days but it was always cold out so vapour locking wasn't a problem. Once it turned warm out, it became a big problem.
Since the pump works well enough we ended up using a 230SL regulator as a temporary fix. This style has a small hole in it which will allow for some fuel to return to the tank which is really the key to all of this. It will probably need a new fuel pump down to road but this may keep him going for the season. Removing the regulator is easy to do so we can change it back if needed.
Just one more thing to check. I've always seen some amount of fuel at the return line during any tests I've made but this is the first time I saw nothing, which made no sense on an otherwise perfectly runing engine. In this case, there was always enough fuel pressure to run the engine but not enough to open the FPR which led to vapour lock.
