Rough Running


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Islington London England
I need a bit of help diagnosing what could be wrong with the running of my E9

The engine is a 535i 3430cc 1989. Originally the car was not EFI so I fitted a swirl tank and all was well with the car. I then moved to Tanks Inc in tank Walbro with built in baffle. All was well. Among the work I completed was to replace all the injectors and rubbers eliminating a number of vacuum leaks along the way.

Then things started to play up. The car would start but when hot in traffic, it would mis fire, display the symptoms of a faulty fuel pressure regulator valve - hesitation when accelerating etc., I replaced the FPR twice to no avail.

Faulty pump? I took the Tanks Inc module out and noticed some of the sealant they recommend was washing around the bottom of the tank which I cleaned out. I had a spare Bosch 044 so removed the old Walbro - fixed a plain pickup and put the Bosch in line underneath the car beside the rear right wheel. I also changed the fuel filter. The Bosch is very noisy and sounds like a gaggle of geese hissing, but I thought that any concerns about fuel pressure will go away.

So what now? Now it is lumpy and misfires when cold although it starts OK. It has the same fuel starvation issues. Once its warm the engine runs fine and is responsive and smooth. After a while sat in traffic, it starts to misfire again, and the fuel starvation seems the same. The temperature gauge never moves above mid way point.

Things I think I need to do.

Test the temperature sender - next on the list.
I have a stainless steel exhaust that cooks the rubber drivetrain components so part of the solution was to have the exhaust wrapped. There is a section of rubber fuel hose from the tank, through the pump and then to just in front of the rear wheels, picking up a metal feed after that. Could this section expand if it is heated causing the fuel starvation? In stead of cooking the drivetrain, it might be cooking the fuel pipe. It seems warm but not too hot to touch. I have some steel braided hose which might work.

I am wondering whether I have two issues rather than one. One when the engine is cold, and another when the body and attached bits under the car heat up. Does anyone have any other ideas or tests I can do. Any help gratefully accepted.