Hi Everyone!

I have a 1996 Prelude Vtec that developed a misfire a few months ago. It did produce a code for cylinder 1 misfire. I did everything in the book to correct the problem. Nothing helped and I took it to a local race shop, they went through everything, determined it was running too lean but couldn't find the cause. They ended up using an adjustable fuel pressure regulator to increase fuel pressure. The car runs good but I'm still curious about the root cause of this problem. Here is the list of everything that has been done:

- new spark plugs/wire/rotor cap/ignitor
- new fuel injectors/filter
- egr valve & ports cleaned
- cleaned manifold & throttle body
- check for vacuum leaks
- adjusted valve lash
- check all sensors at the ECU (voltage drop tests)
- check timing belt
- fuel pressure was normal before the fix
- check injector and spark pulse with oscilloscope
- compression checked

 

Odds are the old stock fpr was leaking fuel back into the intake manifold due to a leaking diphragm. To confirm you would start the car up and rev it up and a down for a few seconds. Then pull the vacuum hose from the intake manifold nipple and smell it. If it smells like fuel it was bad.

Get another from any 90-93 accord or another prelude if it is found to be bad.

 

What did they raise the pressure to?

 

Thanks for the replies. I think the tech said they raised the fuel pressure from 39 to like 45 or higher. My buddies 2001 prelude was also in the shop at the time and they were referencing between the two and h22a4 motor on the 2001 runs at a slightly higher fuel pressure and that's what gave them the idea i think. The top half of the fuel pressure regulator is the part they changed, I guess if it is still leaking then I need to replace the bottom too. Would such a bad regulator show up on the fuel pressure test?

 

I can't say how much but some of the pressure will be bleeding off into the intake manifold via the leak and since the pressure tester is downstream it may show up on the gauge.

However, I can assure you that raising the fuel pressure from 39-45 will have no effect whatsoever on a possible misfire. If your misfire really went away as a result of swapping out the old fpr, it can really only be that it was simply bad as I say, imvho

 

Well the car definitely runs better with the modified regulator, almost no misfire at idle and no hesitation when driving which was really bad. The the lean codes are back, p0171 and p0174, but it runs ok. I guess I'm gonna have to settle with this, drive with this engine and maybe do a swap later on down the road cause the engine does have 250k on it.

 

Just for the hell of it, I would grab another from the junkyard and see if it still does it.