I need some help to track down the problem.

I run a 383 speed density tuned port in my rock crawling jeep and the engine stumbles when i come to a stop or let off the gas. It idles real ruff and then stabilizes. It idles just fine when i start it and let it sit. It started this last year and it is at the point of almost stalling. The jeep only gets driven about 1000 miles a year.

This weekend it was pretty bad, so i checked the fuel pressure at the rail and i had 60psi with the new pump that i installed this winter. So what do i check next. I am thinking it is the IAC or the TPS but I'm not sure how to check. I don't want to go out and just start replacing sensors.

Thanks

 

The fuel pressure might be part of it as if im not mistaken isnt like 50 or 55 psi the max you should ever do under any circumstances on a TPI system? Considering 43 psi is stock tpi 60 psi is a pretty big increase. If you really have to crank it up that high to keep your a/f ratio correct you should swap to larger injectors. You may have damaged the injectors.

 

I have never adjusted the pressure and it used to run just fine. I already have 30lb injectors and the computer was tuned for them when i first got the system together.

Here is a dumb question. Is the pressure at the shreader valve before or after the regulator?

 

Well still i think that pressure is a bit high. Especially if you never adjusted it factory pressure regulators should run roughly 43. Thing is it may work for a while at 60 PSI but it takes effort to open fuel injectors and to open an injector against roughly 20 psi more than factor and i think like 10 PSI more than they were ever designed to deal with may put a bit of a strain on them and may have caused them to fail prematurely. Also if you never adjusted the pressure it may be that you used to be running around 43 PSI fuel pressure and now due to a defective regulator or a plugged return line has caused the pressure to spike to 60 psi. If you were running 43 PSI and something failed causing the pressure to increase to 60 PSI would cause it to run a bit rich assuming the ECM couldn't compensate for it. Obviously this would cause some drive ability issues. Is it an adjustable pressure regulator? If so do you know what it was set at originally? The shrader valve is after the regulator.

 

I agree with you that the pressure is too high. For some reason i thought that was the reading before the regulator. I did chek it at some point last year and it was 43
psi. So there is either a problem with the regulator or return line.

I recently switched from an inline pump (went through 2 in 2 years) to in tank pump and it makes some strange noises when i first turn the key on. Almost sounds like air and maybe there is a problem with the return line in the tank.

 

Yea it very well could be as the way this type of pressure regulator works is by in essence having a controlled leak back to the take to bleed off excess pressure. If the return line was plugged theres no where to go besides the injectors and in many cases also through the fuel pressure regulator diaphragm. I would check for gas in the fuel pressure regulators vacuum line and maybe even remove the return line from the fuel pressure regulator and put a new one on the drains into a spare gas tank. If the pressure improves you have a bad return line. Could also be a bad regulator though.

 

i bet a 3rd gen lifted all out rock climber with 38" mickey Thompson tires would kick a$$. i can see it now. almost like a Roseanne sitcom.

 

Well I've changed the regulator to a Mallory adjustable and I changed the outed the diaphragm and am still getting 60-70psi at the rail when running. I was able to get the pressure to drop to about 58psi with the adjustment screw backed out and i mean to the point of it falling out...

I disconnected the return line also and even ran it with the return line in a jug to make sure it wasn't the fuel tank.

So anybody have any thoughts other than buying a new gauge to make sure it is not the gauge?