Jeep engine problems

[jfrabat]

OK, guys; after undoing the TB swap because of all the engine problems that I was having, I decided to take some measurements (fuel pressure and vacuum). Please help me diagnose the symptoms of my jeep!

Symptoms
When engine is first started, it "lops" for a couple of cycles, then turns on the CHECK ENGINE light and the throttle smooths out. When the air conditioner compressor comes on, the idle drops dramatically, and the Jeep stalls or comes close to it.

I tried "reading" the code, and it looks like 12, 13, 55; but the spacing is so odd, that I am not sure that is what I am reading (I got a short video in case anyone is interested in reading it for me; just le me know your e-mail address and I will send it - it's about 330Kb). In any case, I got a OBD1 code reader compatible with Jeep arriving tomorow, so that should clear one part of the problem up!

The next symptom is that the engine will not rev past 4,000 RPMs. Once it reaches that figure, it drops to about 3,500 RPMs, and continues in that cycle until you stop giving it gas. It does this both in gear and in neutral.

With the engine hot, when you give it gas, the engine stalls. You have to stop giving it gas and the engine comes back to life (sometimes!). To accelarate, you have to SLOOOOOWLY bring the RPMs up.

Measurements

I decided to measure fuel pressure and vacuum, as these sounded like the most obvious places to find a problem (other than the ECU, which I cannot yet read).

The vacuum readings were OK, with the idle measurement being fairly steady at 17 in/Hg, and going up to 20 in/Hg (again, steady) at 2,000 RPMs. As I understand it, this is indicative of a good functioning engine.

The fuel readings, however, were a totally different subject. Instead of the pressure coming up to 31 PSI as it should when the ignition is turned on, it only came up to 25, and the pressure dropped slowly to 20 within a minute (the ignition was still on). When the engine was turned on, the pressure needle started dancing wbetween 42 and 45 PSI. If I revved up the engine, the pressure would steady up at 44, then drop to 42 when I stoped giving it gas, then it would start dancing again. When I shut off the engine, the rpessure slowly dropped to 26, and then it continued dropping, but at a slow rate.

Any thoughts on this?

All your kind help is much appreciated!

Felipe

 

[jfrabat]

Finally received the computer, and basically, it was agreeing with what some of you said online; lose vacuum hose. And I guess the hard mechanical job I did yesterday (saying sorry to the jeep for calling it "car") paid off, as the jeep is running as smooth as a baby's behind now, idling at 900 RPMs and not coughing at all.

It seems that the vacuum connection that was loose was the same conection I used to conect the vacuum gauge, so when I read the gause, it showed no vacuum problems, and when I connected the hose back on, I cured the problem. I tried to go back to the 4.0L TB, but I still get high RPMs for idling (about 1,500 RPMs), so I decided to stick with the 2.5L TB until I fix the fuel system (which did show problems when tested; it seems the fuel pump is failing after working for some time, and the FPR is already toasted).

Felipe

 

[jfrabat]

Hopefully, I took care of this problem on Saturday... I dropped the tank, cleaned it out real good with POR-15 Marine Clean and a lot of water afterwards, dried the tank real good, and replaced:

Fuel pump and prefilter
Fuel filling and vent lines
A couple of fuel hoses that looked worn
Fuel filter (old one looked OK, but just in case!)
Injector rail
Fuel injectors (I put some Bosch ones in instead of the stock injectors)

Once the summer comes around, and the temps go back up, I will be able to tell if this fixed the problem or not. Since almost the entire ignition and fuel systems have been replaced, I figured the odds of it not being fixed are slim, right? It's probably overkill, but I wanted to be sure none of these systems would fail in a good couple of years, so I think it was well worth it. Plus, I did it myself, so it was not exceedingly expensive (not after finding the best deals online for each product, anyway!).

I think I will now give the 4.0L TB a second chance, and see if I can get the Jeep to idle propperly. After that, I will also measure the compresion of each cylinder to make sure there are no problems there,,,

Felipe

 

[TwistedCU]

This 4.0 TB has turned into quite the project!!! At least you fixed the aging fuel system parts before they failed out altogether. I hope it works for you this time.

 

[jfrabat]

Yeah, well, I do want to keep this Jeep for a good couple of years, so I would have ended up doing the fuel system sooner or later... Might as well get it out of the way, right?

 

[redrooster]

FYI... on a chevrolet throttle body, there is a process for resetting the Idle Air Control motor. I don't recall exactly what it is, but there should also be a process for the Jeep throttle body.
It is something like unplugging the IAC and threading the plunger all the way in. Then you hook it back up and turn the ignition on (without cranking)to let it thread the plunger back to where it needs to be against the throttle body.
The gap between the plunger and throttle body controls the air into the TBI therefore controlling the idle.

 

[jfrabat]

Rooster,

I also read online that there is an Minimum Air adjustment screw suppossed to be on the TB or intake manifold somewhere, but I have been unable to locate said screw... I am currently out of town, so I cannot recheck, but if anyone knows where it is, can you please help me?

Felipe

 

[redrooster]

Probably referring to what I was calling a plunger. I have never fooled with a Jeep fuel injection, so I can't talk specifics. It has to be similar to the chevrolet system though.