This is my first thread, I recently purchased my first jeep, 1990 xj 4.0
It will idle fine, but after 15-20 sec. of driving, it starts spitting, sputtering, and back firing. But only when I'm giving it gas. It idles just fine and I can barely tap the gas and keep it driving but anything other than a light tap and it will start to die. I have an emissions maintenance light.
It has new plugs, wires, cap, rotor, button, injector o-rings, air filter, TPS, absolute pressure sensor, the sensor beside the TPS, starter, alternator, header, head gasket, and a few other irrelevant parts. PO wallet bombed it and now I need to fix their mess. I'm going to try the O2 sensor first, then go from there. Any help would be appreciated!!

 

Welcome.

The maintenance light is just a timer. Disregard it.

Have you tested the fuel pressure?

I love the term "wallet bombed" by the way.

Go to www.cruiser54.com and complete Tips 1,3,4, and 5. We'll get this figured out......

TPS is adjustable also. who knows if they did it?

 

Welcome!!! ^^^Listen to this guy man, he knows his stuff so much even his stuff knows he knows his stuff

No seriously though, he's the Renix guru, he'll take care of ya.

 

I just reset the TSP by backprobing the connector, i had 4.81 and set my output to .81. still doing the same thing. ground stud by dipstick is clean and secured, firing on all 6 wires

 

Gotta test fuel pressure as Cruiser54 recommended. It's top on the list of ruling in or out. For a 90, you should have 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Check that vacuum line for rot and it should not have raw fuel in it, which would be a sign of a ruptured fuel pressure regulator.

 

all vaccuum lines are new, and regulator is not ruptured. im going to borrow a fuel pressure gauge from advance auto parts and check that next

 

Did you clean it or just look at it?

 

The ground stud?

 

Yup

 

It's shiny and nothing is loose, the motor was hot so I didn't dig into that too much. I will dis-assemble it this evening and wire brush it. It's also overheating, PO said it needed to be burped?

 

It should self burp if the cap on the pressure bottle is good.

 

It bubbles and gurgles a lot but once it starts doing that I shut it off. I also ruled out a clogged exhaust. The only problem I was told it had when I bought it was it wouldn't go over 60

 

How did you rule out clogged exhaust?

Cruiser’s Vacuum Test for Exhaust Restriction

Your vacuum gauge should come with an instruction booklet outlining this procedure.

Hook the vacuum gauge up to a source on the intake manifold.
Start the engine and note the vacuum reading.
It’s usually 17 to 21 inches of vacuum.

Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle.

Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading.

If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.


Get a Napa 703-139six cap. The key for six just stuck on my keyboard!!!

 

Well I disconnected the glass pack and looked in to with a flashlight, both ways, I read the cat can cause problems with the baffles rusting out, but that's already been replaced. Hence the glass pack. I'll check it with a gauge today like u said. Thank you for your help sir