Ii went over the harness to those 3 sensors all the way up to were it ties in at the valve cover connectors and wires were in good shape no wear or rubbing.I tested the o2 Iit seemed to be I spec still might be bad I guess. I tapped around the knock sensor Iit did nothing and the cts was good to go.

This thing backfires like crazy I gotta figure it out. Its fine if I drive lightly put if im push my foot down like a quarter of the way it start backfiring pow pow pow pow pow until I lift the pedal or floor it once it hits second gear itll clean up and drive as normal until im about to get to 3rd and itll do it again. It kinda seems like its at the top of every gear besides overdrive it does this I basically have to floor it untill I get to the speed I want and let off and slowly press the pedal back down to cruise.

 

Sounds like one of two things.

Either the secondary ignition is failing under a load, as in coil plugs, wires, cap, rotor.

Or it's lean firing due to lack of fuel pressure/volume under load.

 

OK, Tell you what. Mine did just that. I'm sure there could be other reasons, but mine had chafed/grounding wiring, (see photo). You can even see a little burn on the heat shield where it was grounding. I need to work now, but later I'll pull the tape and identify which wire it was that caused that, something I've been meaning to do anyway.

 

OK, the brown wire looks a bit funky, but it's the green that has the nick from the heat shield. I'll look at the diagrams later. I'll bet it's the engine coolant temp sensor, and based on what Cruiser is saying it must (have been) telling the ECU it was nutty hot. (so it would run lean....Again I got to run, I'll look at the diagrams later, also maybe see if I can duplicate the problem since it's right there.

Footnote: I could start and drive all day. It was only when I turned it off, heat migrated to the heat shield and made it expand to touch the green wire. Some trips I left it running all day! I knew it waz a heat issue. I tried ice packs on my coil and other sensors......took me about a year to find that.

 

It goes when he floors it. I gotta fall a couple trees while the wind and humidity are right. I want to try grounding that green, see what that does. (funny that, "grounding the green") I mean the wire, not the trees!

 

Ill double check those wires tomorrow I think I might just order up a CTS. im not one for just throwin parts at something without knowin itll fix it but hey ill give it a shot.

I did pulk the plugs earlier today they were black they got about 600 miles on em

 

How can I test fuel pressure under load?

I might try new wires also I bought some chincy cheap ones from AZ kinda feel as if there not tight enough around the plugs.

 

Drive with the gauge attached.

Sooty plugs hint at overfueling though.

MAP, MAP hose, sensor grounds. Post 5.

 

OK, I'm sort of on my own horse over here, but the symptoms I had match yours so well...After a long look at the FSM and two other different diagrams, not only could I not find the engine coolant sensor, I also found no green, or light green that might be there. (I only found temp senders, for a gauge or a light)

Along with that, I put a needle in that nick and grounded it without duplicating the bogging/backfire. Well duh, it's cold in open loop. Warmed it up a bit and still no duplication. It was always hot, at temp, before, so I'll need to try it after a hill climb I guess.

Pete, does your "magic book", show the color codes for the gang there to the lower sensors? I see the (shielded) knock, a Black, Orange, Brn/White stripe, Tan, and a light green.

 

Which magic book? The hand written one or the service manual?

 

I'd pull the whole works off. It's common it breaks off in the rubber plug, so be careful, or you may need to remove the plug and extract the broken piece with a small screw or something. Then pick up some small vacuum line. You can heat and bend the remaining sections of rigid line to make the 90* "L" at the plug. I did it with a lighter, but a heat gun would be better. The small tube will melt easy! My fit in the vacuum line did not feel tight enough, so I put RTV black silicone, only on the tube. (so there is no chance it will end up blocking it). Napa, (and presumably others), stock small tube used for air shocks. I'm not sure of the size or if It can take engine temps though. I just used the good tube I had left.

That MAP line being perfect is crucial for the fuel/air mix. Blocked, the ECU will not get the message to dump more fuel. Leaking it will run rich, thinking you have your foot in it.

 

Ok im gonna get a new map sensor andand take this hose off and see I Iits clogged.

Thanks for the help everybody.
Ill let you know what happens when I get a new map.

 

Noticed something today, it was really cold and wet here today in good ole flint, mi. I started her up this morning and drove her and it seemed to be driving better no backfiring at all wich is unusual for her lol. Still missing sort of tho but then it eventually got worse.

Im gonna replace my dipstick tube wires atkeast 6 inches will using really good butt connectors work or do I have to sodder it?

 

Note from DJ
If you want to check your existing MAP sensor before you replace something that may not be defective.
Here is a link to a post with the information to a simple test:

Manifold Air Pressure or MAP testing
http://www.naxja.org/forum/showthread.php?t=1062262
What does it do? It compares ambient barometric pressure during start-up (cranking) to engine load while engine is running. The ECU computes that information and adjusts the air-fuel mixture accordingly.

See post #2 by mongolchuck for instructions.

You might be wise to keep this classic statement in mind when working on your Renix Jeep; I do when I have a problem with my 1988XJ:

RENIX Hell
http://www.naxja.org/forum/showthrea...1106274&page=2
Post # 16 by Joe Peters
The path out of Renix H*ll is paved with diagnostic stones.

 

Solder only!!!