Stephen Cowart

I have an 87 charokee that i cant figure out whats going on. It idles really smooth but as soon as i open the throttle even just a little bit it starts misfiring and if i open it up all the way it starts to backfire. I have had it apart and made sure the timing gears where correct and the distributor was stabbed right. I replaced the cps and tps but cant get the new tps in range. Ive refreshed the ground at the dipstick and the firewall. I cleaned the c101 and most of the connectors under the hood and dielectric greased them. I did a compression test with the manifolds off and all the plugs out and im getting about 150 psi on all with a variation of no more than 1-2 psi. ive cleaned the intake and put a new gasket on. I dont know what the problem could be. the only thing besides the brand new tps being out of adjustment is the knock sensor is busted and the plug is off. Someone told me the ecu might be bad so i took it apart and cant see anything burnt or melted.

DFlintstone

It's not the knock sensor, very unlikely the ECU. I endured that for over a year. At one point I blew the mouse nest in the air-box out the front, then drove through the confetti! (no sign of the mouse ) In my case it was one of the wires to the "lower sensors", that come off the injector harness grounding. (they were routed wrong and the heat shield edge had cut in. I fixed that and no more problem.

Later after joining the forum I un-taped my repair and tried to duplicate it to find which wire was doing it...no luck.

So it may be lean, is the consensus. Your fuel pressure should be about 29# with the vacuum line on the regulator, and about 10 more with it off. You can borrow a tester free at a big-box auto parts store.

Then as far as the lower sensors, I'd think the Engine temp sensor, or it's wires might be the first to suspect. My issue could not be the knock sensor, and I don't think the 02 has the "power" to mess with the mix that bad. Maybe test, or change the temp sensor. Look really good at those wires under there. Maybe even jiggle them while someone power brakes it.
Truth is this comes up, and often we don't end up nailing it.....

Sounds like you found Cruiser54's stuff, it's linked in my sig Btw. He says if you can't get the TPS in spec, that it's bad.

cruiser54

Verify fuel pressure with a gauge.

DFlintstone

Waz thinking, (and remembering). The puter' will ignore most of the sensors when you floor it. Mine would sputter and cough, but go like heck if I floored it.

That tells me my TPS was signaling the puter it was floored, and likely it was getting enough fuel to be able to take off like that. (get that TPS in spec so you don't need to wonder about that?)

Try it, on the floor!

cruiser54

Intake backfire is lack of fuel already.......

DFlintstone

I think my lack of fuel and intake backfire was the coolant sensor (wire) confusing the ECU. (not sure which wire it was though) Finding and fixing that grounding wire fixed it, night and day, after a year! It would launch like a rocket floored though.

Nothing against checking pressure, but if it goes like a raped ape floored, it's likely that it's getting fuel.

cruiser54

Verify fuel pressure before proceeding in other directions.

Stephen Cowart

I have already put a new fuel pump and some injectors off another jeep. I checked the pressure with a guage when the engine was not running and the pressure was good. It seems like its not advancing but i guess i should verify pressure while its running. I will post again once i get some time to rent the guage. Also when I floor it it doesnt do anything but a few times i was able to get it over 2k rpm and it ran like a beast and would rev great but i cant duplicate that anymore.

DFlintstone

MMM well Cruiser is the man. I'd ask if you think you did a good # on the c-101.......maybe double (triple) check the dizy is indexed right.

Bonehead me, I might see if it revs OK with starting fluid.

Stephen Cowart

Ok so I just got done testing the fuel pressure and it read 35psi while its running. I even pinched off the return and boosted it up to 50 psi and tried to throttle it still no change. the previous owner cut the ears off the distributor. I stabbed it correctly and since i can ive tried rotating it slightly to see if maybe that was the problem but theres no change when i rotate it until it dies.

cruiser54

Go to www.cruiser54.com and use Tips 12 and 13 to get the distributor right.

DFlintstone

Stephan, you do know that the timing is controlled by the puter. The cap just needs to be in a place where the spark from the rotor can reach an electrode. It's set with the rotor tip just leaving the electrode so as the puter advances the spark it can still reach. The distributor can't, won't, isn't, advancing the spark.

Those other lower wires on the dizzy barely mater, it will run fine with them unplugged.

When you are happy with the dizy, I'm curious how it revs with starting fluid. Thinking that could tell you if it's lean.

Stephen Cowart

Yeah I know the computer is what controls it but ive seen a lot of people say 1 tooth can make a difference. I thought about just getting a new one but I feel like I should be able to get it close enough to change the symptoms. I need to get a different cap in order to set it like it is in that write up.

cruiser54

You're on the right track.

DFlintstone

Correct me if I'm wrong. On a Renix, with the sync pulse generator unplugged (and ear sawn off)#1 could be anywhere. (like dizzys of old). Different story entirely on post 90 OBD Jeeps.