92 XJ running bad when you got to WOT?

Ok, I have a 92 XJ 4.0L Auto. I had a bad injector that was leaking replace that. But before I replace it. It start run weird. You would be driving down the road and push the gas to pick up speed and it would fall on it face. Let off the gas an push it down and some times it would take off like it was fine. Some times it would fall on it face. The other night I was on my way home and just driving down the Road it start to fall on it face drive at a normal speed. So I thought the injector was really bad So I replace it. Will it is running better but still has the problem. Thought the Cat was Clogged so I punched it out last night seem to help some but is still there.

The XJ has 198,??? miles on it. Things that have been Replace it the last month.

Cap
Rotor
plugs
wires
Coil
Fuel pump
Fuel filter
Fuel pressure Regulator
TPS
Bad Injector

Could the Cam Position Sensor cause this problem. When it acts up it sounds like it is flooded and than it cleans out and takes off just fine.
It also Start up and idles just fine. In fact now that the Fuel injector is change it starts better than it has sense I have own it. Bought it 1 1/2 months ago.

Any Ideas would be great.

Cam Position Sensor is a less likely culprit than the others, like the Crank Pos Sensor or the MAP Sensor.

If the cam position sensor was bad, the PCM would not know what phase the cam was in, and would be forced to guess at the phase, and it has a 50/50 shot of being right. Thus you have a 50/50 shot of injectors firing at the right time, and it would continue the entire time between each start. With the injectors firing 180° out of phase, the motor will run, but it will run like crap and thats the entire time, not just at WOT.

Have you checked for stored codes in the PCM? I'd correct those codes first and then start testing sensors with a multi-meter.

A 92 will through codes I suggest you have it scanned.

A '92 will give you codes by blinking them out on the "Check Engine Light", will it not? Try that first, turn the key on/off/on/off/on within 5 seconds, the CEL should start blinking, count the blinks, it will pause between numbers. Arrange the numbers in 2 digit codes and that should be your codes. Code 55 is end of test.

The 2 digit codes blinked out by the CEL are more general and usually 1 two digit code covers several of the more definitive 4 digit codes stored in the PCM. So, depending on what code you get, you may need to take it to Auto-Zone and have them do a scan for the 4 digit codes.

Well reading the codes will tell you what the result of whats going wrong, not nessacerly whats causeing the problem. It is a good place to start. Also if you can backprobe the TPS sensor and see what its readings are Key on engine off. You might have an issue in the TPS circuit or even the PCM if somthing is really wrong. Check the power, ground, and signal @ the TPS if all are good then you need to look at your grounds then other sensors can become suspect like the Crank Position Sensor. Hope all this helps.

Thanks for the help. Last night we unpluged the Map an it ran like crap all the time. But it ran like it did when it would mess up too. So I was thinking maybe the map was acting up. I will check codes tonight. And If I can not get anything that jumps out I will take it to Auto-zone. Is there some where I can get a print out of Codes for a 92XJ?

Ok well the autozone in Monroe Michigan will pull codes on a Truck that OLD. Wife Ran it up there on her way to school. She said it acted up on her 2 times in about 20 miles. She went press the gas pedal to the floor 3 times and she said it clean out and took off fine. There was a guy there that said it might be Clogged injectors.

Well on her way to school doing 45 mph. It started acting up. It was shuttering and would not clear out. after a few mins it did and it took off. I am going to go up to the school tonight an get it. Drive it home an pull codes with the key.

Something to keep in mind.

If it only does this during WOT, but from your description you seem to indicate it happens in other conditions as well, the computer goes into a seperate mode when you go WOT.

When the engine is warmed up and at idle or part throttle the PCM is in Closed Loop mode, when the engine is cold or at WOT, it is in Open Loop mode.

Closed Loop means the feedback loop of the O2 sensor is closed and the computer is using feedback from the O2 sensor to maintain a 14.7:1 A/F ratio as close to possible. The PCM will store correction values that it applies to fuel tables stored in it, basically the fuel tables are for a perfect baseline engine, no engine is perfect and it needs change with wear and age, so the computer is constantly measuring how close the orginal fuel table is to the actual fuel needed and how much of a correction was needed from the feedback from the O2 sensor. Simplefied; the PCM uses the O2 sensor to constantly TUNE the motor.

Those correction values will be used to correct the fuel tables for OPEN LOOP Mode as well.

When the motor is cold or your at WOT, the 14.7:1 A/F ratio is no good, you need a much richer A/F ratio. Problem is, the O2 sensor is only good to measure a 14.7:1 A/F ratio, its extrordinarily inaccurate on either side of 14.7:1. So when the motor is cold or at WOT, the O2 sensor is worthless, and the PCM opens the feedback loop and just runs off the preset fuel tables. BUT, the PCM applies corrections to the fuel table for OPEN LOOP Mode that it learned in CLOSED LOOP Mode.

So, if your only getting problems at WOT, there may be some sort of problem with the PCM switching back and forth between OPEN LOOP and CLOSED LOOP Modes, maybe the PCM doesn't realize your at WOT and is still in Closed Loop Mode? A bad or improperly installed TPS could cause that. Maybe there is something going on in closed loop that is messing up correction tables, but the PCM can recover with the O2 sensor, but can't recover when in OPEN LOOP without the O2 sensor. Could an O2 sensor be bad?

I'd first get those fault codes stored in the PCM.

You said you replaced only ONE injector. Have you thought about replacing all the others? Since you had one bad injector, there's a good chance the others are knackered as well.

Yes, I have thought about replacing the other ones. Last night I drove it around and it is acting more like it is running out of gas. I started thinking when did it start running like this. It start Friday evening. I had to stop on my way home and put gas in it. It started acting like this on the way home after I stop and got gas. I am think I might have got some bad gas. So tonight I am going to empty the tank and put is some new gas and see if that helps.

I pulled Codes and got
11 I replaced the coil a week or two ago
22
15 I knew I would get this one. My speedo does not always work.
27 I replace the Fuel injector that was leaking.
14 I unhooked the Map sensor to see if it ran the same or worse. (it ran worse)
23
24 I replace this about 3 weeks ago.
55 I know this means it was done telling me codes.

I have not cleared the codes at all on this truck. And this is the first time I pulled codes.

I had a 95 YJ 4.0L, it did the same thing. It was the CPS. Get a new one. Your problem will go away.

A bad CPS will cause the engine to stall right out of the blue rather than splutter. Spluttering is more indicative of a fuel delivery problem (faulty fuel pump, blocked fuel filter, clogged injectors).
I still think that replacing the other injectors will probably cure the problem. As I said, if one injector is bad it's likely the others are also bad, especially if they've done nearly 200k miles.

I cleared the codes last night an started it back up. Ran like Crap. Got Code 12? What is that.

I am thinking CPS or Injectors also.

Thanks for all the help.

Code 12 just means battery disconnected within the last 50 starts.

Code 12 is "Battery Disconnected within the Last 50 Starts". Its very common, my theory is that if your battery is a little bit weak, it will drop in voltage enough during start that it will trigger that code.

You should get that code anytime you clear the PCM, because you cut battery power to it. Either pulling the battery cable or pulling the fuse for the PCM (Most Chrysler vehicles the PCM shares the fuse with the Fuel Pump).

Plenty of people get that code and the battery runs great for years. AS well, it seems anytime you have trouble codes a code 12 is there also. I've seen some people say the Code 12 also means beginning of codes as well as battery disconnected, like Code 55 means end of codes.

You'll have to drive it a while and see if you get the codes back.

Remember, like mentioned, the code only tells you what the computer sees, you can have a shorted or broken wire to a sensor or device that makes the code trip and theres nothing wrong with the sensor or device.

Some things to also consider;
*Look over the wiring for the sensors/devices, like the fuel injectors that you got codes for, there could be an short or an "INTERMITTENT" short that is causing your problem. Check the wires at the connectors with a multi-meter.

*Check fuel pressure, the fuel pump could be going and there is no sensor for fuel pressure, the PCM can adjust for low fuel pressure during low engine demand, but as soon as demand exceeds what the weak fuel pump can provide, the engine would fall on its face. The low fuel pressure would cause strange responses from other sensors and you can get erronous codes for other sensors/devices. You'd have to borrow or buy a fuel pressure gauge and hook it up to the fuel rail and check it.

I had an intermittent short in a fuel injector on my Neon R/T. It got progressively worse until it was constantly shorted and that blew the fuse for my PCM killing the motor. I almost replaced the fuel pump, but I checked the fuel pressure and it was normal, so checked the wiring with a Multi-Meter, half the injector connections had Continuity with ground (normal) and the other half had infinite resistance (Switched Open) EXCEPT ONE, it had 100 ohms of resistance. I unwrapped the harness and sure enough, found a chaffed wires that would make some contact has the wire harness was tugged with engine movement and rocking. That would short the injector, give me all sorts of codes related to the injectors and the engine would fall on its face for a few seconds until the wires unshorted.

All I had to do was fix the short and it ran great, no more codes. Sometimes you can just wrap the short in electric tape, my shorted wires were so bad (some melted and cooked in half, barely hanging from a thread) that I had to cut sections out and solder in new wire, which I slipped shrink wrap over the wires when I trimmed out the bad sections, and wrapped them in electric tape after that.

Well that sucks. The Jeep was running like crap. It was missing and not running right. Last night I was driving it around trying to get a fell of what it was doing. I turn around on the road and went to WOT and it Jump and ran great for 5 secs. and Than fell on it face!!! but for that 5 Secs or so it ran like it should and than just lost all power and start missing like mad. Played with the gas pedal and it start to drive better but could not push the pedal pass 1/4 throttle with out it missing again.

Also On a side note, I was thinking Fuel last night also. I took the fuel filter out. And I had my friend turn the key to the run position an the fuel pump did not turn on. I put a fuel tube in place of where the filter was and started the Jeep. It start up and ran. We took it for a ride. It drove like it did before. We turn the key on 2 or 3 times with out the fuel line connected and the pump did not turn on.

Did you crank the motor while the filter/tube was disconnected?

A safety provision in the PCM, in case your in a wreck and the fuel line is broken open, you don't want the electric fuel pump to continue to run on battery power and pump fuel out of the broken fuel line, it won't run the fuel pump if the PCM senses that there is no engine rpm.

It will only run the pump for a second or two when you first turn the key to prime the lines, then it won't come again until you crank the motor and PCM senses RPM.

So why didn't the Fuel Pump Come on for a second or two to prime the lines when the filter/tube was disconnected? I'm not sure, I think there are additional safety provisions in the PCM for roll-over, I think it uses the emissions vapor system, that has a pressure sensor and taps into the roll-over vent/valves on the top of the fuel tank. I'm not sure how it works, but I'm guessing the PCM can tell when the lines are opened up and the tank is unsealed or empty, using the pressures in the vapor recovery system for emmissions, and thus won't turn on the fuel pump until the system passes that test.

I really really doubt the fact that the fuel pump would NOT turn on while the filter/tube was disconnected has anything to do with your problem. If you think the fuel pump may be bad, check the fuel pressure, that will give you a REAL INDICATION as too what condition the pump is in, not the fact the pump wouldn't turn on with open lines. It turned on and ran fine with the lines connected didn't it?

Your symptoms are really sounding like it COULD be a short in the wire harness to one of the fuel injectors, or maybe a short to the ignition or a sensor. I'd start looking for shorts as well.

I am going to be looking at the harness this weekend. Thanks for all the help. I do not think the fuel pump would be bad. the Fuel pump is a month old. Aless I would hope it is not bad. I have seen like that happen though. And that does make sense with the pump not coming on. Because with the line connected it started right up.

All fixed. Turns out it was the hose in the gas tank. It was leaking. Thanks for all the input. This is a great side for info.

Tweeternpi