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Engine barely running, Bad gas perhaps?

2K views 19 replies 6 participants last post by  Dadwrench 
#1 ·
I have 2 jeep cherokees that i have turned into one. The first is a 93 4x4 auto with 4.0 that always ran great up until the very last time i ran it. It started right up ran fine then died and didnt want to start. Parked it, my cousin tried to drive it and it did the same thing started ran fine then just died and wouldnt start again. I got a 96 jeep in alot better shape just needed a motor. The 96 had a full tank of gas in it when i bought it, i did siphon some gas out of it to move the 93 before it started the problem. Now the same engine is in the 96 got it running. I have to give it gas for it to start, it wont idle on its own, revs up and cuts out, just runs horrible. The intake and all sensors on it are from the 96 including injectors and all. Plugs and wires are from the 93. Does this sound like bad fuel? Sensors? Plugs, wires? Any help appreciated! If i drain some gas into a clear glass what should I look for to see if its bad?
 
#4 ·
Sounds like an intake leak for starters, and if the check engine light is on, I am sure that would shed some light on the problem.
The 96 could have had a bad PCM also, as you dont know why it was parked other than a bad engine. Usually cars are abandoned when they have multiple issues that the owner cant seem to overcome. :(
If that has a non return fuel system it could be airlocked at the fuel rail also, you could try bleeding the air off,if any is present to see if that helps.
 
#5 ·
The only thing I cant figure out is its the same motor that was in the 93 and it did basically the same thing the last time i ran it. The only thing that ties the two tegether is timing, fuel, plugs, wires, distributor, coil. Also i put a new intake gasket on it
 
#6 ·
Another thing... if i hold it at steady idle it will clear up for a second then you can tell its like the computer is trying compensate for something it will start to stall then rev back up while holding gas pedal steady. i got it to idle on its own once then it started to rev then I shut it off. And the owner did tell me they had put two engines in due to overheating, but never said anything about it running roughly. I dont know if that would be of any consern.
 
#8 ·
Maybe you need to check your grounds. Sounds like a few are missing. If the tach is "dancing" while cranking or running that is a good indication of a poorly grounded body/frame/engine.Also could be a defective PCM
Go back over the wiring/grounds/add any grounds you had from either vehicle. Too many wont hurt anything.
Then check for an airlock in the fuel system
Then check fuel pressure
If the check engine light is on, scan it for codes
Proceed from there,good luck
 
#9 ·
The 96 model is a full OBDII system. I'm assuming that the distributor is from the 96 model, correct? If the tach is bouncing, that would indicate a bad crank sensor. This would be located on the left top of the trans bell housing in line with the flywheel (crank reference picked up by sensor from flywheel). If you slide your arm along the seem between the engine and trans from underneath, you can feel it. It's close to the top. Many times I have seen the harness to this sensor shorted due to the tight quarters where it is located. You need to plug in a scan tool and watch the engine RPM while it is running. You can make a failing sensor still work if you increase the engine speed, but the wave form delivered to the ECM degrades as the engine speed drops. It has been a while since I dealt with this problem, so It may be in the block and not the trans, however the location is right where the trans bell housing and the block connect. I have replaced a large # of these over the years. I have found that they usually fail worse as the engine heats up.

As for a fuel quality issue, here is what I do. Smell the fuel first. As gas degrades, it will start to smell like varnish.
Stick the tip of a long shaft screw driver into the fuel and then try to light the tip of the screw driver. It should ignite violently. NOW LISTEN CAREFULLY! DO THIS OUTSIDE AND YOU MIGHT NOT WANT TO BE HOLDING ONTO IT. IN OTHERWARDS, DON'T TRY THIS AT HOME! As the octane is lost from age it will be very hard to ignite. Compare it with some known good fuel if you want to be sure. I CAN AND WILL NOT BE RESPONSIBLE IF YOU BURN YOUSELF, THE VEHICLE OR YOUR HOME!!!! :p GOOD LUCK
 
#10 ·
The distributor is out of the 93, the wiring plugs were the same... should i install the one from the 96? I replaced the cps on the 93 not long ago so I will swap those and see if that clears anything up. As for the fuel I will try your suggestion, if there is water in the gas it should be hard to ignite too, right?
 
#11 ·
Sounds to me like you have a vacuum leak. Do you have access to a scanner. If so take a look at the fuel trims. The original issue of running and dying then restarting later is a classic CPS issue. These also can get damaged when changing an engine if not careful.
 
#13 · (Edited)
Idle issue

The problem may be allot simpler than it appears. You need to be certain that everything for "power train management" is from the 96 model. The 93 is OBDI and the 96 is OBDII. It is possible that the distributors are of the same design, but I believe the injector reference signal comes from the distributor. I would call a parts store and see if the same part # distributor is used for both models. As far as the crank sensor goes, it has an adjustable air gap between the tip of the sensor and the fly wheel, thus the slotted bolt hole in the sensor. It needs just a little more than 1/16" clearance. A new sensor comes with a paper or plastic spacer glued to the nose of the sensor to provide the correct clearance. After a new sensor is installed, the rotating flywheel scrubs this spacer off. If you are installing a used "known good" sensor, glue a piece of cardboard about the right thickness with rubber cement to provide an adequate gap.

If the engine starts and runs well except for idle then you need to identify an actual "idle problem". There is an idle control valve on the throttle body. It could be sticking. I would try removing and cleaning it first. Another possibility is a TPS (throttle position sensor). This however will usually cause the engine to stumble when the throttle is opened.

Does it actually run well when it is cold? We may be trying to hard to identify a rather simple problem. I agree with the other responses about a vacuum leak, especially if there is not enough vacuum for the brake booster to work.

As far as water in the fuel, it would most likely not start, especially when cold. You can pick up some "fuel system dryer" at any parts store to dump in the tank.

In summary, I would verify that the distributor is correct, and then look for vacuum leaks. From what you are describing, a massive leak could cause this and you should be able to hear it. However a vacuum leak will cause the idle to always run high.

One other question. Isn't the distributor adjustable and did you time it properly?
 
#14 · (Edited)
suggestions

The suggestions I Just made would not explain the tach needle bouncing. I may have gotten carried away sent you on a wild goose chase. I would still take a look at the sensor and wiring. I would fix the "bouncing" tach needle first. If this doesn't fix it then you have more problems.

One word of advice. don't change any additional parts then the ones needed to provide significant improvement. You really need to look at the codes and engine data with a scan tool. We all coould provide much better advice with this information. Keep at it and let me know what happens. We will make :D it behave!
 
#15 ·
Does the 93 have the same intake manifold.

I had a 93 4x4.the seals on the injectors dry out.

A cheap way to take vacuum leak out of the equation,is to get a can of carb cleaner,spray it around the intake manifold in most likely spots

if it surges its leaking ,TB housing cracks some times or a bad TB sensor.

There is a hole in the TBH it needs cleaned carb cleaner

The pic shows the sensor ,IAC ,and the place to clean,or take the one off the 96 motor and put on to see if it makes a diff.

Just suggestions, but take from them what makes sense IAC makes sense to a degree
 

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#16 ·
I looked up the part numbers for the distributors and they are different so I will switch them next time I work on it. As for timing it, it ran well in the previous jeep and nothing was changed... The jeep never runs good, not cold, hot, idle, mid throttle, full throttle. The intake, all sensors on it, injectors and fuel rail are all from the 96. Antoher question, if I track it down to possibly being a bad pcm, could I try the computer from the 93 if using the distributor from it also?
 
#17 · (Edited)
keep it simple.

Did you stop your tach needle from bouncing? You need a known good crank sensor or fix a wiring problem. Isn't the distributor adjustable on this model? Incorrect base ignition timing will cause all types of "drivability" issues, including but not limited to; hard starts, rough running, a "hunting" idle, and or backfiring. Fix the rpm reference problem and be certain the "correct" distributor is set up right first. Slow down and methodically handle these things one at a time. If you move too fast, you can create a new problem without fixing the initial cause of your troubles. Don't worry about the ECM yet, but no the two ECMs are not compatible. The 93 will not work in the 96 model.
 
#18 ·
I havent had time to work on it yet, i plan on changing the distributor first when I do. It is not adjustable, just set at zero and the computer does the rest to my knowledge. (correct me if im wrong). I looked up more part numbers, the coil and oil press sensor are different also. Should I swap them out for the correct ones also, or would it make a difference?
 
#19 ·
Did you do a vacuum test on it yet see what it draws.

My jeep acted up and then cleaned the throttle body.

Copyed this off another site.

1. vacuum leak.
2. bad return or power to the MAP...check for stretched or broken wires, connectors and at the PCM
3. a faulty, but not broken completely, TPS will trick the pcm into throwing a map fault.
 
#20 ·
Tach reference.

The coil could have a significant effect on performance quality. Can't make a judgment on the oil pressure switch without seeing a wiring diagram for both systems. Neither one of these would make your tach reading bounce. This is a known problem (an verifiable fault). Fix what you find that is broken and it may fix it. You do need to be sure that all the powertrain management components are from the 96 model. If you aren't sure, compare part #s for replacement parts and be sure it all fits for the 96. I do have one question though. The tach needle actually really bounces and doesn't just follow fluctuations in engine speed, right?
 
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