Jeep Wrangler Forum banner
  • Hey everyone! Enter your ride HERE to be a part of JUNE's Ride of the Month Challenge!

1 - 20 of 46 Posts

·
Registered
Joined
·
103 Posts
Discussion Starter · #1 ·
Title says it. '95 YJ (2.5, 4 cyl, AX5 manual) has a definite misfire and I'm pretty sure it's multiple cylinder. The Jeep seems to be WAY down on power. I can't keep up 55 on a hill in 4th gear. No matter what gear when I try to accelerate unless I am very high in the RPM range it sputters/misfires badly and sometimes backfires. The problem shows itself either when taking off slow or from a complete stop, when trying to accelerate in a "high" gear, or when trying to keep up any speed up a hill in any reasonable gear.

I've replaced several parts trying to track down the issue. IAC was replaced, Catalytic converter replaced, TPS replaced, Checked cap, rotor, and distributor, look very clean as do the plugs and wires.

Fuel pressure at the rail is good, throttle position sensor is good, both tested using the methods in the FSM. There has never been a check engine light on in the dash, I do know that the bulb works. I also tried a full tank of 93 octane gas, and I think it made the problem worse, but definitely didn't help.

My next checks are to replace the dizzy cap, plugs, and wires, since I know they can cause this issue and are cheap. I'm going to visually check and test the O2 sensor, and try and figure a way to test the intake/exhaust manifold gasket. I'm assuming I can't use the carb cleaner test since I'll be spraying directly on the exhaust.

So you know, yes I already started a thread about this issue but i didn't really know what was going on so to avoid confusion here is a new thread. I've asked the mods to close that thread.
 

·
Registered
Joined
·
638 Posts
Have you checked your timing chain by chance? Wonder if it jumped a tooth or 2.

Only other things I can think of (besides what you have replaced) Would be the Cam-sensor OR Crank sensor (they have both) throwing the timing off. Those USUALLY will throw a code but I've had an odd dog or 2.

Bad head gasket? Usually accompanied by excessive coolant consumption for those that don't blow the oil side.
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #3 ·
Have you checked your timing chain by chance? Wonder if it jumped a tooth or 2.

Only other things I can think of (besides what you have replaced) Would be the Cam-sensor OR Crank sensor (they have both) throwing the timing off. Those USUALLY will throw a code but I've had an odd dog or 2.

Bad head gasket? Usually accompanied by excessive coolant consumption for those that don't blow the oil side.
Nope haven't checked the timing chain. I did go out again and really listen to the engine... it really sounds like it's dieseling (pinging) like it's firing late or early. Coolant level hasn't changed and have no heat problems and the oil is clean and doesn't smell. I'll have to look up the CPS & CKP testing procedures.
 

·
Premium Member
Joined
·
10,093 Posts
Dirty injectors and carbon in the head.

Try some injector cleaner your choice in the brand double the recommended strength first tank. Or remove the injectors and clean manually using a scribe or dental pick to get carbon off.

Go to google put in read spark plugs a picture comes up with a chart of plugs and compare yours and see what that tells you.

It's misfiring at different times on different cylinders fouled injectors.

Best I got
 

·
Registered
Joined
·
63 Posts
if it backfires that is down to timing, run it at night and look around plugs, leads, distributor for any signs of spark tracking.
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #6 ·
if it backfires that is down to timing, run it at night and look around plugs, leads, distributor for any signs of spark tracking.
I'm changing the plus wires rotor and cap tonight hopefully it helps. If not then I'll be reading the rest of the sensors.
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #7 ·
The problem that still throws me off is that it does not have the issue under load in reverse. It makes me think a sensor because if it was a purely mechanical problem it works do it regardless of forward or backward. If I take off in first gear it mis fires, but taking off from the exact same spot in reverse the engine runs beautifully.

Am I over thinking this? Is it not that wierd to happen like that?
 

·
Registered
Joined
·
303 Posts
IIRC vacuum advanced only works in forward gears which would indicate a timing issue. With all posts above I am lead to believe your timing is about an 1/8 to a 1/4 off. You said you thought you heard pinging, like piston slap or pre-ignition?
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #9 ·
IIRC vacuum advanced only works in forward gears which would indicate a timing issue. With all posts above I am lead to believe your timing is about an 1/8 to a 1/4 off. You said you thought you heard pinging, like piston slap or pre-ignition?
So then it is probably the timing chain or one of the sensors related to timing?
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #10 ·
IIRC vacuum advanced only works in forward gears which would indicate a timing issue. With all posts above I am lead to believe your timing is about an 1/8 to a 1/4 off. You said you thought you heard pinging, like piston slap or pre-ignition?
And no I didn't really hear pinging when I was driving but I definitely heard it when it was just started and idling.

It really sounded like a diesel motor. Like the knocking sound an idling diesel makes but not quite as pronounced. I'm thinking this would I indicate a late fire (spark too late) and would also explain why the high test gas made it seem worse...

I guess I'll just plug the spark plug holes and put diesel in it!
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #11 ·
Replaced the plugs wires dizzy cap and rotor and it no longer can maintain an idle... I did find a vacuum port with a bad plug at the throttle body on an extra port so I put a new plug on it but it didn't make a change.

I visually checked all the vacuum lines I could find but nothing else appears cracked or worn.
 

·
Registered
Joined
·
303 Posts
Do you have a timing light? If not then cold time it.

Cold Time procedure;
Pull the number one spark plug.
Cycle the engine.
You will feel two rushes of air, one greater than the other. ( This is compression )
Continue cycling the engine until you get the #1 cyclinder to top dead center.
Replace #1 spark plug.
Pull the dizzy cap. mark where dizzy seats against engine and rotor location.
Pull dizzy.
Set rotor a couple degrees off of #1 ( when inserting dizzy, rotor will rotate due to curvature of teeth )
Make certain rotor is pointed at #1 wire post.
Tighten dizzy, replace cap.
Test run.
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #13 ·
Do you have a timing light? If not then cold time it.

Cold Time procedure;
Pull the number one spark plug.
Cycle the engine.
You will feel two rushes of air, one greater than the other. ( This is compression )
Continue cycling the engine until you get the #1 cyclinder to top dead center.
Replace #1 spark plug.
Pull the dizzy cap. mark where dizzy seats against engine and rotor location.
Pull dizzy.
Set rotor a couple degrees off of #1 ( when inserting dizzy, rotor will rotate due to curvature of teeth )
Make certain rotor is pointed at #1 wire post.
Tighten dizzy, replace cap.
Test run.
According to the FSM the initial timing is set by the pcm and adjusting the distributor is not possible, and won't help a timing issue. Remember I have a 95 with computer controlled MPFI not TBI or a carb.
 

·
Registered
Joined
·
2,585 Posts
I second this, the distributor is not adjustable, timing is set by the computer. TBI and MPFI models are the same. Get a timing light on it and check the timing.
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #15 ·
I second this, the distributor is not adjustable, timing is set by the computer. TBI and MPFI models are the same. Get a timing light on it and check the timing.
I'm replacing the ckp and cps so hopefully that helps works. If not I'm done messing with it and taking it to a shop for diagnostics, although at this point the only other thing that could have happened is the timing chain skipping a tooth.
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #17 ·
Update... ckp, iac, tps, coil, dizzy cap, stator, rotor, plugs, wires, fuel filter, all changed... the jeep runs worse than ever..
 

·
Registered
Joined
·
103 Posts
Discussion Starter · #18 ·
I'm about to just try and get it to start and run it as fast as it will go into a tree, but I honestly don't think it can go fast enough to damage it.
 
1 - 20 of 46 Posts
Top