93 FZJ 80 losing power on highway above 2000 RPM (1 Viewer)

[Tony George]

Hello fellas
93 FZJ 80 losing power on HWY when accelerating since 2000 RPM. RPM going up and down and vehicle jerking . When applying gas slowly below 2000 RPM it rubs fine between 30-50 mph. On idle if I try to bring RPM above 2000 it goes right back down. No CEL. No starting issues. Any ideas would be appreciated. Thanks.

 

[greentruck]

Could be a plugged cat.

 

[maxamillion2345]

Could be a plugged cat.

Exactly my first thought

 

[BILT4ME]

Check your CEL to see if any codes were set to start the proper diagnosis.

 

[Squash]

How is it in reverse?
If she runs better in R check the wiring harness.
Obviously you've looked at vaccum lines and haven't screwed with the airbox, or just changed out the air filter.
Does the issue go away once the engine is warmed up?
Just asking because my 97 would do this till it reached 192 degrees.
Luckily with OBii I was able to see this trend and on a hunch replaced the ECU temperature sensor.
This is the one closest to the driver.
The other temp sensor is for your gauge.

 

[sail2fast]

I went through a long process trying to diagnose intermittent loss of power on hills. Felt like it was running on 5 cylinders, and it was. Only happened at higher RPMs. Ultimately it was a bad fuel injector, though having them bench tested did not find any of them to be bad. After eliminating other options, I finally replaced the one fuel injector that with a different looking spark plug and, bingo! problem solved.

Your problems sound different, though. Personally, I would suspect the distributor--if you could borrow a known good one that would be an easy diagnosis.

 

[OffRoadScott]

My 94 did something similar. I would double-check your wire harness to assure it has not melted and shorted out. While you are in there have the injectors cleaned. I would also recommend cleaning your TB and make sure the hole that runs over to the EGR is not plugged neither.

 

[Haspin FJ]

Also might check the fuel filter. Low or loss of power at higher rpm under load is something this could cause and may be on your PM list anyway. I replaced one with a cheap aftermarket filter as PM in an old RX7 and shortly after developed similar problems that had me throwing other parts at it until I pulled the new filter to find it had failed and couldn't blow through it like a good filter. I would also monitor fuel pressure when the issue occurs before throwing other parts at it.

 

[landtank]

Swap in a new fuel pump relay.

 

[lp2k]

she is getting old, time to fire the parts cannon

 

[LC4LIFE]

I would also make sure you are not driving uphill as that can cause significant loss of power.............that and a headwind.

 

[ProjectLover]

When you say it "goes right back down" going above 2000 RPMs at idle, do you mean it dies?
Seems like fuel/air/spark issue.

Could be a plugged cat like others have said. That also comes with sometimes backfiring, bad fuel economy, engine codes. The engine cant breathe if exhaust cant get out. You can loosen the bolts from the exhaust manifold and the precat exhaust to let some exhaust escape. If that fixes your problem then thats the issue.
Could be spark. When did you last change your plugs? Also, if you pull some plugs and look at them they can reveal other problems (fouling, running lean, etc).
Is your air filter clean or full of garbage?
Do you have a fuel pressure gauge? You can check running fuel pressure and see if thats an issue as well.

 

[Fraidenburg]

I am having the same problem on my 93. I just had the shop do a few things because I am running out of time before the upcoming Utah back country trip.

Here is what the shop did:
Air filter
Fuel Filter
oil change and filter
Cleaned the fuel injectors
PCV valve (already had a new one)

Took it up to the hills just to put some miles n it. Ran great before and started off great. When the problem started it would act like a bad throttle limiter or a total fuel cutoff at about 3k rpm. As the day went on anything above 2k rpm was dead. When the throttle was wide open the rpms would get just over 2k and it was like the fuel system would cut off and the motor died. When the rpms dropped to about 1.5k to 1.75k the motor would pick up and run up to 2k and do it over and over. While under power and parked. I can't find a melted wire or any vacuum leaks.

Searching on here has gave me a lot of mixed answers. I did stat it up last night again and it would rev up to redline no problem but I did not drive it, just let it warm up. Not sure it is a TPS but I am starting to think fuel pump. I need to drive it more but has anyone had this problem?

 

[Fraidenburg]

Just wanted to add, there is no check engine light on also.

 

[Feistl]

Is it the same symptoms under high and low load at higher RPM?
Eg at full throttle at say 1500, 2500 and 3500 how does it drive? And how does that compare to very light throttle at the same RPMs?

 

[Fraidenburg]

Everything is the same as far as under a load or not. You can slowly push the throttle to 2k or puch it fast, the result will be the same. It will still choke out above 2k.

under 2k it seams like it has plenty of power. I had zero problems in low crawling up a rocky hill. It was only when I hit the throttle to spin the tires going up.

 

[ProjectLover]

Everything is the same as far as under a load or not. You can slowly push the throttle to 2k or puch it fast, the result will be the same. It will still choke out above 2k.

under 2k it seams like it has plenty of power. I had zero problems in low crawling up a rocky hill. It was only when I hit the throttle to spin the tires going up.

Other people suggested a plugged cat for the previous poster. I would put that in your list of troubleshooting.

 

[Fraidenburg]

I don't think it is a plugged cat. I think it is more fuel related. I replaced the sending unit not too long ago and it was in sad shape. I think I have a good amount of sediment in my take or the pump is starting to fail.

After it sits for a bit it the problem stops. I drove it the other day and the problem started coming up around 4k. I shut it off and ran in the store. It was off for about 10 minutes so not really time for the cats to cool off too much.

When I drove it again it too a few minutes for the problem to come back.

If I just drive it in town at low rpm I never see the problem. The problem only starts when the motor is at a higher load for an extended amount of time. That's why I am thinking fuel related. I'll update this when I take it apart. Not this weekend but next.

 

[ProjectLover]

Here's a thread that covers some pressure diagnosis: Fuel pressure gauge question - https://forum.ih8mud.com/threads/fuel-pressure-gauge-question.804471/

 

[FZJAlaska]

Excelente advice so far. Beware the headwinds! 93 FZJ right? Keep driving, your problem will eventually become the engine racing with no ability to restrain it. Real fun on dark nights on icy roads. I suggest you change out that turbine device between the air cleaner and the throttle body. It’s got the cable with the difficult to remove plug on the end. Find a used turbine device somewhere. But the racing, uncontrolled engine experience should not be denied!