91 fj80 trouble (1 Viewer)

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Sep 20, 2005
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Hi all,
I have a 91 fj80 with a terrible miss under load.Plugs and wires are all fine,replaced fuel filter,still acts like it is starving for fuel.Rpms will come up if you accelerate slowly enough in neutral but if you tromp it it will spit and sputter.I suspected bad fuel from the start but have run deicer after warming up the truck inside a building and run injector cleaner with no luck.Have checked intake pipe for cracks and all vaccum lines and found nothing.It also will not start without a thorough preheating.I suspected an o2 sensor and ran it with right one disconnected (it ran worse) then disconnected left side,ran the same.I replaced left o2 sensor and still have same problem.I live in northern wisconsin and parts are not readily available plus the soonest I could find a place that could hook it up to a diagnostic computer was going to be two weeks.Then I fear they will change parts until they stumble on the problem.Effective but expensive and time consuming waiting for parts, Does anyone have an idea??
 
yeah checked air cleaner even tried it without it no difference,thanx
 
fj 80 troubles

I meant to mention this is my main vehicle which is why I am panicking.Driving my kids around in the m35 with no cab heat isnt an option.
 
Sprayed carb cleaner around to check for large vauum leaks around? Hooked a vacuum gauge to it?
 
Any trouble codes? It's easy to jump the codes on a 1991/92 with a paperclip and read them on the dash.

I've heard of the fuel pressure regulator causing those symptoms, but It'd be a shot in the dark without checking the codes first....

-H-
 
There is a "fuel sock" pre-filter in the gas tank on (at least) 91-92's. Can't guarantee it, but this very well may be your problem. I've known a few folks for whom this lead to the symptoms you're describing, and a few more who believe it should be changed as PM (~100k) anyway.

Good luck,

Curtis
91FJ80
 
Hltoppr said:
Any trouble codes? It's easy to jump the codes on a 1991/92 with a paperclip and read them on the dash.

I've heard of the fuel pressure regulator causing those symptoms, but It'd be a shot in the dark without checking the codes first....

-H-

1) Definitely check for codes, even if the Check Engine Light isn't on.

2) Main symptom of a bad FPR on a 3FE is hard starting when warm (and running fine otherwise, at least at first).

Curtis
 
tried the carb cleaner no change,dont have a vac taster only press tester.could be intake or vac leak will check closer,thank you
 
I am familiar with the fuel sock and hoping not to have to drop the tank to find out, I have a friend coming over with a fuel press tester tomorrow to see if I have to drop the tank.I am hoping it wont be that involve as I am in the process of building a new shop mainly insulating and trying to get everything together to install an outside wood burner.thank you for your input I only hope your not right.When I get this nailed I promise to let you know. Thanks again..murray
 
I think you maybe right about the regulator, thing is I have experience with the later model rs232 hookups but dont know anything about the paperclip method you mention.I would really appreciate any info you could give me on doing thatThank you...murray
 
Oh yeah Curtis,
you are right no check engine light ,just running for sh--
 
husky372 said:
I am familiar with the fuel sock and hoping not to have to drop the tank to find out, I have a friend coming over with a fuel press tester tomorrow to see if I have to drop the tank.I am hoping it wont be that involve as I am in the process of building a new shop mainly insulating and trying to get everything together to install an outside wood burner.thank you for your input I only hope your not right.When I get this nailed I promise to let you know. Thanks again..murray

If the 91 is like the 93-97s, you don't have to drop the tank to check the fuel sock. There should be an access panel under the rear carpet that will gain you access to the sock and fuel pump. Well I know the 93-97s are like this so I could be wrong.
 
Boy that would be great I guess i am to used to american made vehicles and just assumed i would have to drop the tank.
I would really like to thank everybody for the input on this.I cant tell you how much its appreciated.I will let you all know what I find so hopefully someone else can benefit.thanks again, murray
 
According to the FSM there is a service hole in the floor. Something you can do first is to perform the fuel pump operation step in the FSM.

1. Turn ignition on (don't start the engine)
2. Using a paperclip or wire , short the +B and FP terminals of the diagnostic connector (screwed to the firewall on the passenger side of the engine bay.)

You should hear fuel flowing through the return hose.( I would think you would be able to heare the fuel pump running also but the FSM doesn't say anything about that.)

If there is no flow, check the following parts:
Fusible links
Fuse (EFI 15A, IGN 7.5A)
EFI Main Relay
Fuel Pump
ECU
Wiring Connections

Disclaimer---This is straight from the Factory Service Manual. I am not experiences in troubleshooting fuel systems.

I had my EFI relay go bad in a circuit city parking lot 50 miles from my home 3 years ago. I drove back and forth from home 4 nights in a row before giving up and towing it to the stealership. $245 later ($12 in parts) they replaced the relay. Seams as if the ECU shut down the Ignition circuits when it foigured out there was no gas. I spent the whole time trying to get spark where there wasn't.
 
My 92 FJ80 would run poorly (hesitate, difficult to run over 2000 - 2500 rpms) after 2-3 hours of solid performance. After shutting it down for an hour or so the problem would disappear and then reappear. I replaced O2 sensors, wires, cap, rotor plugs, air filter and ran fuel cleaner. No luck. Mechanic replaced alternator due to low output. No help. I took vehicle to mechanic while problem was occuring and they found low fuel pressure. Replaced fuel pump. Problem solved. They were able to service fuel pump through hatch under carpet beneath second row seat. I hate intermittent problems!!!! Good luck and may the force be with you.

Rob
 
Fuel pump pre-filter (access panel under rear driver side seat-actually more to the middle) This should be done anyway and its 11 bucks and 20 minutes of work (mostly negotiating seats and carpeting). Go ahead and check the fuel pump operation per FSM...but this isn't going to tell you if your pre-filter is bad.

FPR sure, go ahead and check. Also valve clearances lately????

how do your plugs look-any odd smell/color/deposits?
 

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