Random misfire, bad idle, terrible acceleration

[msrebecky]

Well I cleaned the contact points inside the cap and sprayed the oil out of and off of everything with electrical contact cleaner. Also dried it out very thoroughly with a hair dryer. Put everything back together and same issue. Driveable but still an irregular misfire/thump/stutter. Does not seem to happen when revving in nuetral unless I stab the throttle. Can coast in nuetral or drive with no problem and even maintain steady speed on flat ground. Come an incline or need to accelerate and it's there again.

So for now I guess I need to replace the cap, rotor and plug wires. Also need to check and isolate the wiring harness. Just haven't had time to dig to deep into that yet.

At this point I have done the following:
-Replaced the ignition coil
-Changed the spark plugs (all gapped to .031")
-rechecked the plugs (all look good, slightly white on top of electrode but clean inside the gap)
-Pulled apart and soldered back the MAF/VAF
-changed the o2 sensors
-checked the intake hose (no cracks)
-checked all the fuses and relays that I can think of (all good)
-cleaned the distributor internals

Am I missing anything? I'm thinking if the dizzy cap, rotor, and plug wires don't fix this I'm gonna have to go to a mechanic. At a certain point I'm not saving money any more and have a tendancy to get in over my head.

 

[fz1boxer]

have you been able to check timing?
look underneath and see if knock sensor is intact/plugged in.

 

[msrebecky]

I need to put on the new knock sensor connector. Was broken off at the plug. Could that be a problem? Seemed to me like it would only be a problem if there was a knock.

 

[fz1boxer]

yes

 

[Rics4rnr]

Did the connector pin break off on the knock sensor? I had to remove my old knock sensor with a 27mm socket and I purchased a new sensor wire 82219-35010 if the connector is bad.

 

[ZackR]

I didn't see checking the wiring harness by the EGR on your list.... report back once you dig into that part.

 

[BILT4ME]

The knock sensor will adjust the timing while in operation and could likely be that cause of the issue.

Fix the knock sensor wiring first.

Otherwise, the fact that it is only misfiring under load indicates it could be a fuel or timing problem.

Things that affect fuel delivery would be next on the list.
IAC Valve (Idle Air Control Valve)
VSV (Vacuum Switching Valve) (affects fuel pressure)
Fuel Filter
Temp Sensor (Once the engine reached operating temp, it drive it into closed loop and changes the fuel pump speed) There are two. One for the ECM and one for the gauge.
Filter sock on fuel pump
Fuel pump

 

[msrebecky]

Did the connector pin break off on the knock sensor? I had to remove my old knock sensor with a 27mm socket and I purchased a new sensor wire 82219-35010 if the connector is bad.

the wire was broke off right at the connector. Bought 2 new connectors to replace both just in case.

I didn't see checking the wiring harness by the EGR on your list.... report back once you dig into that part.

I trying to knock out what seems like some more simple tasks before I get there. Seems like i may be in over my head with something like that I don't want to end making the problem worse.

The knock sensor will adjust the timing while in operation and could likely be that cause of the issue.

Fix the knock sensor wiring first.

Otherwise, the fact that it is only misfiring under load indicates it could be a fuel or timing problem.

Things that affect fuel delivery would be next on the list.
IAC Valve (Idle Air Control Valve)
VSV (Vacuum Switching Valve) (affects fuel pressure)
Fuel Filter
Temp Sensor (Once the engine reached operating temp, it drive it into closed loop and changes the fuel pump speed) There are two. One for the ECM and one for the gauge.
Filter sock on fuel pump
Fuel pump

It misfires while in idle but not nearly as bad when under load.
I'll look into the things that you mentioned. Seems like it's getting plenty of fuel though.

Thanks for the help guys. Definately appreciate the straight answers.

 

[Rics4rnr]

Hello. I have a 1994 Land Cruiser that I recently bought. Close to 300k on 5he odometer and has been running fine until last week. Started to idle rough and accelerate poorly. Been going through the different threads to pinpoint the issue. What really has me stumped is while changing the spark plugs, i noticed a connector to the driver side of the back plug (under the egr modulator I believe) was unplugged and looped back into its self on the female side. Also the EGR modulator tubes connecting to the throttle body were disconnected and looped back as well. Both sides. The throttle body side and modulator side. Is there any particular reason for this? Could it be my problem for the idle and acceleration? Don't want to plug them back in and cause a bigger problem. I'll try to get pictures after work.
Thanks.

I purchased my 97 80 this past spring and I had a rough idle and struggled to accelerate. I ended checking all the vacuum hoses and heater hoses because they are know to dry rot through the years. I replaced the vacuum hose one at a time and checked for cracking in the vacuum hoses. I just done the throttle body and upper intake plenum that also helped with the acceleration because if your 80 never had the plenum cleaned out I am sure that there is carbon build up on ERG port to the throttle body.

 

[ZackR]

I trying to knock out what seems like some more simple tasks before I get there. Seems like i may be in over my head with something like that I don't want to end making the problem worse.

Its actually not too tough to tackle. I used a pair of wire cutters to carefully open up the wiring loom and peel back the foil to see what condition the wires were in. I went through the same steps as you and did a full tune up, new plug wires, etc... to no avail, until I sorted out the wires by the EGR.

 

[msrebecky]

I purchased my 97 80 this past spring and I had a rough idle and struggled to accelerate. I ended checking all the vacuum hoses and heater hoses because they are know to dry rot through the years. I replaced the vacuum hose one at a time and checked for cracking in the vacuum hoses. I just done the throttle body and upper intake plenum that also helped with the acceleration because if your 80 never had the plenum cleaned out I am sure that there is carbon build up on ERG port to the throttle body.

Vacuum hoses all look new except for the ones at the charcoal canister. Could this be part of the issue? Sounded like a hissing came from it when I release the throttle cable at the throttle body.

 

[Rics4rnr]

Vacuum hoses all look new except for the ones at the charcoal canister. Could this be part of the issue? Sounded like a hissing came from it when I release the throttle cable at the throttle body.

When in doubt swap it out. Also I noticed you have the old heater hoses with pins. if you ever plan on replacing the hoses I made a kit for all the hoses that i just completed on my 80.

 

[MyCrush]

Those symptoms look familiar to me from just a couple years ago. I replaced what you have W/ no progress. Replaced VAF...been good ever since.
I see you fixed the VAF....have you checked your work against FSM VAF testing specs?

 

[msrebecky]

When in doubt swap it out. Also I noticed you have the old heater hoses with pins. if you ever plan on replacing the hoses I made a kit for all the hoses that i just completed on my 80.

I plan on doing so. I'll hit you up when I do.

Those symptoms look familiar to me from just a couple years ago. I replaced what you have W/ no progress. Replaced VAF...been good ever since.
I see you fixed the VAF....have you checked your work against FSM VAF testing specs?

No. Not a clue how to do that. If it involves a volt meter it's a different language to me. I wouldn't be surprised I put too much solder on the connections though.

 

[MyCrush]

I replaced w/ used as the VAF has been NLA for some time now. Never even put a meter on it....just replaced it after going thru most everything else...I’ve been GTG since.
That said, here it is, in it’s very simplistic format.
You’d be testing for ohm range..a meter with have that upside down ‘U’ symbol as a selection to make. It’s also not explained literally, but you are to move the inner flap/door with your fingers as you observe the ohm range readings from the leads on the corresponding input points.

Also, if you’ve opened the silicone sealed shut, flat black cover on the top to look at the innards....It’s the widespread consensus here that there is nothing inside to fool with, so don’t open.

 

[msrebecky]

Also, if you’ve opened the silicone sealed shut, flat black cover on the top to look at the innards....It’s the widespread consensus here that there is nothing inside to fool with, so don’t open.

Yep. Definitely did it. Had to. Pulled to hard like an idiot. Guess Ill check this now. Thanks for the info. I really need to get an FSM.

 

[MyCrush]

Picked up my replacement from @Deathvalleypaul
Might be worth a shot to see what’s available from him. IMO

 

[BILT4ME]

There is now an "unproven" reman unit available from RockAuto.

 

[msrebecky]

Drove it around for a while. Seemed like it took longer than usual for the symptoms to arise after a cold start.

VAF tested and within tolerances.

Knock sensor connector replaced.

 

[msrebecky]

Scratch that. Just let it cool for a while and went to start it again. Started stumbling shortly after startup. Also noticed that there is an excessive amount of moister/ steam from the exhaust. More that usual on a cold day. Could it possibly be a tank of bad fuel?