94 80 series won’t accelerate until reaching operating temperature. (2 Viewers)

[Cruiser4Lyfe]

So I’ve been having an issue with my 94 the last month or so. When it started, I was on my way to work and after I pulled out of my neighborhood to get on the interstate, my cruiser seemed to just lose power as if I had taken my foot off the gas.

Sometimes RPMs would fall unless you put the accelerator to the floor, sometimes it would rev a little bit like the transmission wasn’t in gear. Weird thing is once it got fully up to temperature, it would run fine like nothing happened. Check engine light has never come on.

These issues were very consistent for about a month. Fast forward to last night, and i tightened the transmission cable just slightly hoping that might fix the problem. This morning when I fired it up, the thing wouldn’t idle and kept stalling. After the third try, it started and would drive but I couldn’t keep the RPMs above 1800-2000 and it wouldn’t go more than 25 mph. After running for a few minutes it snapped out of it and ran just fine 10 miles down the interstate at 75 mph.

The following troubleshooting/ maintenance items have been done in the last year:

1. Replaced O2 sensors.

2. Cleaned throttle body

2. Re-wrapped engine wiring harness next to EGR pipe a few weeks ago with electrical tape and high temp muffler tape and secured to the original mounting bracket with zip ties. No change. I can wiggle the harness near the pipe with the engine running and nothing happens.

3. Did a total trans fluid exchange by doing 5-6 drain and fills. Fluid is at correct level on dipstick when hot, and the fluid is a beautiful cherry red like it just came from the bottle.

4. Replaced the transmission filter and cleaned pan. Very little sludge on the magnets.

5. Sprayed brake cleaner on intake hose while idling. No change in idle.


From what I have read on here it could be a throttle position sensor, which will be here tomorrow, or transmission shift solenoids. Any thoughts?

I really appreciate all the help I’ve gotten here. Makes it possible for regular folks to keep rigs on the road that otherwise couldn’t.

 

[voodu3]

Check your accelerator cable. They get stretched over time. If it’s the original one it’s probably time for a replacement.

 

[Cruiser4Lyfe]

Check your accelerator cable. They get stretched over time. If it’s the original one it’s probably time for a replacement.

I did tighten it up a little last night; if anything the problem got worse.

 

[voodu3]

unhook the cable from the throttle body and see if it is moving freely inside the sleeve. It could be hanging up on on old grease or dirt that gets loosened up once the truck heats up.

 

[Cruiser4Lyfe]

So today it was to the point where I was doing 75 mph on cruise control, then the check engine light came (Codes 21, 26, 41) on and I lost all throttle response until I got down to about 25 mph. Had to limp back to the house on the shoulder of the road.

Ordered a spare TPS last week and put that on, so now the codes 41 and 26 are gone but code 21 remains.

Could this be something like a fuel pump or fuel filter causing the drive ability issues? I recall last year when my 02 sensors went bad It drove fine after it warmed up, it just wouldn’t run or idle when cold.

 

[REKCUT]

Did you look up the codes?? Might be a clue for you.

 

[Cruiser4Lyfe]

Did you look up the codes?? Might be a clue for you.

Yes, I looked up the codes. I am familiar with them. Code 41 is for the TPS sensor, code 21 and 26 were related to the O2 sensor. After my post last night I tried cleaning off the terminals in the 02 connectors and sealing with dielectric grease and the check engine lights disappeared, but the symptom of randomly stalling remains.

 

[JeepinPete]

Try running with the O2 sensors unplugged. Won't hurt anything, and will determine if they or their wiring is the issue. My '93 was having driveability issues, which turned out to be the O2 sensors. I've been running with them unplugged for the last month...

 

[BILT4ME]

Have you considered checking your temperature sensors?

It appears that the issue is occurring when the engine is in open-loop operating condition and goes away when achieving closed-loop which is temperature related.

The open loop / closed loop also affects the voltage to the fuel pump to change fuel pump speed from open to closed.

 

[Cruiser4Lyfe]

Have you considered checking your temperature sensors?

It appears that the issue is occurring when the engine is in open-loop operating condition and goes away when achieving closed-loop which is temperature related.

The open loop / closed loop also affects the voltage to the fuel pump to change fuel pump speed from open to closed.

I haven’t..... but it sounds like that could be a promising lead. I do have a valve cover gasket leak that I’m about to address, so perhaps some oil has gotten into the connector and impeded connectivity. My dash coolant temp gauge has never fluctuated at all though... would it show on the gauge if it was having problems or not necessarily ?

 

[BILT4ME]

I haven’t..... but it sounds like that could be a promising lead. I do have a valve cover gasket leak that I’m about to address, so perhaps some oil has gotten into the connector and impeded connectivity. My dash coolant temp gauge has never fluctuated at all though... would it show on the gauge if it was having problems or not necessarily ?

There are two sensors. one for the gauge, one for the ECU.

I assume 95+ on year?

 

[polloelastico]

AFAIK the ECT sensor (Part# 89422-35010) is different from the sensor that feeds the gauge on your dash. I just changed mine (it's the on the block, below the intake manifold, third one back) and the plastic connector on it basically crumbled in the deep 19mm socket when I removed it. The brass sensor bad was also in terrible shape, super corroded. Make sure you get the little copper washer/gasket (Part# 90430-12005) as it does not come with the sensor. You can do this in 10 minutes, i just reached in from the top and under; visibility is poor so a lot is by feel, but it's doable for sure.

 

[Cruiser4Lyfe]

There are two sensors. one for the gauge, one for the ECU.

I assume 95+ on year?

Mine is a 1994 with a 12/1993 build date.

Thanks

 

[BILT4ME]

Mine is a 1994 with a 12/1993 build date.

Thanks

OBD1 has a bit of a different operational sequence. Have you followed the troubleshooting in the FSM?

 

[Cruiser4Lyfe]

OBD1 has a bit of a different operational sequence. Have you followed the troubleshooting in the FSM?

I haven’t bought the FSM so far since anything I’ve needed to do I’ve been able to look up on here. This is probably the time that needs to change...

 

[BILT4ME]

Post 496. Google Drive Link

For Sale - 40, 50, 60, and 80 series FSM for a hell of a price.

It's an end of an era my friends. As of tomorrow I'm being forced by my isp provider to shut this down. I just cannot take the chance on losing my hosting for my e-mail and other things. I'm working on finding a new home for the files as I believe they are a valuable resource. 8 years I've...

forum.ih8mud.com

 

[flintknapper]

AFAIK the ECT sensor (Part# 89422-35010) is different from the sensor that feeds the gauge on your dash. I just changed mine (it's the on the block, below the intake manifold, third one back) and the plastic connector on it basically crumbled in the deep 19mm socket when I removed it. The brass sensor bad was also in terrible shape, super corroded. Make sure you get the little copper washer/gasket (Part# 90430-12005) as it does not come with the sensor. You can do this in 10 minutes, i just reached in from the top and under; visibility is poor so a lot is by feel, but it's doable for sure.

 

[Cruiser4Lyfe]

Post 496. Google Drive Link

For Sale - 40, 50, 60, and 80 series FSM for a hell of a price.

It's an end of an era my friends. As of tomorrow I'm being forced by my isp provider to shut this down. I just cannot take the chance on losing my hosting for my e-mail and other things. I'm working on finding a new home for the files as I believe they are a valuable resource. 8 years I've...

forum.ih8mud.com

Incredible. Thanks for pointing me in that direction.... definitely beats paying 200 bucks for a used printed copy.

 

[Cruiser4Lyfe]

Just wanted to post an update here. Finally got back out on the road after a front diff/ front axle rebuild. I also replaced the ECT sensor with a brand new one, and there’s no change in behavior. I was just driving on some country roads at 55-60 mph and the thing almost left me on the side of the road until the coolant temp reached a little over 160 degrees according to my temperature probe I have on the thermostat housing. the engine would rev but it’s like the transmission was in neutral.

After the temp got past about 165 it ran beautifully like it should, with no problems.

Next step is to unplug the O2 sensors to see if anything changes. I’ll report back.

 

[Cruiser4Lyfe]

Well... I unplugged the O2 sensors and no change.