Intermittent power loss, when cold out at altitude? (1 Viewer)

[b16]

Hello Mud,
I've had this happen 2x now, yesterday being the most recent.

When I was driving back from Tahoe about 2 months ago during a snow storm at ~6,000 ft. The truck would suddenly lose power, like I lifted off the accelerator. I had resistance in the pedal, but not translating to actual engine output, instead it decelerated.

What is strange is it seemed to operate ok below 2,500 rpm. Then I also found if I put the pedal to the floor for the kick down, it would then get power back.

I thought it was my old cracked intake arm that was the problem. I replaced that and didn't get any symptoms. Even did a few more trips to the snow with no issue.

Now last night on the way back home it did it again. What is strange is when I got back down to about Auburn CA the issue never came back.

Definitely feels like an issue with the engine, engine would stumble and almost feel like it was going to die, floor it and it would sputter back to life and eventually go at full throttle.

Any ideas?

 

[Landseer]

Several possible causes are bad MAF, throttle position sensor, fuel pump relay, fuel pump itself, EGR activating when it shouldn't, among others. If you cant reliably recreate the problem (which seems likely if its only happened twice) it will be hard to narrow down what the root cause it. You might want to start by getting an OBD2 reader so you can see what the various sensors are reading in real time.

 

[b16]

I do have a wireless OBD2 scanner and a free app. Good point, don't know why I didn't think of that when it was occurring. It does "feel" like a bad MAF or TPS which is why I thought it was that intake arm before. Like it is not metering air properly at times. Never heard of a MAF going bad though, do they?

 

[Landseer]

MAFs will occasionally go bad although its not really a common failure on 80s.

 

[tylerbre]

@b16 did you ever solve this issue with your 80?

Having almost exact same issues, and even went through the trouble of replacing the MAF with a better functioning one and still the issues persist...

 

[b16]

@b16 did you ever solve this issue with your 80?

Having almost exact same issues, and even went through the trouble of replacing the MAF with a better functioning one and still the issues persist...

I have not had it occur since I replaced the intake tube, plugs, wires and dist cap. Not really sure which of this may have been the real culprit.

 

[PeterTheBeater]

I have not had it occur since I replaced the intake tube, plugs, wires and dist cap. Not really sure which of this may have been the real culprit.

I have a similar issue now but I had a tuneup 20k miles ago.

 

[tylerbre]

Just to tack onto this thread, my issue was not actually intermittent power loss, but a 2200 rpm rev limiter being applied... This felt like power loss because the car would stumble past around 30mph. There are tons of threads on here about the 2200 rpm rev limiter, which if I had searched originally would've have allowed me to solve this much earlier on...

Anyways it was solved by adjusting the TPS. I think it may have been caused by not adjusting a replacement throttle cable. It only happened when the truck was fully warmed up.

So to anyone who is experiencing this, try to pull it over, pop the hood and try to manually rev out the engine from the throttle body. If you experience essentially a fuel cut rev limiter at 2200 rpm, try adjusting the TPS in slight counterclockwise increments until you can fully rev out the engine. Then shut the truck off, disconnect the battery for a minute, reconnect and you should be good.

In my case I didn't find it all that helpful to do TPS adjustment as the FSM states, I have a '94 so no OBD2 and while I did use my multimeter, I still didn't get it quite right.

 

[PeterTheBeater]

I have a similar issue now but I had a tuneup 20k miles ago.

Replacing my O2 sensors solved my issue. One of my O2 sensors was out of range on its resistance.

 

[greentruck]

I have not had it occur since I replaced the intake tube...

That may very well be a major contributing factor if it was leaking. They get old, stiff, and develop cracks that are hard to see, but which will leak nonetheless. The MAF sees things one way, because it's on the end of the tube that gets a good airflow measurement, but past that the leaks add in air that's unaccounted for by the computer. Ours was held together with duct tape for a long time. The price was reasonable and R&Ring it resulted in a notable and obvious performance improvement. The new tube also improved the junkyard looks of our engine bay by getting most of the duck tape out.