RPMs drop when accelerating (1 Viewer)

Joined
Aug 12, 2018
Messages
6
Location
Phoenix, AZ
I have a '94 80-Series that hesitates when getting on the accelerator. It's been intermittent for the past few months but now is more the rule than the exception. If I press the gas slow and smooth its normal but when I accelerate as I would typically it hesitates and drops RPM to the point where it feels like its about to stall. The timing and TPS were recently dialed in (by a pro) but its still occurring. Any suggestions are welcome.

Truck has 140K miles

Thanks in advance!

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Joined
Mar 14, 2020
Messages
147
Location
california
I have a '94 80-Series that hesitates when getting on the accelerator. It's been intermittent for the past few months but now is more the rule than the exception. If I press the gas slow and smooth its normal but when I accelerate as I would typically it hesitates and drops RPM to the point where it feels like its about to stall. The timing and TPS were recently dialed in (by a pro) but its still occurring. Any suggestions are welcome.

Truck has 140K miles

Thanks in advance!

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Was it like this before the timing and the TPS calibrated?
Does the RPM fluctuate at idle or at a stop light?
Could be various of things but 1st I would check is the fuel filter-could be clogged.
 
Joined
Apr 5, 2006
Messages
799
Location
Canyon Lake, TX
First thing that comes to my mind is the fuel pump relay. If there is a bad spot on the contact, and it is switching from low voltage to high voltage when you hit the accelerator, it may be monmentariliy interupting the power to the fuel pump. Not hard to pull it and visually check it.
 
Joined
Aug 12, 2018
Messages
6
Location
Phoenix, AZ
First thing that comes to my mind is the fuel pump relay. If there is a bad spot on the contact, and it is switching from low voltage to high voltage when you hit the accelerator, it may be monmentariliy interupting the power to the fuel pum

Thanks! I will take a look at the relay and then dive into filter, etc. and report back on progress.

The idle does fluctuate a bit at a stand still but its not all over the place - its as if the ECU is not happy and trying compensate. This was occurring off and on prior to the TPS being calibrated.

As for the oil pressure: The gauge does always read great oil pressure (I just assume and hope the gauge is correct)
 
Joined
Aug 12, 2018
Messages
6
Location
Phoenix, AZ
I had been chasing this for months! O2 sensors, TPS, timing, IAC, ignitor, MAF, fuel pump relay, trial, error, cleaning, replacing, testing and/or buying.........
The culprit? It was the Engine Coolant Temp Sensor. $45 bucks (OEM), 30 minutes and voila!

Thanks to this forum for the help!
 
Joined
Aug 12, 2018
Messages
6
Location
Phoenix, AZ
How did you diagnose it (?Trouble Code 22)?
There was no associated CEL so I didn't have any codes to pull. It was diagnosed through trial and error and a lot of frustration. As it progressed it became apparent that on cold start the primary symptom was a very high idle. The RPM stutter would then begin to occur after a warm start or just as the engine got up to temp. The past few weeks the engine was running so rich at temp that it was flooding (I think) and would not start again until it cooled down. That's when I started looking into temperature related items.
 

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