2.9 won’t rev over 3000 rpm

[Ranger 1988]

88 2.9 4x4 auto
At around 3000 rpm under no load (trans in park) develops severe miss. Tach drops and bounces at same time. Idles fairly smooth at 850. The missing or sputtering also occurs while driving. Problem started abruptly while driving a few weeks ago. Check engine light came on and code was weak ign pick up signal. After replacing dist no codes are seen with koeo and koer.

I’ve seen these 2 symptoms on several old threads with no resolution posted so thought I would post new thread.

Installed new distributor assy, plugs, wires, tps, iac and tried another used ecm and manifold vac sensor.
No improvement.
Also installed new fuel tank, both fuel pumps, filter, and fpr. Installed fuel pressure gage so I know pressure is steady at 32 psi while engine misses at 3000 rpm.
Any help is appreciated.

 

[franklin2]

I wonder if the catalytic convertor is clogged? The previous miss-fire could have overheated it and now it's clogged or broke loose inside? Just a guess.

 

[SenorNoob]

If fuel pressure is stable, how about vacuum? Or ignition?

 

[Ranger 1988]

Planning to remove cat and check for blockage in next few days. I’ll also check vacuum. Ignition seems to be dropping out momentarily based on the way the tach drops when rpm approaches 3000.

Today I found 4wd not working since the ecm I installed came from 2WD truck. Since this ecm didn’t solve the problem I reinstalled the original ecm. When I started truck it appears this ecm has now completely failed. Will have new one tomorrow. I hoping this is the problem and the spare ecm I tried is failing too.

 

[Ranger 1988]

New ecm did not solve problem. Still starts running rough between 2500 and 3000 rpm. Will not go beyond 3000 rpm.

 

[SenorNoob]

88 PCM doesn't control the transfer case. It has a separate control module. I have one sitting in my parts right now.

 

[Cees Klumper]

Since this started abruptly as you write, I would look for ignition or fuel supply related causes. Too bad there's no codes. I would swap out the TFI module and test the coil and spark plug wires for starters, clean and check the various ground connectors (ECU, engine etc) and also check the spout connector is seated well, and check all vacuum lines.

 

[Ranger 1988]

88 PCM doesn't control the transfer case. It has a separate control module. I have one sitting in my parts right now.


Thanks, good to know this. 4wd was probably working but the indicator light is weak at times. I didn’t drive it. The other reason I wanted to reinstall the original ecm is the used spare I have came from a manual trans truck and mine is auto.

 

[Ranger 1988]

Since this started abruptly as you write, I would look for ignition or fuel supply related causes. Too bad there's no codes. I would swap out the TFI module and test the coil and spark plug wires for starters, clean and check the various ground connectors (ECU, engine etc) and also check the spout connector is seated well, and check all vacuum lines.

Tfi is new but it could be bad. I drove yesterday up to 45 mph briefly and problem gets worse as engine warms up. I’m thinking that if cat was not clogged before it might be now with all the miss fires.

Also it has small exhaust manifold leak. Could this allow oxygen in and affect o2 sensor operation?

 

[rusty ol ranger]

Tfi is new but it could be bad. I drove yesterday up to 45 mph briefly and problem gets worse as engine warms up. I’m thinking that if cat was not clogged before it might be now with all the miss fires.

Also it has small exhaust manifold leak. Could this allow oxygen in and affect o2 sensor operation?

Yes it *could* but not likely causing your issue.

Its cat or ignition.

 

[TheTinMan]

88 2.9 4x4 auto
At around 3000 rpm under no load (trans in park) develops severe miss. Tach drops and bounces at same time. Idles fairly smooth at 850. The missing or sputtering also occurs while driving. Problem started abruptly while driving a few weeks ago. Check engine light came on and code was weak ign pick up signal. After replacing dist no codes are seen with koeo and koer.

I’ve seen these 2 symptoms on several old threads with no resolution posted so thought I would post new thread.

Installed new distributor assy, plugs, wires, tps, iac and tried another used ecm and manifold vac sensor.
No improvement.
Also installed new fuel tank, both fuel pumps, filter, and fpr. Installed fuel pressure gage so I know pressure is steady at 32 psi while engine misses at 3000 rpm.
Any help is appreciated.

Have you checked your coil? I've had that same issue before and it drove me crazy then I connected an oscilloscope to the coil and found that it dropped out at higher revs

 

[Ranger 1988]

Have you checked your coil? I've had that same issue before and it drove me crazy then I connected an oscilloscope to the coil and found that it dropped out at higher revs

I tested a used coil and it ran the same but it could be failing too. I can’t check with an oscilloscope so I might try a new coil since it is the only part in the ignition system that has not been replaced with a new part.

 

[Ranger 1988]

Installed new coil with no change to problem. Still begins to miss between 2500 and 3000. Now entire ignition system is new. Also removed cat and was surprised that I didn’t see any damage with all the misfiring. Gutted the cat anyway and reinstalled.

 

[franklin2]

Just checking. When you replaced the distributor you set the timing with a light to 10BTDC with the SPOUT connector unplugged?

 

[Ranger 1988]

Just checking. When you replaced the distributor you set the timing with a light to 10BTDC with the SPOUT connector unplugged?

yes, set timing just as you described