2.9L engine stalls

[dend]

Hi. I am new to this forum, and would appreciate your advice. I inherited a 1987 Ranger with 2.9L with auto transmission. It starts and idles well at cold startup. After short warmup when you try to give it throttle the engine will start to die out then have erratic acceleration and dying out. After full warmup it does the same thing when driving. It does seem to accelerate properly if you accelerate hard. It was worse before I tuned it up, and would not idle after a minute or two. After testing and replacing the MAP the truck idles well. I replaced plugs, wires, cap and rotor button, MAP, and fuel filter. I tested the TPS with a voltmeter and voltage increase was smooth with no flat spots. I put a can of sea foam through the throttle body, and sea foam in the fuel. I Disconnected the IAC to see if that would have an impact, and the truck would not start. Not sure if that means the IAC is “working”. Any help would be appreciated.

 

[RonD]

Welcome to TRS

Reads like you have done all the right things

Fuel injected gasoline engines still need to be Choked when cold, but without Jets a choke plate won't work
So the fuel injection computer(PCM) has a coolant temp sensor(ECT) that it uses so it knows when and how much Choke to apply to the cold engine, and when to remove the Choke
It should be on the lower intake by the thermostat housing
There will be TWO similar "looking" units
One is for the dash temp gauge, has 1 wire and uses 12volts, a Sender
The other has TWO wires and uses 5volts, thats the ECT sensor
5v in and 3volts out is cold
Under 1volt out is warmed up
Many just replace these because they are not to expensive

And then there is the O2 sensor, computer doesn't use these until engine is warmed up, an O2 sensor needs to be above 650degF to work
O2 sensors use a chemical reaction to generate voltage when Oxygen is present in exhaust, and they simply run out of chemicals after 150k miles or so or 10 years, so do need to be replaced, unlike other sensors
And a worn out O2 can cause poor engine running after warm up
Computer also Ignores O2 sensors when accelerating hard, so when TPS voltage goes up fast, computer reverts to tables in memory for adding fuel faster for best power, it assumes MPG is not the concern for the driver at that time, lol

 

[rusty ol ranger]

Coolant sensor. Bout guranteee

 

[dend]

I’ll give those a try and let you know what happens. Much appreciated!

 

[dend]

Had some time to revisit the ranger today. I thought I would do some additional tshooting after learning from Ron about the way it’s supposed to work (thanks for the education). I started the truck and attempted to drive it while cold. It hesitated badly, would stall and then the engine would repeatedly surge and stall. Again it would go if accelerating hard. I parked it and it cut off. The engine was still cold at this point. I restarted it and it would idle as long as I didn’t touch the throttle otherwise it would surge and stall repeatedly. I did notice while idling that the engine seems to have a miss and slight drop in RPMs and then will pick back up again. It will stay running and idle like that as long as I don’t touch the throttle. I let it run until warm and it behaved the same. I was going to buy the temp sensor, but thought I would test it cold to see how it behaved while cold. I expected it to run properly (or at least differently) while cold, but it didn’t. Should I still replace the temp and O2 sensors or does it sound like something else? Thank you.

 

[PetroleumJunkie412]

Have you checked base timing?

 

[franklin2]

Yes, pull the spout connector while it's idling and see what it does. If it kills it that is a big hint the timing may be off. If the timing was set without pulling the spout, that could be your problem.

 

[RonD]

+1 ^^^

 

[dend]

I pulled the spout connector (after I researched what it is and where to find it) while idling after the engine was warm. The rpms dropped some , but continued to run. I have a timing light from years ago, but don’t have a tach so I could not check the timing. I appreciate the help and the education.

 

[PetroleumJunkie412]

Wait.

Whats a tach have to do with it?

A tach has absolutely nothing to do with checking timing.

Thats like saying you need a pickle to perform open heart surgery.

Your truck sounds out of time.

Pull the spout connector. Clip timing light to plug wire #1. Aim the timing light at the needle, not the loop. Report back.

 

[dend]

Ok. I read an article that said I had to set the timing at a specific RPM, and that’s what I thought I was supposed to do. Good thing I’m not a mechanic by trade. Thanks for the help.

 

[dend]

Spent a few minutes with the Ranger this evening. Just for grins I checked the timing on startup with the spout connector in place. It was hard to see, but I think it was 37 then it dropped to around 22. I waited until the engine was warm and pulled the connector. It was clear to see and the timing was exactly 12. I know it’s supposed to be 10, but I’m not sure if that is significant on this vehicle. Thoughts on what that means and what I do next? Thanks for the help guys!

 

[PetroleumJunkie412]

12 means that someone bumped timing for a little more power.

Ron?

 

[franklin2]

12 should be fine. Glad you got that checked and that can be eliminated as the problem.

 

[dend]

So does that mean I am back to replacing the Coolant Temp Sensor? I have read Ron’s explanation about how that sensor works a few times to better understand how the pieces fit together, but I’m puzzled by why the truck accelerates properly hot or cold under heavy throttle. I have never worked with fuel injection, but with older vehicles in a limited amount and when they are choked they stammer under throttle. Thanks for the information. I’m learning a lot.