Okay, so I am completely puzzled and hope one of y'all can help.


Short Version

After a coolant flush/new plugs, my 1991 ranger with the 2.3 no longer has any power and won't break 40mph.


Background

I've got a 1991 ranger with the 2.3 that I got running in 2015 and have been driving since. However I installed the thermostat incorrectly from the get-go, but made the dumb mistake of assuming the engine not heating was a symptom of a failed temp sensor. Therefore, for about 30,000 miles, the truck never, truly, got warmed up. Despite this, it ran really well. A few week ago, it started leaking coolant, so I replaced the pump and thermostat. The coolant was really, really gross, so I also ran a bottle of the Preston Max coolant flush through the system for 3h and drained it immediately after. While I was in there, I also noticed the plugs were in bad shape and that the wires had started to fall apart. I went ahead and replaced those as well with NGT plugs and wires. Note that I removed the upper intake manifold and throttle body to access the plugs behind them.


The Problem

At idle, the truck runs okay, if a little rough. The intake vacuum bounces between 10 and 20 inHg pretty quickly before settling to around 12-13. If I give it some gas up to around 3000 RPM, the engine looses power and the RPM drops to around 2000 RPM (see gif below). The engine just bounces between this high and low RPM as long as it's given gas. When I release the gas and the RPM drops, the vacuum bounces wildly between about 5 and 25 inHg before settling back to the normal idle state.

Out on the road, the tuck has no power. It seems to be tied to pressing the accelerator more than the RPM, but that is somewhat difficult to separate. I will give it gas to try to accelerate, it will stumble for a few seconds and I'll let of a bit, and it "catches" at some point and I can feel the power come back and the truck will start accelerating.

There is a bit of exhaust leaking from somewhere near the engineer. Also, there is quite a bit of white smoke when I start the truck from cold, but this soon goes away.


Theories

1. Getting the truck hot after having been run cold for so long broke free a lot of crud in the engine. This is causing issues with the valves or catalytic converter.
2. I reassembled something incorrectly, and just haven't found the problem yet.

Attempted Fixes

1. Verified the order of the spark plug wires.
2. Checked for vacuum leaks.
3. Unplugged MAF to run truck in open-loop to isolate if it's an emissions issue. It behaved the same.
4. Checked and rechecked and triple checked for coolant in oil or dropping coolant level.
5. Tested the throttle position sensor and EGR valve.
6. Ran fuel system cleaner and a bottle of Sea Foam top engine cleaner through it.
7. Looked for anything that had been left disconnected.
8. Checked compression, and all cylinders read 180psi.
9. Checked fuel system, and had 40psi at rail under idle and 2500RPM.
10. Checked plugs after about an hour of cumulative run time. Plug on cylinder three was clean while the rest had quite a bit of carbon (see image).
11. Peaked under the valve cover, but didn't see any obvious damage. The springs were obscured a little, though, so I may have missed something.
12. Checked resistance and spark in primary (RH) coil. All seemed to be working okay.

I am at a loss. Any help would be greatly appreciated.


RPM bouncing under constant gas.



Plugs after about an hour of use

 

Welcome to the forum

Definitely running Too Rich as spark plugs show, or burning oil via intake valve seals

The 180psi compression and the 12" of vacuum don't fit together unless exhaust is blocked
You can pull out the O2 sensor and start engine, gives exhaust an exit, it will be LOUD, lol, and see if things smooth out, steadier and higher vacuum
(O2 sensors only last 12 years or 100k miles, so may want to put back in a new one, old O2 will cause Rich running, poor MPG)

When was the timing belt and tensioner last changed?
Older belt and tensioner can give good compression at cranking RPM but erratic cam/piston timing at running RPM

 

Thanks for the tips! Unfortunately, we have gone from bad to worse as I'll explain below.

• I took out the O2 sensor and fired up the truck. It behaved the exact same (except for the new fun "popping" sound).
• Next, I pulled the spark plug wires from the passenger side to test the other coil. I didn't realize that only that coil was used when starting, so when I tried to start the truck it just turned over.
• So I hook everything back up and decide to remove the air filter cover and try it without any obstruction. Unfortunately, the truck no longer would start. It sputters a bit and then dies.

The thing I keep wondering is why now? The problem had to be triggered by the coolant flush, the new plugs/wires, or the engine getting up to temp for the first time in years.
My current plan is to

1. Swap out the new plugs with motorcraft plugs and the original wires. Maybe the new plugs are doing something squirrelly.
2. If that doesn't help, I'll look into replace the timing belt and tensioner.

I'm still very confused what is going wrong, so please share any other ideas you have.

 

The truck started up again this morning. I'm guessing that turning it over without spark just dumps too much fuel in the cylinders. It's no better, but at least it's not worse either.

 

I tried new plugs - no change.
I tried plugging the PCV - no change.
I verified that I have spark through a range of throttle positions (I won't say RPMs because those two things are pretty decoupled in the truck currently).

Am I right in assuming that poor performance at WOT implies that the problem is not a vacuum leak?

I am running out of cheap things to check. The next two things on my list are

1. Check the engine timing to ensure it's not jumping around.
2. Check for worn wires/bad grounds on as many of the sensors I can get to.

 

Bad sensor or sensor wiring would set a code

Vacuum leak causes issues at any throttle position even WOT, but O2 sensor is ignored at WOT
O2s main function is best fuel economy, and computer assumes POWER is the only concern at WOT

Unplug MAF sensor
Start engine
See of CEL(check engine light) comes on, it should, this is a sanity check for computer
Also see if engine runs any better with no MAF sensor, no MAF holds computer in Open Loop mode

 

I had unplugged the MAF sensor and nothing changed. The CEL comes on when it's unplugged, so that's working. I've never been able to pull any codes though. The truck had sat for a number of years, and a rat got to some of the diagnostic wiring. I will try again though. It would be nice to get some more clues.

 

I had to take a break over the holidays, but I took another look yesterday and eliminated a few more things.

1. I managed to get the code reader working. After squashing a few easy codes (e.g. idle screw was set too high), I managed to get the all clear for both the key-on-engine-off and engine-on test.
2. I completely disconnected the exhaust just to verify there wasn't a restriction. The truck still behaved the same.
3. I checked the timing with a timing light after unplugging the inline spout connector. It was pegged at the factory 10° and it would still almost die if I opened the throttle.
4. I sprayed carb cleaner around the intake manifold looking for leaks but didn't notice a change in the RPMs.

The only thing I noticed different is the truck finally stopped blowing so much white smoke. Maybe now that I have been running it for longer periods I dried out the exhaust system. Before it stopped, it was dripping some pretty sooty water from the tail pipe, but this didn't seem too surprising giving the state of the plugs.

I'm back to thinking that maybe it is something going on with the fuel system.

 

A hesitation with SPOUT unplug is normal
But do this
engine warmed up
See what the timing is, should be 20-22deg BTDC
Unplug SPOUT
Should drop to 10deg BTDC

The SPOUT is the same as the "Vacuum Advance" used on older distributors, its just an electronic version from the computer
Computer has the Engine Load info, so like intake Vacuum level on older models, but better than vacuum advance
If SPOUT is not working then Driving would be poor

 

It was around 20-25 with SPOUT enabled. My point was that either way (enabled or disabled) the truck still had the same problem. This suggests to me that timing probably isn’t the problem.

 

Ignition timing isn't the problem, but maybe valve timing is? I read that you can jump teeth by turning the engine back the wrong way. I may have done this when I was attaching the fan to the water pump, I can't remember. I checked the timing by turning the engine (the right way) until the triangle cast into the camshaft sprocket aligned with the timing mark on the back cover (see first image). At this position, the crankshaft is about 40ª BTDC (see second image). This seems like a lot, so I am afraid I am missing something. ​​​​​​Am I checking the timing correctly?


View of camshaft timing marks


Notch location in crankshaft pulley when camshaft is aligned as in other image.

 

Digging in a little further, I confirmed that the timing had jumped 3 teeth. I'm honestly surprised that it was running as well as it was.

I've got a new belt coming. Is there anything special that I should know before putting it on? Also, the oil pump pulley only has the cast alignment mark that the camshaft pulley has (there are no triangles/diamonds to align). I saw elsewhere that this year (1991) did not have a specific alignment for the oil pump, so the timing mark should just be set pointing straight up. Is this correct?

 

Correct about the AUX(oil pump) gear, it only needs to be aligned with Cam/Crank if computer needs a Cam sensor input, Cam sensor was mounted behind AUX gear so needed to be timed to Cam, Cam sensor were used in 1995 and up, but earlier if a vehicle was originally sold in California, Calif. Emissions

But yes you can put the "mark" at 12:00 when setting up the other gears timing

Cam gear and AUX gear are interchangeable, same part, newer gears would have both marks, triangle and diamond, older just needed the one mark

 

Thanks for the help on this. I put it all back together, and it's running like a champ! Turns out jumping three teeth on the timing belt leads to poor engine performance. Who knew?