92 22RE 4WD 5SPD - Stumble/Miss - Lots of Detail & Troubleshooting done. Need help.

[ShortySMC]

Hi - First Post Here....

Ok. I have a 92 22RE 4WD 5SP
Picked it up from a buddy about a week ago.

It is stumbling/missing. No codes present.

WHEN IT IS IN COLD START MODE IT RUNS FINE
When it passes cold start, it stumbles/misses under load.
I can clear it by flooring it and easing back, until it does it again, and repeat.
It is persistent.
IF I UNPLUG THE TPS SENSOR IT RUNS SMOOTH WITH NO STUMBLE OR MISS.... ?????

Here's what I've done:

New Cap, Rotor, Wires, Plugs, Fuel Filter
Verified good battery contacts and engine grounds.
Tested Ignition Coil, Good.
Tested Volume Air Flow, Good.
Tested Intake Air Temp, Good.

Tested Throttle positioning sensor on OHMS, and it reads up to 3/4 or so and has a spot that drops then comes back above it.
I got a used one, tested the same way, installed it, same thing.
Not sure if that's it or not, and a new one locally is $100
Not sure if I wanna spend it yet without knowing if that's it or not.

Am I missing anything major I should be checking?

What about the ECT - Coolant Temp Sensor...?
Manual doesn't have a location. Radiator? How do I test it?

I can unplug the TPS and it runs fine - with the service engine light on.
Plug it in, it stumbles/misses under load - floor it and ease back to clear it 'momentarily' for an inconsistent amount of time.

So... either something related to the TPS/ECM?,
or, something with fuel or something related to cold start?

Looking for some help, because I am beyond what this Chilton offers me for testing.

Thanx - First Post

Shorty

(Not sure if it's notable, but my buddy used Platinum +2 4036 Plugs, which show being ok for this truck, but just curious)

[ShortySMC]

Also, what is the valve on the engine side of the Air Intake Chamber?

Located around the center of it. Tall Screw/Bolt sticking out the top with a spring to keep it in place.

Vacuum lines coming off it so I'm assuming the valve dials in vacuum??

I don't see anything for this in the manual and so I'm not sure of it's significance or where it should be set.

Truck has 190k on it, but the engine is a rebuild with only 30K on it done by a professional shop in WA, but a lot of the stuff that went back on the long block is original to the truck. So there are a lot of what ifs.

Thanx, really need to get this figured out without spending a fortune.

[ShortySMC]

In regards to the Fuel Pressure Regulator:

Page 4-28 of the Chilton manual shows a 'VSV (for AS)'
What is that?

I am thinking that is the 'module' that the ECM controls to regulate vacuum in order to effect Fuel Pressure?

Because it runs fine under cold start, with the TPS plugged in, it is getting more gas, and so I am thinking maybe I have a Lean condition once cold start stops, causing it to stumble - with the TPS plugged in.

Removing the TPS plug corrects this, which I don't really understand, but I am wondering about the Fuel Pressure Regulator, and that VSV ???

Sorry to keep kicking this, but I'm really at a loss.... Racking my brain here.

At idle, removing the plug from that VSV seems to have no effect.
I will drive it with it disconnected and see how that effects things.
Also, removing the vacuum line from the Fuel Pressure Regulator had no effect, at idle.

[ShortySMC]

Unplugging the vacuum from the Fuel Pressure Regulator makes no difference.

Unplugging the O2 sensors makes no difference either.
I tried testing them, per the manual, but it isn't specific as to which lead to test.
I ran thru em all, and I got nothing that was responding like the manual said it should.

Manual says they should fluctuate rapidly between .4 and .6 volts. I didn't see that.

I can't find any vacuum leaks either.

???????????

This is killin me.

Like I said, disconnecting the TPS corrects the stumble, but it appears to be going through more gas too.

[ShortySMC]

Ok, crimped the return line to the tank off the Fuel Pressure Regulator, thereby increasing fuel pressure, and she ran fine.

So. Either the Fuel Pressure Regulator is stuck open, or the fuel pump is weak.

I gather I am correct to assume that it is OPEN at High Vacuum (Idle) and CLOSES off variably at Low Vacuum (Higher RPMs) ??
I do have good vacuum on the line operating the regulator.And, as I said earlier, removing the vacuum line from the regulator had no effect.
So I am thinking - it's stuck open, therefore NOT increasing the fuel pressure..... OR it is operating properly, or not and is stuck closed, but the fuel pump is weak and therefore not delivering enough pressure.

So I think this is right.... Stuck OPEN, or working fine or stuck shut AND Fuel Pump is weak.

I'm gonna take it off and see if it is maybee obstructed or if I can get her workin.


At this point I am just gonna wrap this thread up with the conclusion/solution when I get there (Tonight/Tomorrow)
Just for the benefit of others with theirs behaving the same way, with the same symptoms.

Wish I had thought to crimp the return line earlier. This would have saved me some money, time, and trouble.

[RoyL]

Originally Posted by ShortySMC

Ok, crimped the return line to the tank off the Fuel Pressure Regulator, thereby increasing fuel pressure, and she ran fine.

So. Either the Fuel Pressure Regulator is stuck open, or the fuel pump is weak.

I gather I am correct to assume that it is OPEN at High Vacuum (Idle) and CLOSES off variably at Low Vacuum (Higher RPMs) ??
I do have good vacuum on the line operating the regulator.And, as I said earlier, removing the vacuum line from the regulator had no effect.
So I am thinking - it's stuck open, therefore NOT increasing the fuel pressure..... OR it is operating properly, or not and is stuck closed, but the fuel pump is weak and therefore not delivering enough pressure.

So I think this is right.... Stuck OPEN, or working fine or stuck shut AND Fuel Pump is weak.

I'm gonna take it off and see if it is maybee obstructed or if I can get her workin.


At this point I am just gonna wrap this thread up with the conclusion/solution when I get there (Tonight/Tomorrow)
Just for the benefit of others with theirs behaving the same way, with the same symptoms.

Wish I had thought to crimp the return line earlier. This would have saved me some money, time, and trouble.

Did you solve the stumble problem? Pressure regulator or fuel pump, or otherwise?