Extremely rough idle 92 Ranger 4.0l

[mikey67156]

Specs: 1992 Ranger 4.0l Manual trans 2WD.

Long post. Sorry but I wanted it all out there.

About a month ago the pickup started running rough. Just a rough inconsistent idle, and weak throttle response (no CEL). This was coupled with a corroded freeze plug on drivers side rear cyl. head. At this point I decided that because I had leaky valve cover gaskets and no cherry picker that I would just remove the cylinder head and change the freeze plug that way.
Everything went back together nicely. Upon first start I realized that the engine now runs like well... crap. uopn cranking engine starts revs about a second, then without help it dies. If you bump the gas it stays running, but only with constant throttle nudging, and still just barely stays running. After about 10 minutes of babying it, it runs on its own, albeit with a high idle. Could it be that the PCM has a null setting, and it just doesn't mesh till it warms up?

Checked sparkplug wire order according to the (terrible) pic in the Haynes Manual they seem right
Had 4 different guys do a flashlight exam for disconnected wires (hey it happens)
Ether tested vacuum lines

Performed KOEO got 34. Continuous memory showed 157, 158, 543, 556. I was unplugging MAF earlier while it was running.
KOER 173, 411, 412. Cylynder balance test was impossible to run because of the erratic idle (the ONE I really wanted to run.
Components checked: Ohms/Volts respectively. MAF, IAC, TPS, IAT (showed bad, replaced no change in performance) Feul pressure regulator, stethoscoped injectors they sounded fine, nice steady rhythm that is.

I'm baffled I'm a 4.9l guy. Usually you just throw an IAC at it and your back down the road.

Thanks for any help,
Mikey

 

[MrShorty]

Checked sparkplug wire order according to the (terrible) pic in the Haynes Manual they seem right

Where you recently had the engine apart, I think you need to be more certain that you have them on right. If the diagram/description in Haynes is inadequate, then find another one (I know someone has posted firing order information for the early 4.0's on here that seemed easy to understand and follow).

Performed KOEO got 34.

double check this. You should be getting a three digit code KOEO just like you did CM and KOER. 3xx codes on these tend to be EGR codes -- did you get the EGR system hooked back up correctly?

Continuous memory showed 157, 158, 543, 556. I was unplugging MAF earlier while it was running.

If you clear CM, run the engine for a bit, then re-test, do the MAF codes go away? The CM 543/556 codes (especially in the absence of equivalent KOEO codes) indicate an intermittent fault in the fuel pump circuit. Or maybe you unplugged the fuel pump relay or fuse while running as part of some diagnostic steps. If these codes come back, you might check the fuel pump wiring for loose connections.

KOER 173, 411, 412.

KOER 173 points to a rich running engine. Does it act like it's running rich? Have you checked fuel pressure? How did you check the FPR when you checked it?

 

[mikey67156]

Thanks for the help!

Where you recently had the engine apart, I think you need to be more certain that you have them on right. If the diagram/description in Haynes is inadequate, then find another one (I know someone has posted firing order information for the early 4.0's on here that seemed easy to understand and follow).

I double checked the firing order, and I had it correct. It would have been nice if that's all it was lol. I was hoping for an easy fix here.

double check this. You should be getting a three digit code KOEO just like you did CM and KOER. 3xx codes on these tend to be EGR codes -- did you get the EGR system hooked back up correctly?

From what I read there is no EGR valve on the 91-93 4.0l. Is there anything else that may apply?

If you clear CM, run the engine for a bit, then re-test, do the MAF codes go away? The CM 543/556 codes (especially in the absence of equivalent KOEO codes) indicate an intermittent fault in the fuel pump circuit. Or maybe you unplugged the fuel pump relay or fuse while running as part of some diagnostic steps. If these codes come back, you might check the fuel pump wiring for loose connections

I disconnected the neg battery cable and then reran KOEO and got 111's.

All I did to check the fuel pressure regulator was run the engine and after shutdown check the vacuum line for fuel leakage. I haven't checked fuel pressure yet. I'll have to borrow a gauge set tomorrow and check it out.

 

[MrShorty]

From what I read there is no EGR valve on the 91-93 4.0l. Is there anything else that may apply?

'91 and '92 don't have EGR systems. I haven't pinned down exactly which '93's did and which didn't, but some '93's have EGR systems and some don't. I expect it, in part, has to do with CA vs. Fed emissions and such. All I know is that some '93's have an EGR system. I think when I posted this, I was operating under the mistaken impression that you had a '93 (I have no idea where I got that idea).

 

[92exp4x4]

Calif emissions included EGR, a cam position sensor (Cylinder identification sensor) and dual HEGOs. It was optional in 93, standard on Calif sold trucks, then standard across the board in 94. My 93 has cali em on it. I think it was sold new in Arizona.

 

[mikey67156]

I am finally getting somewhere. I changed the fuel filter today. I just wanted to eliminate something so simple and easy.

I also got the engine warmed up a little, and got it to idle steady(ish). I then started disconnecting spark plug wires. I started with #4. No change. Then I did #5. No change. Then I did #6, and there was no change. At this point I had the whole left bank (aft looking forward) unplugged and the idle didn't change any. The plugs and wires are new, and spark is strong. That just leaves fuel. It looks to me like the tan wire coming off pin 59 on the PCM is the culprit, at least somewhere in that wire. I'll start ohms checking it in the morning.

Does this sound like the proper course of action?

 

[mikey67156]

Never mind I am nowhere...

Checked fuel injector wiring from EEC to injectors (white wire NOT the tan as I said earlier @ pin 59) and it shows 1 OHM resistance from EEC to #4, 5, and6,s white wire. The red wire on each shows 14.4v. Same as the right bank which is working fine. I didn't know how to check the white wire from the EEC to see if it is doing what it is supposed to be doing.

I aslo pulled the plenum off today so I could pull the harness out and check for obvious damage. I found none. What I did find however is that each of the intake runners for the non firing cylinders had fuel pooled in the bottom. I have no idea what the heck this means. It would seem to mean that perhaps I am getting fuel.

I swapped my ignition coil out with a known good coil and had no luck fixing the idle.

How the heck should I proceed?

 

[mikey67156]

Never mind I am nowhere...

Checked fuel injector wiring from EEC to injectors (white wire NOT the tan as I said earlier @ pin 59) and it shows 1 OHM resistance from EEC to #4, 5, and6,s white wire. The red wire on each shows 14.4v. Same as the right bank which is working fine. I didn't know how to check the white wire from the EEC to see if it is doing what it is supposed to be doing.

I aslo pulled the plenum off today so I could pull the harness out and check for obvious damage. I found none. What I did find however is that each of the intake runners for the non firing cylinders had fuel pooled in the bottom. I have no idea what the heck this means. It would seem to mean that perhaps I am getting fuel.

I swapped my ignition coil out with a known good coil and had no luck fixing the idle.

How the heck should I proceed?

 

[Joes4x4Ranger]

Check compression in those 3 cylinders.

 

[92exp4x4]

The fuel was pooled around the valves? Are the pushrods installed correctly or even in the motor? Is there a priming procedure for the hydraulic lifters? Dumb questions but it might be possible that they were forgotten. The forklifts i worked on had a bleeding procedure you had to do when putting new lifters in.

Based on how i read your post, I think the valves are not opening. It sucks to have to tear down the motor after doing all that work, but i think it may be necessary.

 

[92exp4x4]

Rotate the motor and see if the intake valves move at all. If not, check the rocker arms for tightness or damage. If they are good, pull the intake manifold and see if the pushrods and lifters are present and in good shape. I can't see anything else being a major problem, other than the injectors themselves. They could be stuck open or have crap in them. Check to see if they dribble fuel while the system is at regulated pressure.

Again, I am assuming that all parts were put back, but I have gotten ahead of myself before and forgotten stuff. It can happen to anyone.