The search continues for my mysterious surging idle/stalling issue

[RustyDusty]

88+ 2.9s did NOT have a EGR.

The 89 ECM basically bypasses the EGR and the knock sensor, as the knock sensor went away with the 88+ models as well.

I would pull the EGR valve and see if its stuck open, or if the passage behind the EGR is plugged with carbon. My 87 was plugged rock solid.

Also it could be an issue with the EGR vacuum solenoid (the little can on the passenger side with little red and green vacuum hoses running to it, as well as a plug)

There is also an EGR pulse sensor, that tells the ECM what the EGR is doing. Its a little black box held on by two clips right in the vicinity of the EGR valve. There is a little hose running to the bottom side of it from the EGR valve, and an electric plug

Also, do not overlook the knock sensor. Its job is to adjust timing if it senses spark knock. However, if you have alot of valvetrain noise (ticking) it will sense this as spark knock and retard timing.

The sensor itself could also be failing.

Since the 89 ECM clears everything up i would bet on either...

1- EGR valve/system issue
2- Knock sensor issue/valvetrain noise
3- Failed ECM.

Listed in order of which is most likely to least likely.

The knock sensor is something I haven’t checked out yet, I don’t even know where it is or what it looks like. One thing that makes me question that theory is that I just checked the timing and its consistent doesnt change with the surging idle. So I doubt the surging is caused by timing being retarded by the knock sensor. Is there something I’m missing with the knock sensor theory?

EGR system is definitely the #1 suspect in my mind at the moment since Ihave noticed the EGR vacuum valve solenoid makes a whining/rattle noise that I can hear with the hood popped after I shut off the engine. The sound is vacuum leaking from the top cap/filter. Can anyone verify if this-means it’s defective or if it’s normal for these things? I have never removed the EGR valve but I have tested its operationby pulling vacuum on the valve and the diaphragm works and holds vacuum.It seemslike it’s time to actually take it off and make sure the hoses aren’t clogged. The EGR pulse sensor looks like it was replacedby the previous owner. A lot of parts that I’ve looked at were replaced because I’m guessing they were trying to track down this same exact issue and gave up as I have done several times now. When I take off the hose to the pulse sensor there is air being pumped out of the hose. Is there a way to test the pulse sensor?
One problem I have with the EGR system being the problem is that I felt it got shut down earlier in this thread because it was stated that the EGR system isn’t active during idle. Is that true? Or is it still being used in some capacity during idle?

 

[RustyDusty]

I’d like to try to recap all the potential issues discussed they haven’t been ruled out.

• EGR system (clogged lines, valve not closing completely, faulty valve solenoid etc..)
• Faulty Computer
• Vacuum leak
• Electrical issue (bad ground, wire shorting, alternator issue etc..)

Is there anything I’m missing/forgetting?

 

[rusty ol ranger]

The EGR i dont believe is supposed to be active at idle no. But if somethings screwy in its operation it could very well be working at idle when its not supposed to.

Im not sure of any way to check the pulse sensor.

If the timing stays normal (sorry, missed that part) i would say you can rule out the knock sensor.

If the EGR valve seems to be working properly then honestly i would replace the vacuum solenoid. Ive never noticed one making noise after shutdown. That being said ive disabled my EGR by going with an 88 ECM.

You might could try unplugging the 2 vacuum hoses that run to the solenoid (unplug them at the motor), capping off the ports, and starting it after its warm just to see if it changes the idle.

I dont believe the vacuum solenoids are that expensive. If thats not the cause then it could be the wiring to it or some goofy ECM issue.

 

[RustyDusty]

The EGR i dont believe is supposed to be active at idle no. But if somethings screwy in its operation it could very well be working at idle when its not supposed to.

Im not sure of any way to check the pulse sensor.

If the timing stays normal (sorry, missed that part) i would say you can rule out the knock sensor.

If the EGR valve seems to be working properly then honestly i would replace the vacuum solenoid. Ive never noticed one making noise after shutdown. That being said ive disabled my EGR by going with an 88 ECM.

You might could try unplugging the 2 vacuum hoses that run to the solenoid (unplug them at the motor), capping off the ports, and starting it after its warm just to see if it changes the idle.

I dont believe the vacuum solenoids are that expensive. If thats not the cause then it could be the wiring to it or some goofy ECM issue.

I have tried capping both vacuum hoses that run to the EGR solenoid and it didn’t affect the surging idle unfortunately.

Does your truck have the A4LD with only one solenoid? If so I might want to try an ‘88 ECM as well. Where I’m located now I don’t need to smog this truck ever again so disabling the EGR system would be fine with me if it fixes this surging idle issue.

 

[rusty ol ranger]

I have tried capping both vacuum hoses that run to the EGR solenoid and it didn’t affect the surging idle unfortunately.

Does your truck have the A4LD with only one solenoid? If so I might want to try an ‘88 ECM as well. Where I’m located now I don’t need to smog this truck ever again so disabling the EGR system would be fine with me if it fixes this surging idle issue.

No my truck is a 5speed.

I dont think the trans would have anything to do with this. I seen it brought up earlier, the only way i could see the trans playing any part would be if the vacuum hose going to the modulator is bad.

Was the 89 ECM from an auto truck? I believe all the ECM controls on the A4LD is lockup.

You said it shifted hard into 3rd with the 89 ECM?

 

[RustyDusty]

No my truck is a 5speed.

I dont think the trans would have anything to do with this. I seen it brought up earlier, the only way i could see the trans playing any part would be if the vacuum hose going to the modulator is bad.

Was the 89 ECM from an auto truck? I believe all the ECM controls on the A4LD is lockup.

You said it shifted hard into 3rd with the 89 ECM?

My ‘87 only has one shift solenoid and A4LD’s on ‘89 rangers have 2 solenoids. So as far as I understand the ‘89 ECM won’t shift my truck into overdrive because it relies on a solenoid that my transmission doesn’t have. I’ve never put my truck into overdrive with the ‘89 computer because I don’t want anything funky to happen. My truck shifts great with the ‘89 ECM but like I said I don’t do overdrive.

The hard shifts I was mentioning earlier was unrelated to the computer issue. It was happening since I bought the truck with my original ECM and it was because of a dirty valve body. I opened it up, cleaned every valve and check ball and checked the function of the solenoid. I put it back together with a new modulator and it didn’t shift with that modulator (i didn’t do any adjustments to it so that’s probably the issue). So I put the original modulator in to trouble shoot and it shifted perfectly (Going from park to drive/reverse was still harsh, probably due to slop in my diff. Possibly the modulator could use adjusting as well?)

 

[RustyDusty]

@RonD I’m curious if you watched my video of my truck idling and if so do you agree the trucks not running right while warm? Is that what you’d call surging?

 

[rusty ol ranger]

I dont know alot about auto trannys in general. I dont think the modulator would cause a harsh gear engagement though. Modulators only control the actual upshifts.

Have you tried pulling codes?

Maybe take the cover off your 87 ECM and see if there is any obvious signs of damage?

I did watch your video and i would for sure class that as surging.

Im really startin to wonder if you just have a bad ECM

 

[RonD]

Yes, that's surging not a "lope" you can get with worn or oversized cam

But IAC Valve should smooth that out a bit when its plugged in, computer is pretty fast to react to RPM changes

When its in R or D does the surge go away?

 

[RustyDusty]

Yes, that's surging not a "lope" you can get with worn or oversized cam

But IAC Valve should smooth that out a bit when its plugged in, computer is pretty fast to react to RPM changes

When its in R or D does the surge go away?

The IAC Valve doesn't really help unfortunately, at least not in Park. The Surging does go away in Reverse or Drive. Here's a video perfectly showing what starting this truck warm is like (note: all sensors, valves, wires, hoses etc.. are connected and this is with my new ECM made for this truck). Before I shot this video the truck actually died on me 5 times in a row before it would stay idling. At the end of the video I put the truck in Drive and you will notice the surging goes away.

http://imgur.com/a/hmxRwom

 

[RustyDusty]

I dont know alot about auto trannys in general. I dont think the modulator would cause a harsh gear engagement though. Modulators only control the actual upshifts.

Have you tried pulling codes?

Maybe take the cover off your 87 ECM and see if there is any obvious signs of damage?

I did watch your video and i would for sure class that as surging.

Im really startin to wonder if you just have a bad ECM

Yep I often pull codes before I disconnect the battery just to see if anything new/interesting pops up. I normally don't have any but I mentioned earlier that I got a code for the PIP sensor and I was excited I might have found the issue. I replaced the whole distributor and I havent seen the PIP code since but I still have the surging.

My original ECM was actually immaculate, looked brand new, no corrosion or leaky caps. I really had no reason to believe the computer was bad but when I finally gave in and took my truck to a shop the guys there were all completely stumped and said the only thing they didnt really test for is a bad computer. At that point I tested the voltage of the important pins on the ECM to make sure there wasn't some sort of wiring issue first and when it all checked out I got my hands on this '89 ECM just to give it a shot and see if anything changes before I buy a new one made for my truck. When my issues disappeared with the '89 ECM I thought bingo! it was the computer all along! I ordered a new remanufactured Ford ECM for my specific truck and the problem returned with that new ECM. Thats where I'm at now. I'm really not trying to buy more ECM's on a hunch but its starting to look like the signs are pointing in that direction.

 

[rusty ol ranger]

It acts like a lawnmower with a carb issue, where it leans out untill you put load on and the governor feeds it fuel.

I think its EGR related after reading that last post of yours.

The ONLY difference between the 87 and 89 ECM is the knock and EGR.

EDIT-

Have you tried spraying starting fluid around the upper intake gasket to see if its leaking anywhere?

 

[RustyDusty]

It acts like a lawnmower with a carb issue, where it leans out untill you put load on and the governor feeds it fuel.

I think its EGR related after reading that last post of yours.

The ONLY difference between the 87 and 89 ECM is the knock and EGR.

Have you tried spraying starting fluid around the upper intake gasket to see if its leaking anywhere?

Are those the only differences? I know another difference is the shift solenoids as I mentioned but sounds like that’s pretty irrelevant to my situation.

yeah I have tried spraying around the intake gasket.

I’m going to go ahead and take apart the EGR valve and lines and see if I find anything unusual.

 

[RustyDusty]

Here's a video of that EGR solenoid making it's noise letting out vacuum after I shut the truck off. I'll definitely pick up a new one of these or at the very least try a junkyard one out. I've sort of assumed it can't be my issue since the symptoms are there whether the vacuum line is hooked to it or not.

http://imgur.com/a/E0x25nr

Thanks everyone for taking time out of their day to help me with this issue.

 

[RustyDusty]

I just took off the EGR valve. Nowhere near being clogged. Diaphragm moves nicely, I don’t see anything wrong with it. The EGR pipe to the exhaust manifold looks clear too, I can’t imagine it being clogged further down the pipe but the thing that is unusual about it is it’s loose where it attaches to the exhaust manifold. The large nut is there but the pipe moves around. I tried loosening and tightening the nut but it’s on there pretty good and that’s a hell of a place to fit a wrench big enough for that but. Is it possible the loose nut is creating an exhaust leak that’s causing my problems? Not sure why a different computer would fix that though.