The search continues for my mysterious surging idle/stalling issue

[RustyDusty]

While I had the EGR valve off I made a crude little steel block off plate and installed it on the intake where the egr attaches to it and plugged the egr tube, disconnected the vacuum line to the EGr solenoid and plugged it and started it up and it still surges. when I unplug the egr tube I can feel the exhaust coming through. Seems like the EGR system isn’t causing this as far as I can tell.

 

[rusty ol ranger]

While I had the EGR valve off I made a crude little steel block off plate and installed it on the intake where the egr attaches to it and plugged the egr tube, disconnected the vacuum line to the EGr solenoid and plugged it and started it up and it still surges. when I unplug the egr tube I can feel the exhaust coming through. Seems like the EGR system isn’t causing this as far as I can tell.

When you did this did you also unplug the pulse sensor?

One other thing i just thought of....hows the hard plastic vacuum tube going to the MAP?

I had some weird issues i couldnt pin down and found mine had a leak (i put my finger on one end and blew in the other, and i was able to keep blowing)...doubt thats it but maybe something to check.

You said you bought a new ECM? Where did you buy it? Does it have a warrenty?

If youre fairly certain its not EGR or knock sensor related thats really about the only other variable the 89 ecm would knock out of contention.

 

[RustyDusty]

When you did this did you also unplug the pulse sensor?

One other thing i just thought of....hows the hard plastic vacuum tube going to the MAP?

I had some weird issues i couldnt pin down and found mine had a leak (i put my finger on one end and blew in the other, and i was able to keep blowing)...doubt thats it but maybe something to check.

You said you bought a new ECM? Where did you buy it? Does it have a warrenty?

If youre fairly certain its not EGR or knock sensor related thats really about the only other variable the 89 ecm would knock out of contention.

The pulse sensor was unplugged.

The vacuum line to the MAP sensor is new and holds vacuum.

The ECM is from Rockauto. I believe Cardone remanufactured it. I'm not sure if there's a warranty, I can look into it.

I'm pretty stumped yet again. I just rebuilt the carburetor on my 80's Toyota landcruiser in between working on the ranger. The Toyota's running so damn well and a carburetor's so much easier to wrap my head around. I'm hating fuel injection at the moment haha.

 

[Shran]

When I first got my '87 it had a horrible surging idle (5 speed truck.) It does have EGR and the problem eventually just went away? Was really weird. The only thing I can attribute it to was bad fuel/partially failed fuel pump/etc. It sat for 10+ years and did not like running off the old fuel. I cleaned out the tank and replaced the pump, sending unit, and filter but I think I left the high pressure pump in place since it worked. I had a horrible surging idle for quite a while and it eventually just cleared up.

Not that any of that helps you, just my experience. This is certainly fixable, just a matter of time and narrowing down the cause.

Glad to see that your EGR valve isn't stuck. Exhaust gas coming up through the tube is normal. Have you tried applying vacuum to the vacuum port on the EGR valve while the truck is idling? I think you should be able to watch and see how it moves and it should immediately affect how the engine runs. Can you verify that it closes completely as it should?

 

[RustyDusty]

When I first got my '87 it had a horrible surging idle (5 speed truck.) It does have EGR and the problem eventually just went away? Was really weird. The only thing I can attribute it to was bad fuel/partially failed fuel pump/etc. It sat for 10+ years and did not like running off the old fuel. I cleaned out the tank and replaced the pump, sending unit, and filter but I think I left the high pressure pump in place since it worked. I had a horrible surging idle for quite a while and it eventually just cleared up.

Not that any of that helps you, just my experience. This is certainly fixable, just a matter of time and narrowing down the cause.

Glad to see that your EGR valve isn't stuck. Exhaust gas coming up through the tube is normal. Have you tried applying vacuum to the vacuum port on the EGR valve while the truck is idling? I think you should be able to watch and see how it moves and it should immediately affect how the engine runs. Can you verify that it closes completely as it should?

It's helpful to hear stories of people overcoming their truck's surging idle. That's funny your issue just went away. The same thing kind of happened to my '89 Econoline. It had this same damn issue and it drove me nuts sometimes but it would go away and return and I now cant remember the last time it did it. When we got this ranger and it did the same thing I thought well shit it must be a ford quirk. I even asked some mechanics if they've noticed if a lot of old fords they work on have surging idles and they said definitely.

I replaced the high pressure fuel pump and fuel filter when I first got the truck because it was dying randomly and I couldn't hear the pump prime when Id turn the key at times. New fuel pump didnt fix the issue and I later learned the issue was a faulty ignition switch. I havent touched the in-tank pump so I don't know the state of that one but my fuel pressure is within spec so I'm doubtful its a fuel issue. This truck's my daily driver so its constantly getting fresh fuel.

This truck also sat for years before the previous owner purchased it from a neighbor. The truck was a father son project. It had a blown head gasket so they took the engine apart, put in new valves, new heads and gaskets, water pump, radiator, timing chain, injectors, egr valve, catalytic converters, brakes, brake booster, master cylinder, shocks, fuel pressure regulator, IAC, TPS, MAP, TFI, O2 sensor, belts, hoses, tires, manual locking hubs they went all out and the son got bored with it so the dad sold it to my girlfriend and I for $2k. He was kind of relieved to be done with it haha. I don't have it in my notes that they replaced the in tank pump or cleaned the tank so I guess I don't really know whats going on in there. I'd assume with all the work they did they know they'd have to do something about the tank on a truck thats been sitting.

I checked the EGR by blowing through one hole and plugging another (cant remember which combo it was now) and without vacuum applied to the vacuum port I couldn't get any air through. When I applied vacuum the valve opened I could then blow air through. Yeah I've also applied vacuum to the EGR with it running and the truck immediately stumbles and If I remember correctly it stalls. This was a test I did in the early days trying to troubleshoot the EGR system.

 

[rusty ol ranger]

I would look intp doing a warranty exchange on that ECM

 

[RustyDusty]

Alright so I'm using the warranty on the new ECU to get a replacement. Should arrive in a week or so, fingers crossed thats the problem but for some reason I'm doubtful. I ran an errand in the truck today that involved a 45 minute drive on the freeway, parked went into a store and 15 minutes later came out and the truck died immediately after starting it, so I started it again, died again, and again and again 10 times in a row. finally on the 11th time when the idle dropped the engine just barely saved itself and I quickly put it in gear and went back home. I'm tired of just accepting this and am motivated to solve this problem.

I'm really surprised I haven't nailed it by now but I'm guessing it's a case of a new part being bad out of the box. Just not sure which one it is. ECU will be the first part to swap. I'm also wondering about temperature related sensors like the ECT and ACT. I'm wondering what parts/sensors would be your guys' top suspects if we were to forget about the '89 computer that fixes my issues. How do I go about solving this issue without just throwing parts at it? What parts would let the truck run great when cold but completely mess up during warm idle?

According to this website the sensors in use during warm idle are PIP / MAP/ ECT / ACT / TPS / EGR / NDS / HEGO. Truck has a new PIP sensor/distributor, I've tried 3 different MAP sensors, 3 different TPS, I've only put one new ECT sensor and one new ACT sensor on, havent touched NDS. Two parts I haven't replaced myself but were new on the truck when I got it 2 years ago are the EGR sensor and the HEGO. I did test the O2 sensor when I was first trying to track down this problem and even threw the one from my van on without any change to the issue. Should I reinvestigate that part? If so what's a reliable test? Anyone have any new ideas while I wait for the new computer?

 

[rusty ol ranger]

If the 89 ECM fixes it its the ECM, knock sensor/system or the EGR.

Those are the ONLY differences. It seems youve ruled out both the EGR and knock.

 

[RustyDusty]

Well I received the warranty replacement computer in the mail, installed it in the truck and warmed up the engine. First impressions were it was running well and not surging. I took it for a 10 minute drive and when I got back put it in park, still seemed good although I noticed some variation in the RPMS. I shut the truck off to try starting it warm and it the RPMs did immediately drop but it didn't stall. I kept messing around like this for a while seeing if I could get the symptoms back and while they're not as severe as before I think they might be coming back. Sometimes after disconnecting the battery and wiping the computer it runs better at first but in a day or so Im back to where I began. Im guessing because the computer learns how to run the truck like crap again. Anyways I'm not jumping to conclusions yet but I'm not hopeful that the problem was resolved with a new computer.

There is a ground wire coming from the ECM wiring harness thats screwed into the sheet metal next to the computer. Doesn't look factory, curious if anyone can confirm this is legit location for this ground or does it need to go to the ECM directly?

Just for the hell of it I did RonD's suggestion again of unplugging the IAC, setting the anti-diesel screw to get the RPMs around 750-800 and to drive around like that. The RPM's still fluctuated between 500-800 at times in the familiar rhythm thats been haunting me but shutting the truck off and starting it warm didnt cause it to die like usual. At some point while reversing the truck died which is extremely unusual, I can't remember I time its ever done that. Made me scratch my head. Anyways just thought I'd throw that out there in case that points to something we haven't thought of yet.

 

[rusty ol ranger]

That wire is stock. Its on my 87 to.

If it runs good with the 89 ECM id just run it with that computer.

 

[Angie]

have you unplugged the power brake booster and then plugged that hose back up to dismiss the booster being shot full of holes and getting a vaccuum leak or 2 in the booster?

 

[RustyDusty]

have you unplugged the power brake booster and then plugged that hose back up to dismiss the booster being shot full of holes and getting a vaccuum leak or 2 in the booster?

Yep, doesnt make the symptoms go away

 

[RustyDusty]

That wire is stock. Its on my 87 to.

If it runs good with the 89 ECM id just run it with that computer.

Problem is the truck won't go into overdrive with the 89 computer due to there being 2 shift solenoids in the '89 and only one in my '87.

 

[Josh B]

Is there any way to rig it to manually hit overdrive?

 

[90B2]

Three things can cause idling engine to surge, more air or more fuel or spark advance change

IAC unplugged, warm engine

Timing light on engine, should be 20-22deg BTDC on warm engine, see if it changes prior to surge
If so disconnect SPOUT and retest, if timing is stable at 10-12deg BTDC then computer's timing advance is causing it

Test fuel pressure while its surging, 30-35psi is expected
Also remove vacuum hose from FPR and plug the hose, retest fuel pressure, 41-43psi is expected


A4LD, pre-1989, will have a vacuum hose to intake, longshot, but check that hose for fluid, at high vacuum, idle, it could be sucking in ATF

If it were sucking in atf it would be smoking out the tail pipe. He doesn't mention that...