Bad Idle ECU?

[Trstno1]

Hey guys -

This winter I have decided to dive right into the right of passage that is the dreaded VOD teardown & cleaning. First, I must admit that I was lucky since I broke nothing getting things down to the VOD!! On top of not breaking anything, the VOD was very dry with just accumulation of what appeared to be sand and a couple random pieces of wood. Awesome!!

:jawdrop: I know, right...

I'll be replacing the following items in hope of finally getting 5625 to run correctly:

Cleaned out fuel tank
New combo DMC fuel pump/sender
Fuel Filter (DMCH)
SS Fuel lines (DPI)
Cleaned fuel injectors (Special T)
Mixture screw in the AMU - the PO drilled into it and now no tool known to man can get into it to adjust it. (DMCMW)
Cap (Special T)
Rotor (Special T)
coil (Special T)
Spark plugs (Special T)
Spark plug wires (Special T)
New ISM (EBAY)

Though in tearing the engine down, I realized I had a seized ISM. (my rough shaky idle was starting to make a little more sense). I have since ordered a new ISM because cleaning it did absolutely nothing. However, I am concerned about installing it right off when I put things back together. I have read many posts stating that a seized ISM can fry the Idle ECM. What about the other way around. Will a potentially fried Idle ECM take out my expensive new ISM? If not, I guess I just have to cross my fingers on startup and hope that it works... What do you guys think?

[Bitsyncmaster]

I'm pretty sure a seized ISM will not blow the ECU. Now a shorted coil on the ISM will blow the ECU. A blown idle ECU should not damage and ISM. So I would just install the new ISM.

It is best not to change to many things at one time when doing your engine work. That way, it's easy to narrow down problems if they occur.

[Trstno1]

I'm pretty sure a seized ISM will not blow the ECU. Now a shorted coil on the ISM will blow the ECU. A blown idle ECU should not damage and ISM. So I would just install the new ISM.

It is best not to change to many things at one time when doing your engine work. That way, it's easy to narrow down problems if they occur.

Ok, so how can I test the old ISM to see if the coil is shorted? Will the 2 outer pins be shorted to the center pin?

Yeah, I truly didnt want to replace so many things at once and actually tried not to at first. I completed the fuel tank cleaning, new combo unit, and fuel filter prior to starting on the engine. Those installs were successful and resulted in no leaks and a running motor.

Hopefully the rest goes as planned.... :wrenchin:

[Trstno1]

Ok guys-

So I am happy to report that everything is back together and I have no fuel leaks!!

The problem I have is when I start the car it shoots up to 2k rpm and sticks there unless I unplug the ISM. Once I do that it goes down to about 800rpm at idle.

The idle micro switch is being activated. I attempted to unplug the idle ecu (plug closest to the middle of the car) and noticed no change with the high idle. If I unplug the on closest to the drivers door, the car idles way down sometimes and wants to die, or dies..... If I unplug the ISM itself, the throttle plate closes completely and the idle goes down to where it should be. If I plug it back in, the throttle plate slightly opens sucking a mass amount of air and the idle shoots strait to 2000k rpm.

Is there anything else I can test or is this pointing to a bad idle ecu?

[DMCMW Dave]

Ok guys-

So I am happy to report that everything is back together and I have no fuel leaks!!

The problem I have is when I start the car it shoots up to 2k rpm and sticks there unless I unplug the ISM. Once I do that it goes down to about 800rpm at idle.

The idle micro switch is being activated. I attempted to unplug the idle ecu (plug closest to the middle of the car) and noticed no change with the high idle. If I unplug the on closest to the drivers door, the car idles way down sometimes and wants to die, or dies..... If I unplug the ISM itself, the throttle plate closes completely and the idle goes down to where it should be. If I plug it back in, the throttle plate slightly opens sucking a mass amount of air and the idle shoots strait to 2000k rpm.

Is there anything else I can test or is this pointing to a bad idle ecu?

Bad ECU. The fact that unplugging it pulls the idle back down, and the plugging it back in sends it back up, typically means the motor is good. You have two ways to test it for sure - borrow another one from a local friend (probably tough in Alaska!) or send it to someone who can put it in a car and test it. I've done that a few times for customers, the only risk is that you send in a good one and it's good, and you end up paying for a bunch of shipping to test it. If it gets to the shop and it's bad, they would just send you a new one anyway.

It's probably repairable, as it seems to be able to control the motor, but something inside near the signal input is blown. But there isn't really anyone routinely doing such a repair.

PS before you do anything, recheck wiring continuity between the ECU and the motor. It is possible, and since you took a bunch of stuff apart, likely, that one of the connections at the motor or the bulkhead has backed out and could conceivably cause this too.

[Trstno1]

Thanks for the quick reply Dave!

What connections at the motor could be a culprit? Also is there a peticular way the ISM shout be installed direction wise. Could it potentially be mounted backwards? I'll check continuity of the wires from the ISM plug and the idle ECU.




Bad ECU. The fact that unplugging it pulls the idle back down, and the plugging it back in sends it back up, typically means the motor is good. You have two ways to test it for sure - borrow another one from a local friend (probably tough in Alaska!) or send it to someone who can put it in a car and test it. I've done that a few times for customers, the only risk is that you send in a good one and it's good, and you end up paying for a bunch of shipping to test it. If it gets to the shop and it's bad, they would just send you a new one anyway.

It's probably repairable, as it seems to be able to control the motor, but something inside near the signal input is blown. But there isn't really anyone routinely doing such a repair.

PS before you do anything, recheck wiring continuity between the ECU and the motor. It is possible, and since you took a bunch of stuff apart, likely, that one of the connections at the motor or the bulkhead has backed out and could conceivably cause this too.

[Trstno1]

Also for the record, the 3 pins on the ISM do have continuity between 3 pins on the plug closest to the door on the idle ECU.

[Trstno1]

Bump

Does anyone else have ideas on things to check that would be producing my high idle with the new ISM is plugged in? I would like to exhaust all possibilities prior to trying to find a new idle ECU.

ISM installed backwards?
Vacuum solenoid electrical plug plugged in upside down?
Bad idle ECU?
Any other components that are part of the idle system that could potentially be bad?

Any thoughts are greatly appreciated.

[PJ Grady Inc.]

Bump

Does anyone else have ideas on things to check that would be producing my high idle with the new ISM is plugged in? I would like to exhaust all possibilities prior to trying to find a new idle ECU.

ISM installed backwards?
Vacuum solenoid electrical plug plugged in upside down?
Bad idle ECU?
Any other components that are part of the idle system that could potentially be bad?

Any thoughts are greatly appreciated.

It sounds to me like you disturbed the idle switch connection in the VOD when you were working there. Did you disconnect the rubber booted idle switch to check the connections while you were nearby? If so you may have dislodged one of the two wires there. That would give you an open circuit which would bring the idle up to 2500 RPM or so but that can vary based on other engine settings compared to stock such as CO enrichment etc. I have successfully repaired connections there without pulling the intake but you need skinny fingers, exact knowledge of its location by feel, a bit of luck and a lot of patience....enjoy!
Rob

P.S. It's not a good idea to go plugging or unplugging an idle ECU for test purposes while the engine is running. Do that with the engine off to decrease the odds of frying the delicate ICU.

[Trstno1]

Yeah, upon further testing the idle thermistor is reading an open load at the wires at the idle ecu. I checked continuity of the thermistor wires from the idle ecu to the bulkhead connector in the engine bay and it's solid. So I guess that points toward a broken wire from the bulkhead connector to the thermistor or a Faulty thermistor right? If I bypass the thermistor by jumpering the wires at the idle ecu my idle goes right back down. So I guess this proves my idle ecu as good. I suppose I could have disrupted the wires going to the thermistor while doing my VOD work...lame. When thermistors go bad do they typically show an open load between the pins?

I guess I'll familarize myself with its exact location while letting the engine cool to see if I can get at that sucker without pulling the intake manifold. Not excited.......



It sounds to me like you disturbed the idle switch connection in the VOD when you were working there. Did you disconnect the rubber booted idle switch to check the connections while you were nearby? If so you may have dislodged one of the two wires there. That would give you an open circuit which would bring the idle up to 2500 RPM or so but that can vary based on other engine settings compared to stock such as CO enrichment etc. I have successfully repaired connections there without pulling the intake but you need skinny fingers, exact knowledge of its location by feel, a bit of luck and a lot of patience....enjoy!
Rob

P.S. It's not a good idea to go plugging or unplugging an idle ECU for test purposes while the engine is running. Do that with the engine off to decrease the odds of frying the delicate ICU.

[PJ Grady Inc.]

Yeah, upon further testing the idle thermistor is reading an open load at the wires at the idle ecu. I checked continuity of the thermistor wires from the idle ecu to the bulkhead connector in the engine bay and it's solid. So I guess that points toward a broken wire from the bulkhead connector to the thermistor or a Faulty thermistor right? If I bypass the thermistor by jumpering the wires at the idle ecu my idle goes right back down. So I guess this proves my idle ecu as good. I suppose I could have disrupted the wires going to the thermistor while doing my VOD work...lame. When thermistors go bad do they typically show an open load between the pins?

I guess I'll familarize myself with its exact location while letting the engine cool to see if I can get at that sucker without pulling the intake manifold. Not excited.......

I can't recall one ever going bad but after 35 years nothing is unbreakable right?. I'll bet you a pint the problem is at the thermistor connection but by all means check the bulkhead connections first as it's easier.
Rob

[DMCMW Dave]

I can't recall one ever going bad but after 35 years nothing is unbreakable right?. I'll bet you a pint the problem is at the thermistor connection but by all means check the bulkhead connections first as it's easier.
Rob

I've never seen a bad one either, but that connector on the thermistor has been a problem.

[Trstno1]

Alright guys-

I was able to look at the thermistor plug and sure enough, a pin had backed out causing an open load reading from the sensor. I fixed the pin, plugged it back in and my idle is now 775ish!! :rofl: Way to go Dave and Rob! Thank you!!

Now I notice when I start the car it directly shoots to about 1200 rpm then searches between 700ish rpm and 1200 rpm for 3-5 seconds until it settles at 775. The problem- every time I increase the engine rpm and take my foot off the accelerator is starts searching again for 3-5 seconds until it settles again. Is that searching fixed via co adjustment or is it directly related to the operation of the frequency valve and the lambda system? I am confident now that the idle control system is working. Though I'm not sure the lambda system is working. Are there tests I can conduct to prove one way or another? I would like to know that all systems are working prior to making a co adjustment.

When I first bought the car I never noticed the frequency valve buzz. I'm not exactly sure what it does, but mostly everything I read states that I should hear a distinct buzz from it. :umm: I noticed the plug had a nasty bend to it and was very corroded so I replaced the plug with a new one but nothing changed operation wise. When the engine is running I can pull the plug on the frequency valve but notice no difference in the way the engine runs. Testing the frequency valve shows about 3 ohms between the pins. What should it show? Does the frequency valve regulate fuel pressure?

Once again, any and all help is appreciated! The folks on this forum have been invaluable to my running restoration, and I am very grateful! Being in Alaska I am forced to be my own mechanic, but I love it!!

[Trstno1]

ok -

New news! After I fixed my idle system problem with the backed out pin from the thermistor and a new ISM, I wanted to test the lambda system to make sure that was working correctly. Since I purchased my car I have never heard a buzzing frequency valve so I was pretty sure my lambda circuit wasn't functioning. When I first started the restoration in 2014 I replaced my O2 sensor but that did nothing. This time around I pulled out the technical service manual and started troubleshooting.

1. I tested all pins going into the lambda ecu and everything tested out with the exception of pin #7. Thant pin showed a ground before I started the car and while running after cold start up. Looking at the diagram in the technical service manual it appears as that pin should only be receiving a ground when either the full throttle enrichment switch or thermal switch is activated. I unplugged both and tested for shorts to ground going through the bulkhead to the lambda ecu and everything tested fine. I then tested the operation of the full throttle enrichment switch and that tested fine at the ecu with the thermal switch unplugged. I tested the pin on the thermal switch and it was grounded. Does this show a fault with the thermal switch or is the thermal switch supposed to not show a ground when activated after the coolant warms up?

2. Once I started the car with the thermal switch unplugged w/ no ground on pin 7 - low and behold I have a buzzing frequency valve!! I also noticed the huge idle hunt I was experiencing upon startup or after I returned the throttle to idle was almost gone!! There is still some idle hunting, but not nearly as bad as before.

3. So, I guess the question would be of the operation of the thermal switch. Does it show ground until activated, or should it only show ground when activated? Next would be trying to fine tune the CO adjustment. I have checked and rechecked all vacuum lines including the pipe of agony and all seems well.

4. What do I need to do to get the engine to idle a little more smooth and cut down on some of the idle hunt that is left? I have to say that the car now idles better than it ever has but it still runs a little rough. The whole reason I replaced all these items were to finally get rid of the rough / rich running. I know I'm on the right path, I'm just not completely there yet.

(Side note. I have not replaced the WUR, I just made sure the mesh filter was clear of anything that shouldn't be there prior to hooking up the SS lines).

4. I created a video of my newest dwell readings. Ill post it here in a bit. Let me know if you guys see anything out of the ordinary.

[Trstno1]

Here's the video

http://youtu.be/qXqHotBThUM

[DMCMW Dave]

ok -

1. --- I tested the pin on the thermal switch and it was grounded. Does this show a fault with the thermal switch or is the thermal switch supposed to not show a ground when activated after the coolant warms up?

ANSWER Thermal switch is ground when cold. Since you are in Alaska, it's probably cold. I don't recall the exact temp but it's below about 50F. It will open above that.



--
3. So, I guess the question would be of the operation of the thermal switch. Does it show ground until activated, or should it only show ground when activated?

ANSWER Same as above.


4. What do I need to do to get the engine to idle a little more smooth and cut down on some of the idle hunt that is left? I have to say that the car now idles better than it ever has but it still runs a little rough. The whole reason I replaced all these items were to finally get rid of the rough / rich running. I know I'm on the right path, I'm just not completely there yet.

(Side note. I have not replaced the WUR, I just made sure the mesh filter was clear of anything that shouldn't be there prior to hooking up the SS lines).

QUESTION - have you tested fuel pressure at the WUR with a gauge? Hard to find otherwise. Typically a plugged WUR will cause a very lean condition.

.[/QUOTE]

[Horsebox]

Here's the video

http://youtu.be/qXqHotBThUM

Great work, you're nearly there. The lambda dwell, or duty cycle, fluctuating like that is normal if my engine is anything to go by. The system fluctuates between operating the engine very marginally too lean/too rich, according to the voltage from the lambda sensor. So the mixture ends up oscillating around its target point.

Your engine shouldn't stumble like that tho. I would agree with Dave to check the control pressure properly.

Although having said that, for the lambda to work correctly as it is doing for you now, there can't be much wrong with the fuelling. Did you check the injectors? Something there is giving you that lumpy idle.

[Horsebox]

You could also try clamping off the air hoses that go to the charcoal canister. I did that with mine, whilst plugged into an exhaust gas meter, and the results told the story of big air leaks from the canister or its pipe work.

[Trstno1]

Great work, you're nearly there. The lambda dwell, or duty cycle, fluctuating like that is normal if my engine is anything to go by. The system fluctuates between operating the engine very marginally too lean/too rich, according to the voltage from the lambda sensor. So the mixture ends up oscillating around its target point.

Your engine shouldn't stumble like that tho. I would agree with Dave to check the control pressure properly.

Although having said that, for the lambda to work correctly as it is doing for you now, there can't be much wrong with the fuelling. Did you check the injectors? Something there is giving you that lumpy idle.

The injectors were ok when checked, but I had a couple that didn't seem to have the best of patterns. I have since sent them into special T for cleaning. When doing the flow test upon getting them back they seemed nominal.

[Trstno1]

ANSWER Thermal switch is ground when cold. Since you are in Alaska, it's probably cold. I don't recall the exact temp but it's below about 50F. It will open above that.


ANSWER Same as above.

QUESTION - have you tested fuel pressure at the WUR with a gauge? Hard to find otherwise. Typically a plugged WUR will cause a very lean condition.

.[/QUOTE]

How exactly do I test for fuel pressure at the WUR? I imagine it includes purchasing a new tool...? Where do you hook it up and what are you looking for?

[Trstno1]

ANSWER Thermal switch is ground when cold. Since you are in Alaska, it's probably cold. I don't recall the exact temp but it's below about 50F. It will open above that.


ANSWER Same as above.

QUESTION - have you tested fuel pressure at the WUR with a gauge? Hard to find otherwise. Typically a plugged WUR will cause a very lean condition.

.[/QUOTE]

How long should the car warm up prior to the thermal switch switching from ground?