3.2 cold start issues

[steely]

I've been having classic cold start issues with the seasonal drop in temperatures here in SE Pennsylvania the past few weeks. So I read a lot of the existing threads and tried a few tests. While I did not complete everything, and while I hope not to get ahead of myself, I was wondering about the DME side of the idle compensator / control valve (ICV).

Lotta threads on the subject, but not many with how they wound up solving it. Hopefully you guys can provide me some clues.

Otherwise fine running 87 displays hard starting in cooler than normal temps (<50F). Easy start, no hunting idle, just nose dives to stall. Runs fine if I keep throttle at ~1-2K rpm for half a minute or so.

Car runs great when warmed so I don't suspect plugs, wires, cap, rotor, fuel filter (all new last year), or fuel pressure.
I don't suspect an air leak mainly because I got a pop when I pulled the vac line under the boot to the brake booster 2 hrs after she was parked.

Throttle Body idle switch reads ok (0 ohms/closed at idle, infinite when off idle)
CHT read 3.44Kohm @ ~50F
AFM IAT - 3.46Kohm @ same temp - did not test wiper resistance.
AFM +5V - not tested
O2 sensor - not tested

ICV - No vibration - just a electric hum (screwdriver stethoscope).
Read 40 ohms across outer 2 pins and 20 ohms from each outer pin to the center pin - so I suspected dirt, but I removed and it looked clean, so I did the 9V battery test and it opened and closed alright.

I did measure +12V at the center pin of the harness connector to gnd (key on).

Could this be a DME issue and is there a way to test it w/o a scope?
DME cold solder joint inspection warranted or am I barking up the wrong tree?
Should the ICV vibration be easy to feel?
Could my idle be fubared to begin with.

sorry for the long post - Thanks for any ideas/help guys.

[bkreigsr]

to direct you down another path - have you inspected all the vacuum lines? - edit; not sure if the brake booster is a valid test for the entire intake system.
I pulled my useless cruise control servo last Sat and in the process, found 3 severed/cracked vacuum hoses & repaired. Now - no more symptoms (exactly like you described). - all better.
(on my recently acquired 85 3.2)
Bill K

[steely]

Thanks Bill -

I thought it would be a good test of the vacuum, unless there is a check valve in the line closer to the engine. It was actually mentioned in at least one thread as method for testing for system leak and the line off the engine near the transmission that is prone to get ignored. I had replaced the pipeline and 1 or 2 smaller lines 2 years ago to when I did the fuel lines, but I'll double check as I am now not sure if I did the ones to the TB or not (Y between the PR and damper?)

Was hoping to get a response to the "how much does the ICV vibrate" question.
Am hoping to borrow a scope to check the ICV signal (gnds) from the DME.

[steely]

I confirmed that I only have one side driving the ICV, but that could be because it is cold.
Would anyone here know if the PWM drive duty cycle on one side is ever completely zero on one side? I would have expected near zero, but not nothing.

[steely]

A couple of pics.

Scoped both sides of the ICV drive - the pic below shows a good signal although it's tough to make out. There was no signal at all on the other side (no pic of it).



The 2nd pic shows a burned ICV trace (to pin 33). The in -circuit transistor readings are goofy too.



I'll try to score some, clean things up and jumper the trace. Won't be the weekend I'm afraid.

credit to landwerlen for his early thread.
Thanks CW for the scope!

[DRACO A5OG]

Oh Man, Please update details!

You sky rocketed over my head

Which half was that burnt out solder?

[stlrj]

Originally Posted by steely

Lotta threads on the subject, but not many with how they wound up solving it. Hopefully you guys can provide me some clues.

Otherwise fine running 87 displays hard starting in cooler than normal temps (<50F). Easy start, no hunting idle, just nose dives to stall. Runs fine if I keep throttle at ~1-2K rpm for half a minute or so.

Have you tried raising your base idle speed?



Cheers,
Joe

[DRACO A5OG]

Oh, he found the culprit in the DME itself.

[steely]

It's been awhile - I will try not to ramble.
In researching this back in Nov last year, and once I had a diagnosis (no return path for one side), I found John Landwerlans' thread - a major help:

motronic idle surge solution

John had a scope, I didn't. Bentley says to check the +12 and I could do that with my crummy meter. I could also check the icv winding resistances noted above (ok) - but the +12v is just power, and the DME folks switch the icv sides by using 1 transistor for each of the 2 sides. The DME doesn't 'send a signal, rather it provides a path of the +12v back to ground thru the transistors. If one gets pulsed more that the other, you steer the icv open or closed like a servo. (moral: the 2 things bentley said to check were ok)

The transistor(s) apparently can overheat - not sure if age, workmanship, part fatigue, or (gulp) design contribute.

When the transistor goes, it could burn out a trace, and might hurt the icv too before it dies.
I didn't have my own scope at first, so I simulated the winding resistance with a resistor (100ohm?) and I put an LED in the path. I did this for each leg. If the dme (this section) was ok, both leds would light, but one did not. I later borrowed a little scope and confirmed no squarewave drive signal.

Then I removed and inspected the DME and found a smoked trace under the one drive transistor. I cleaned it all up (alcohol - not the best thing actually), removed a bad piece of trace that could cause a short, jumpered the trace with 22 awg wire, and replaced the transistors (pair) with some BDX53s (mouser PN 512-BDX53ATU) (64 cents/ea).

[DRACO A5OG]

Damn it Dan, Just Ramble, It will be our problem if we can't keep up.

I have engineer's talk to me infrequently and my eye's glaze over all the time . "Damn it Jim, I'm a Salesman not an Engineer" (play on Star Trek)

Originally Posted by steely

It's been awhile - I will try not to ramble.
In researching this back in Nov last year, and once I had a diagnosis (no return path for one side), I found John Landwerlans' thread - a major help:

motronic idle surge solution

John had a scope, I didn't. Bentley says to check the +12 and could do that with my crummy meter. I could also check the icv winding resistances noted above - but the +12v is just power, and the DME folks switch the icv sides by using 1 transistor for each of the 2 sides. The DME doesn't 'send a signal, rather it provides a path of the +12v back to ground thru the transistors. If one gets pulsed more that the other, you steer the icv open or closed like a servo.

The transistor(s) apparently can overheat - not sure if age, workmanship, part fatigue, or (gulp) design contribute.

When the transistor goes, it could burn out a trace, and might hurt the icv too before it dies.
I didn't have my own scope at first, so I simulated the winding resistance with a resistor (100ohm?) and I put an LED in the path. I did this for each leg. If the dme (this section) was ok, both leds would light, but one did not. I later borrowed a little scope and confirmed no squarewave drive signal.

Then I removed and inspected the DME and found a smoked trace under the one drive transistor. I cleaned it all up (alcohol - not the best thing actually), removed a bad piece of trace that could cause a short, jumpered the trace with 22 awg wire, and replaced the transistors (pair) with some BDX53s (mouser PN 512-BDX53ATU) (64 cents/ea).

[DRACO A5OG]

Oh Fudge, GENIOUS! Will take a look at my DME halves.

[steely]

some pics:
The component side of the board with the bad trace. Bad trace was under black transistor (also bad) at 9 o'clock.


transistor removed (now at 12 o'clock in pic)



I actually removed both transistors and replaced them here using nylon screws.




reverse side - cleaned up/removed scorched trace, you can see unsoldered transistor pins at this point.

[steely]

cut down nylon screws, soldered jumper in place.



tested after assy in car w/o connecting to ICV at first. Both leds lit up.
Thank you John L where ever you are.



At this point I only have ~1000 miles on them.

HTH and cheers.

[steely]

Originally Posted by DRACO A5OG

Damn it Dan, Just Ramble,

LOL

Originally Posted by DRACO A5OG

I have engineer's talk to me infrequently and my eye's glaze over all the time.

I get the same reaction from my poor wife :-)

[DRACO A5OG]

Originally Posted by steely

I assume the brownish colored one is the old one, Yes?

[DRACO A5OG]

Originally Posted by steely

I get the same reaction from my poor wife :-)

Well, I'm in good company , Just don't call me Shirley (pronounced Surely)

[steely]

Originally Posted by DRACO A5OG

I assume the brownish colored one is the old one, Yes?

Yessir. (ON EDIT - see next post below)
If you look at the very first pic with the red circle from last november? it is scorched.

I cleaned the off the carbon, and 'wicked' away the blob, and discovered that the heat thru that thin trace made it delaminate (word?) off of the board, so I cut it off. The brown is like stained printed circuit board w/no good trace, so I added the white wire.

I have some back ground, but while I was doing this I kept wondering if I was doing more damage than good. I can direct folks at work to do this on products, but it felt different when I would realize it was my own car.

[steely]

Originally Posted by DRACO A5OG

I assume the brownish colored one is the old one, Yes?

NO I AM WRONG - I mistakenly thought you were referring to the other side of the board. (different pic)

The Brown one is GOOD if I understand you. The bottom one has some incandescent light bouncing off of it and it just looks brown. The top transistor died. I replaced the PAIR. There was no external evidence of damage on the transistors themselves. The top one did measure bad. I figured the other was stressed and replaced it. The brown looking one is now good.

[DRACO A5OG]

Oh I thought that was the case, damn lighting

So was there any exterior defects, like melting on the top transistor?

The jumpered joints was it the "R409" component, gray barrel looking thing?

Sorry, I am a closet engineer I use big words like "thing" whatchama call it, etc..."

[DRACO A5OG]

Originally Posted by steely

I have some back ground, but while I was doing this I kept wondering if I was doing more damage than good. I can direct folks at work to do this on products, but it felt different when I would realize it was my own car.

Yeah, but they can't BS you now