CHT Sensor Ohm Measurement and Pic

Talewinds · Talewinds's Garage

I'm really getting serious about diagnosing my cold start issue in my 88'. One of my few demands from a car is that when I turn the key I want it to fire on the first attempted start and stay running with confidence, pet peeve I guess . My problem is a seemingly common one with the 3.2 Motronics, I turn the key, it fires then dies. Turn the key again, it fires, then dies. After 3 or 4 attempts like this I get frustrated and use the gas pedal to keep it running after it turns over on the next start. After I get it to stay running the idle of course bounces between 400-1800 for several (20) seconds and THEN appears to operate as it should, which means a higher steady idle at 1200 and then slowly declines to 900 and has a nice steady idle. After reading innumerable posts here about the issue, I'm still yet to determine if anyone has ACTUALLY cured this problem or just thrown parts and time at it then given up and lived with it!?!?!?
This morning I measured the resistance on my CHT sensor (I think?). Ambient air was 53* and the car was overnight cold. It measured 1000 Ohms. This appears to be out of spec as cold is supposed to be 3000????

stlrj · 03-15-2009, 08:39 AM

Oops, looks like you're measuring the resistance for the circuit board inside the DME.

Now, try placing your probes on the engine side top connector which you should now be seeing about 3.5K.

Cheers,

Joe

Talewinds · Talewinds's Garage

Ya, uhhh, just seeing if anyone was paying attention!?!?
Crap, and I wondered why the wire appeared to head straight toward the firewall and not towards the engine... So just fyi to everyone, the DME side of the connector reads 1k Ohms.
Hmm, so reading the correct side I got 3.45k. Perfectly within spec.
Thanks for the guidance Joe.
Bummer, I kinda hoped the CHT would be shot, seems like a relatively cheap and simple fix.

stlrj · 03-15-2009, 12:13 PM

Had a feeling all was well in the CHT dept. That's too easy.

You might check for vacuum leaks at the base of your intakes. Spray some carb cleaner in that area at idle and see if anything happens.

Just a hunch.

Joe

Nine9six · Nine9six's Garage

Also check ICV and O2 sensor

Talewinds · Talewinds's Garage

I bought some starting fluid today to try the intake leak possibility, I'll try that this week.
I had previously removed and tested the operation of the ICV with a battery and also Ohm'd the terminals on the ICV, all checked out ok there.
Although the car runs well at higher RPM, I'm wondering if it might be running rich, seems boggy/ sluggish anywhere below 2000rpm. O2 sensor might contribute to that also???