I thought this board would be the best place for this question. I’m trying to track down a hard start/idle problem and was trying to use my autoxray (laptop is down) to track it down and was having trouble getting it to link. Well the ALDL was pretty corroded so I replaced it and was still having an intermittent problem with the autoxray linking. So I checked the grounds at the computer (A12,D1,D3,D6,D10) and all 5 measure 5.5ohms to ground under the dash. Higher then I would expect but still vary low. I tried jumping the pins at the ALDL and the SES light was flashing 12 so it seems the connection from the ALDL is good. So swap out the computer and the same problem. So now I’m having a hard time finding the first problem, hard start/hunting idle. It’s making it hard to tell if it’s mechanical problem or tune, and then track it down.

So my questions are:
1. Should I be seeing less then 5 ohms at ground on the computer harness?
2. Are all the grounds in the computer tied together, so taking one straight to ground would pull them all down.

 

The answer to both your questions is yes. You should actually be seeing less than .2-.3 ohms and preferably down to .1 ohm to ground. Anything more than that is not grounded. I also had a hunting idle problem on a 90 RS with MPI. It turned out to be an idle adjustment that "wasn't supposed to need adjusting." Exact same symptoms: hard to start, idle fluctuated but ran fine going down the road. Not sure it'll help, but good luck.

 

Question number 2 was the big one. Was planing to running a good ground strap to something under the dash but needed to know if I had to run 5 of them or just the one. I’ll try that this evening.

 

One ground should be fine. I recommend grounding one and checking the rest. If they are less than .2 ohms, great, if not ground the rest also.

 

Do you know off the top of you head if the case is grounded. It would be so simple if I had a Schematic for the computer and not one of those half a$$ block diagrams.

 

I just went and checked mine. .3 ohms from the case to ground. If it's more than that, try running a jumper from the case to a ground and see if that fixes your problem.

 

hmm i had a hunting problem sounded just like this ended up being the egr sylenoid was wired to the wrong point. ran real odd. but that was during an engine install.