85 c4 flashing engine light/stumble
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
This whole problem is so intermittent that I seem to fix one thing and another pops up. Fix that one and the previous problem comes back. I know the connections at the computer are good, and I can't find any ground problems. Nothing changes when I move wires around or tap on the computer. Yet the interior light issue comes and goes as well as this check engine light/runs like crap issue.
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
No FSM, guess I'll have to go ahead and get one to better understand the wiring. Or go ahead and do the LS swap although that wasnt gonna happen for a few years. Maybe I need to look into a possible loss of power instead of the grounds.
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
Another thing I noticed: Fuel gauge doesn't work because the sending unit wiring rusted away (I verified this when I put the new fuel pump in). When I connect the ALDL pins A and B and the car won't go into diagnostic mode, the "range" gauge indicates 317 miles. When the car decided to go into diagnostic mode, the range went to 0, as it should. Does this mean I'm losing power or ground to the dash cluster, or is the range function go thru the computer? I already resoldered the PC board pins in the cluster according to batee's write up.
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
So last night I cleaned the 2 terminals at the back of the driver side cylinder head after verifying the ground on the same side of the block is good. That one only has the negative battery cable and ground strap back to frame and they are good too. After cleaning and reattaching the cylinder head ground, it ran fine. Went inside the house for a few hours, came back out, and now the check engine light doesn't come on, fasten seat belts light doesnt come on until I turn it on and off a few times, and the car won't run. It will however go into diagnostic mode if I connect pins A and B but the check engine light doesn't come on at all and doesn't flash. Going in circles here.
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
Today I checked for the ground under the a/c box, my car does not have it. I did notice that all the wiring for the starter was loose so I cleaned and tightened them. Then I clipped the ends of the 4 ground wires on the driver side harness, crimped new ring terminals and grounded them all together on the back of the head. Cut the end off the wires going to the oil pressure switch and crimped on new spades to make sure code 54 didn't come up. Which it did, the check engine light did flash momentarily, long enough for this code to appear. Reset the computer and check engine light doesn't come on at all again. All this wiring work did absolutely nothing to help. Tried grounding terminal A5 at the computer (removed) and check engine light does not come on. I know the bulb is good cause it was on a few days ago, and earlier today. Interior lights work, then they don't work. They always work if I turn them on manually so I know the ground is good. So it seems I am now looking for a bad positive connection. Time to tear into the dash
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
Forgot to mention: dash cluster was really bright, then it wasn't, now it is again and I have no clue on that. I've already repaired the broken solder joints so there's no reason it should be that way.
Racer
Joined: Jun 2001
Posts: 377
Likes: 10
From: Chicago IL
I had the same stumbling, surging and cut off issues with my 85 many many years ago. Thought it was burn off unit, maf, etc. I gave up and took it to the dealership. after their many failed attempts, they kept it for 4 days and isolated to a bad ecm. (I personally think they were just tossing parts at it until something worked. (I was not fun to have around on the showroom floor)
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Pro
Joined: Sep 2012
Posts: 732
Likes: 72
From: the confused state CT
It sounds like you have been over the grounds pretty good. A weak or bad connection on the positive side is another possibility. If you have any harness repairs that were done with scotch locks or crimp connectors I would check them and replace them, with a solder connection, they can be a source of high resistance even though they look clean. Then I would check the positive leads and fusible links for corrosion or bad connections, unfortunatly these problems can be a real pita to figure out. A fsm would be a great help with looking at the wiring diagrams and finding what the problem circuits may have in common. You'll get it, just keep at it.
Gary
Gary
Last edited by yd328; Feb 16, 2013 at 04:47 PM.
Le Mans Master
Joined: May 2006
Posts: 7,708
Likes: 266
From: indy indiana
sometimes alot of fixing a problem is finding out what ISNT wrong/bad.Its a pain in the butt way to go, but what can you do. I had your problems on a TBI unit,,was the throttle position sensor, no idea what yours is. best of luck.reading this with interest.
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
I did purchase a fsm and have been checking connections for a few days. Solved the problem of the brake light always on (emergency brake switch) and courtesy lights (bad solder joint on dimmer module). Last night it wouldnt even start, wasn't getting pulse at the injectors and kept spitting out code 54. I unhooked the 4 wire dist harness and applied reference pulse to computer, got nothing. So I did a warranty exchange on the computer just to eliminate the possibility of a bad ecm. But before I did that I check all power to ecm, all good there except the check engine light stopped working again. I'm wondering if the loss of power to the check engine light is indicative of the problem, in other words, a positive issue instead of ground issue. I will try to hook up the new ecm and see if it runs but i'm afraid it will get fried by whatever this problem is.
Pro
Joined: Sep 2012
Posts: 732
Likes: 72
From: the confused state CT
Check the power feeds to the computer, if I remember correctly there is a positive right off the battery for ecm power. Check the fsm for that and any other power feeds (+). I've seen these problems at times, especially when someone adds an alarm, remote starter or stereo equipement. The power feeds get tapped into and the problem occurs where they splice into the wires for the accessories.
Gary
Gary
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
There is one ground I haven't been able to locate, the one that is supposedly to the left of the column. Do I need to take the cluster back out to see it? I'll probably take the dashboard back out anyway to get to the main harness.
I do appreciate everyone's input on this. I've mostly stuck with older cars, mainly Trans Ams, and have never had a problem like this. Of course those cars are much simpler and not fuel injected.
I do appreciate everyone's input on this. I've mostly stuck with older cars, mainly Trans Ams, and have never had a problem like this. Of course those cars are much simpler and not fuel injected.
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
Well after checking the wiring harness one more time, I decided to install the exchanged ecm. And wouldn't ya know it...fired right up. Ran perfect as I put all the dash back together, bolted the computer back in, and all the trim. Tried it again after a few hours and not one hiccup. Tried it again today after work and ran perfect even in this cold weather here in Cincy. I'm reluctant to say it was a bad reman ecm I got initially, but it appears that is the case. At least, like ghoastrider1 said, I now know what ISN'T wrong with it. Plus I have the wiring diagrams memorized lol. I hope to say this thread is closed. Again, thank you all for your contributions! Gonna put some miles on the new BFG Sport Comps this week and weekend and see how she does.
Thread Starter
Racer
Joined: Jan 2013
Posts: 403
Likes: 87
From: Cincinnati OH
Ok, back again after 5 months of reliable driving. Coming home from work today, I was toying around on the highway and noticed when I hammered it, it stumbled and stuttered badly and didn't pick up speed, yet when I let off, it ran fine. In fact it runs perfect as long as it is at half pedal or less. There is a point in the throttle where if I go past about half, it starts to stutter and run like crap. I checked voltage at the TPS and it measures .5 at idle and 4.95 at full throttle. It idles perfectly around 600 and runs strong until I go past half throttle. Any suggestions?? I'm glad I didn't embarrass myself in front of that damn Miata