Hello, i picked up a sanitary 1990 c4 a few weeks ago. All in all its a very nice car and almost everything works and when it runs right it runs goooood but i get an intermitten ses light it flashes and causes a rough idle. In the worst cases it will stall it, in the best i just lose a lot of power. I also have a sys light in the digital display and 99% of the time i lose my speedometer and instant mpg. It seems like a few bad grounds to me? Any input or similar experiences? It wont give me any codes from the self diagnostic, i can only get a code 12 for no dist. Signal which goes without saying. I sent a can of sea foam through it and it ran GREAT but come the next day it ran like ****. Any input is greatly appreciated as i plan to soon sell every car i own and go buy a sanitary c6. Thanks in advance!

 

If the injectors are original & it runs ok when the engine is cold then bad when it heats up I would start with checking the injector ohms cold vs hot.

If the injectors ohm out ok suggest changing the ignition control module in the dist its another heat related item.

Good luck.

 

Code 12 = "no problems found" (that's good).

I'm betting on loose wiring, or ground problem, as you suggest.

 

Hey thanks for the quick replies, i'll check the injectors next chance i get. Is there a diagram highlighting all of the ground points on the car? Im new to corvettes and so far its been an absolute night mare trying to locate these wires.

 

Grounds for an '86.... probably similar on all C4 years (compliments of Cliff Harris:
http://home.earthlink.net/~cliff_har...s/grounds.html

 

Well i've cleaned the main grounds and took particular care with the g104 with no results, it runs every bit as bad if not worse. Havent checked the injectors yet, it doesnt seem to be in any way related to heat though it does it at any given point in time.

 

Could it be as simple as a gummed up injector? The car sat for many years under a tree. I ran a can of sea foam through it the other day and it ran GREAT immediately after then the next day it ran terrible again. Should i run another can of sea foam through it? Last time i pulled the brake booster vac line loose and dumped the can in.

 

Are you downloading the DTCs correctly?

http://tech.corvettecentral.com/2011...trouble-codes/

 

I believe i am, i will try again today though. Its starting to pop and back fire a lot more now, it sounds like its running real lean on cylinder 2 or 4 which kinda makes me wonder if i do have injector issues?

 

I was thinking you were running lean from the first second I read your original post. When you check your codes, it will flash code 12 3 times before it displays the actual fault codes. After those 3 times, it will start flashing the codes.

 

Don't know if the following comments will help..... from another forum:

Injectors/Code 45
I have read with great interest about the various problems with Multec fuel injectors and have discovered that this most likely the cause of the Code 45-rich exhaust on my 90 L98.

I measured the resistance of the injector on cyl 4 and it was about 5 ohms the rest were about 16 ohms. I used a scan tool to watch the O2 voltage and integrator values at idle and noted that the O2 voltage was steady at about 800mV and the integrator was 80 both indicating a rich condition. With the injector wire to cly 4 disconnected the O2 voltage fluctated as it should and the integrator climbed to 112 (not perfect but much better). It's seems hard to believe but with the injector wire disconnected the engine actually runs a little smoother at idle and the vacuum reading is a little higher.

I am going to replace the faulty injector and have noted that there are several options like Ford/Bosch pink tops ....however I would like to keep the car as original as possible and keep my costs down.

Response:

Soon after I bought my 90 I noticed and irregular idle that would come and go .After awhile I notice that it would idle better when cold which is when the ecm calls for more fuel. Last summer I check the ohm readings and found one at 7 and another at 9. They are the OEM injectors.When I replaced my intake gasket for oil leak reasons I replace those two injectors and it solved that problem. The strange thing is I didn't get any codes.

 

Well i managed to get a c41 a h41 and a --- out of module 1. From the ccm, it then displays module 4 as err and it says 1.0 but doesnt display any further info. Anyone know what those codes mean? I can still only seem to get a 12 from the ecm.

 

From the link is sent you; http://tech.corvettecentral.com/2011...trouble-codes/

Code 41: Loss of ECM serial data communications

 

So that means theres a bad connection somewhere? Haha how am i supposed to pin point that connection? I dont even know where to start.

 

Oh and i ran an ohms test on all 8 injectors they all consistently read 17 cold and hot

 

So i've been pacing around the car and decided to try wigglimg some of the wires going to the ecm, i wiggled a couple and heard what sounded like a relay click on the pass side of the compartment. I climbed in hit the key and boom ran great, so im assuming thats the problem. Im gonna drive it to down to verify. If it is the problem what can i do to ensure a good connection? I've already thoroughly cleaned all plugs with electrical cleaner, what now? Lots of di electric grease?

 

From another site: http://corvettephotographs.com/c4vettes/ecm.htm

scroll down to code 41: check wiring at ECM. Possible PROM failure, or incorrectly seated PROM. Reseat PROM. Possible ECM failure.

When I have time, I will research my FSM for additional suggestions.

You can try searching google..... many searches will direct you to
the Corvette Forum.

 

Im pretty confident at this point its a bad connection, any time it runs bad i wiggle the wiring real good and it picks up.

 

From my post #3......"I'm betting on loose wiring, or ground problem, as you suggest."

Now, trace that wire, if you can......problem solved.

 

Haha right and i never doubted you, i cant seem to pin point which wires are loose, though i think i know which plug it is thats causing problems.