qwiketz

hi guys. I was able to borrow a copy of the factory service manual. When pulling codes, I got code 41.

The car has fuel pressure (gauge on rail) but doesn't start. This error causes the injectors not to fire. I have not confirmed if there is or isn't spark. I am not getting any other error codes. I am also getting the fans on the engine cooling system going on as soon as the ignition is turned onto the accessory position. I am able to scroll through the codes so the buttons for the instant data stuff are working.

I have taken the interior of the car apart and unhooked the ccm. I have also unhooked the ecm in the engine compartment.

I bought a tool from harbor freight to test the continuity of the circuit. Basically you hook it up to a wire and there is a wand that makes a sound as you trace the wire. If it has breaks, the sound volume goes down.

I hooked it up to aldl position M which appears to be connected to both the the serial data lines. I then followed the lines with the wand to the ecm and then tested that the signal was getting to the ecm in the engine compartment. It seemed to work and it appears that there are 2 tan lines going into the ccm on the teal colored connector and 2 going to the ecm on the red connector.

So basically, if I have good continuity on the serial data lines, would that indicate that it's a ground issue as long as both the ecm and ccm were getting power?

I understand that the data has to go from the ccm to the ecm, but I don't understand test 4 and 5 in the factory service manual. It seems like test 2 & 3 are testing between the ecm and the ccm but then it goes to ground in test 4 and then it calls for using a test light in test 5. Test 5 seems to test whether the unit is getting power to send the signal and is sending the signal but I still don't understand test 4.

Electrical diagnosis isn't exactly my forte. I would send the car to the shop but it is all taken apart and doesn't run so I'd have to have it towed to the shop.

Anyhow, any advice or guidance would be awesome. I feel like I'm somewhat close, but then again the car has been down for what seems like at least a year!

Finally, if it is a ground issue, should I try to cleanup the grounds on this car? I swapped out the trans twice in the past few years and perhaps the grounds got dirty/oily. Also, is there a certain way that I should be separating the 0-ring connectors on the ground so that they have the best conductivity?

I've attached the scanned copies of some of the fsm. Thanks in advance!

9T3VETTE

You are correct that there are 2 tan serial data link wires running between the ECM and CCM.

Steps 2 and 3:

Checking for continuity in one of the serial data lines --> two different pins in the CCM connector. If continuity is not present, there is a break in the wire somewhere. You'll have to trace and fix.

Step 4:

Checking for continuity between CCM WC13 and ground. So take your multimeter and stick one end in WC13 and the other end to any known good ground on the car** (they are all tied back to the same ground loop). If continuity is present you have a short in the wire somewhere to ground. You'll have to trace back and fix.

**You can verify a good ground by checking continuity between the suspected ground and the battery negative cable. If there is continuity, you've found a good ground.

Step 5:

Is checking for a short to battery voltage. If you connect a test light between terminal WC13 and ground and the bulb lights up, there is battery voltage getting to the serial data line somewhere.

You can also use a multimeter instead of a test light and check for voltage present from WC13 to ground.

Step 6:

Repeat the above using the other serial data line

qwiketz

so I'm looking at charts for the ccm 8d10-8d13. There is 4 charts yet the ccm has 2 harnesses that go into it, one grey and the other mint colored. I paged through the manual and I'm not seeing an easy way to match up the chart 8d13 which has the 2 tan serial data wires and the harness. More specifically, I guess I could go off color, but there isn't a shot of the plug side of the harness so that I can easily tell what position to stick the multi meter into.

I'm using a 1990 manual. Did the ccm change from the l98 years to the lt1 years?

WVZR-1

You need the correct year FSM for sure, the CCM changed dramatically from '90 to the years that followed. DAB was added in '91 and later years. Each year has potential differences. There's certainly similarities but NOT similar enough to try substituting an incorrect for diagnostics.

You've confused me, in your other thread you mention ordering a FSM but waiting (early Oct), "Seabright" I believe offered up '92 scans from the FSM. What all do you actually have? Are your attachments from a '90 or '92 FSM?

qwiketz

Hey WVZR-1,

I did end up getting the c41 trouble shooting diagrams from Seabright. I just emailed him again to see if he could possibly forward the ccm harness diagram and the ecm harness diagram.

I originally ordered a fsm back in late October but I never ended up seeing it and got refunded my money. I did borrow a 90 fsm off a local member. I did re-order the 1992 corvette service manual and I did order book 2 for the electrical diagrams. They will be here sometime next week. I thought I could get by with the 90 but I cannot.

Hopefully, I'll have more info soon which will help everything make much more sense!

Cliff Harris

I recall a LONG thread of this subject a few years ago. It got very detailed into exactly what was happening and why it failed. I didn't bookmark the thread and a quick search turned up nothing useful, so...

I suggest Googllng "site:corvetteforum.com serial data loss of communication".

WVZR-1

For the he!! of it I'd add the year desired

"site:corvetteforum.com serial data loss of communication 1992"

I believe one of the more simple solutions years ago was replacement of the "cluster" fuse. I believe the CCM relies on multiple fuses and it's very easily overlooked. The '92 FSM should certainly help.

Have you replaced the ECM at some point? Have you considered the possibility that the ECM could actually be the issue. Maybe try and borrow a known good ECM?

9T3VETTE

Agreed. If the serial data line wiring checks out it's more than likely an ECM issue.

qwiketz

Hi Cliff,

I spent quite a few weeks researching this problem in reading some of the threads that were online . I saw a few good ones over a Corvette action center.

One of the main reasons I'm trying to diagnose this problem as thoroughly as possible is because several people went through quite a few ECM's 'S in the process of trying to fix their code 41 . Since I have a 1992, getting a replacement ECM is almost nonexistent. So I would have to send out my current ECM to be rebuilt . I did see a thread recently talking about companies that build the ECM's . I want to say it was $45 to test it and about 180 to rebuild it . I would be perfectly OK paying the 180 if I knew that that would fix the car . So, little by little, I'm trying to narrow down the potential problem .

Some of the other fixes to the problems that I've seen have been ignition control module's, coil and ecm. I don't recall seeing one ever being this ccm. I have also heard of people having having a bad splice in the tan wiring between the ECM and the CCM .

qwiketz

I believe one of the more simple solutions years ago was replacement of the "cluster" fuse. I believe the CCM relies on multiple fuses and it's very easily overlooked. The '92 FSM should certainly help.
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I did see a thread where the cluster fuse caused a problem. That was one of the first things I checked since it was so simple . I put a test flight to several of the fuses to verify that they were OK .

rsc337

Hi Qwiketz, I have a 92 Service manual, both books if you want to look at it just pm me. I live in Costa Mesa. Are you still selling your car?

qwiketz

Thanks for the offer. Mine should be here sometime this week or early next week; it's hard to tell with the holiday. Supposedly they went out Friday.

I was looking to sell the corvette to buy a cts-v but the wife ended up getting a different car to replace our volt being returned on lease. So, I'm now determined to get the car running and I'd really like to take it to the track at least once.

I take it you have a 92. Any issues with your ecm over the years? I am starting to get to know a few local guys that work on their c4's. Hopefully we can cruise out and grab lunch as a group and talk cars which would mean I've fixed this problem!

rsc337

Hey qwiketz, I look forward to you getting your car running because I know it's fast! I was thinking about buying your motor when I saw it for sale, but I'm in the middle of building a 1959 El Camino right now. I've had no problems with my Ecm/Opti as of yet.
When you get it running just let me know.

qwiketz

hi guys. I have the manuals on disc now if anyone needs any info. I've yet to do further testing with the pins due to work, but I did send out the ecm to sia today to be tested. I'm about to leave on a cruise for a few days so I was happy to get it out on the last day I'm around. Hopefully they'll find something but with my luck, they will find something and it sill won't run!

Well, hopefully not. After cars and coffee last weekend, I'm salivating to impress people with my car that sounds wounded yet will smoke their super cars from a dig or roll!

1993C4LT1

Best of luck

qwiketz

just spoke to SIA about my ecu. They said that it had bad solder joints throughout, so they repaired that. It is now in transit from back east out here to CA. Hopefully this does it but we'll see. Nothing is ever easy!

0BDE-Systems

Beautiful car - I'm up the 101 and was oh so very tempted by your for sale ad. I hope this fixes the car

qwiketz

If I get it going I'll let you guys know. Perhaps we can setup a cruise event with some of the so cal guys on the forum. I've actually had several local guys reach out trying to help get the car back on the road.

rsc337

Hi, Did you get your new ECM in the car yet? I'm looking forward to this car running again.

qwiketz

hi guys. I got the ecm and ccm hooked back up in the car. The c41 is now gone. However, I'm getting a h54 error on the ccm section and I'm getting "errr" on the ecm. I'm not getting any ecm codes though.

I tried starting the car and I'm not getting any spark at the coil. I do have fuel pressure and 12v on both of the injector terminals.

I did have to reinstall the moates adapter into the ecm. I double checked that it was seated properly but it looks okay. I'm going to next try to to double check the prom to make sure that it matches up with my file.

Any other suggestions? I do have the factory service manual, but I didn't see any discussion of the "errr" message.