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Yup ,Reduced engine power again- such a worn out topic

Delta98C5

Member
Joined
Oct 4, 2019
Messages
20
Location
Jefferson Parish, LA
Corvette
stock 98 C5 pewter 145K miles
I've decided to delete this post. There is no delete option so I had to do this . I'm selling the car to a race car driver who is going to strip it .
 
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gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,521
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Whats wrong?
You giving up?
grounds,Grounds,GROUNDS High resistance or non existent grounds make electronics do weird sh*t !~~!

Pull the codes and tell me what you got.History and Current
I used'ta be a Corvette technician,Now I'm just a beekeeper.

https://www.corvetteactioncenter.com/forums/c5-technical-and-performance/72535-pulling-codes-c5.html
 
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Delta98C5

Member
Joined
Oct 4, 2019
Messages
20
Location
Jefferson Parish, LA
Corvette
stock 98 C5 pewter 145K miles
I was giving up last night . It's not the car and these issues bugging me which really haven't been many . The horns and the wipers have been far more annoying but shutting down on the interstate at 70 mph has me reevaluating keeping the car. Also the fact that the TAC modules seem to be rare and putting a used one is as much of a gamble as I see it . I have to say I feel at this time that GM is responsible for not continuing to make at least the electronics available. 50 years from now how many C5's are even going to be on the road if no modules are available and no one is repairing them? It will take someone either repairing the modules themselves or rewiring the car to run without computers. Keeping a car like this on the road will be nothing like the older Corvettes . It still love the car and had been thinking of finding an 03 or 04 but then I'd be back in the same boat wondering when the demon would come to the surface again. I removed my original post because I thought probably this is such a worn topic no on would reply and I emailed the guy wanting it . Today the code is gone and I drove it up to the parts store to let them put their cheesy tester on it . I was hoping the alternator or battery was going to show something but nothing turned up . I have contacted the New Orleans Corvette club and they gave me a guy's number at Clearview Auto who has answered my email earlier today. I am aware of the ground issues . A while back I did pull the plug on the TAC and inspect it when I swapped the battery . It was clean and dry but I know that it could still be the problem. I had the P 1518 H code as well as the C 1278. When I was stranded the 1518 would not clear but this morning it did and it ran normally which is baffling to me . I guess this supports your statement on grounds. Thank you for your input and advice ! I used to live in Asheville and remember Old Fort.
 

gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,521
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
I rarely find any modules defective, It is usally a corroded pin on a plug or high resistance ground. Just because you get a code,Don't mean you have a defective part. The code just gives you a place to start looking.
You had a P1518 "PCM to TAC module serial data circuit" primary code, The C1278 was caused by the PCM temporarily inhibiting the TCS.
Normally by the time I get C5 in with codes they have 10-12 hard codes and are running like a 3 legged dog because the owner has just kept on driving and didn't have it checked out sooner. So I start by cleaning ALL grounds,Clearing the codes and go for a drive,Sometimes it can take 2 blocks or 50 miles before it sets a code,or on some sometimes they never reset one and are good to go.

On yours I would at least disassemble, clean and inspect grounds 9,8,7 and 6. Remove from the ground lug,take apart the splice pack 8 and 7,They can sometimes be really nasty.

[FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]https://www.corvetteactioncenter.com/forums/attachment.php?attachmentid=20400&d=1339434059

[/FONT][FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]https://www.corvetteactioncenter.com/forums/attachment.php?attachmentid=4328&d=1309856961

Now for checking the PCM and TAC module plugs for corrosion you'll need to get the car up so you can get to them from behind the rear rt. front wheel well lower splash panel. The PCM is mounted to the frame and TAC module is mounted above it on the fiberglass inner structure.

Hope this helps,If you don't find any green pins let me know,I'll fire up the old Dell with the GM service program and go from there.:thumb

PS In case your interested ,My C5 has 139,920 miles and has been the most trouble free and lowest [FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]maintenance[/FONT] Corvette I've ever owned.:lou:lou:D

[/FONT]<strike></strike>
 

Delta98C5

Member
Joined
Oct 4, 2019
Messages
20
Location
Jefferson Parish, LA
Corvette
stock 98 C5 pewter 145K miles
Thanks for the links. I will tell you I looked for those two splice packs under the hood , one left and one right and near the forward end of the engine compartment back in the summer the last time this happened. They were gone . I'm guessing they were removed by the last owner who put the NCRA stickers on my car. In their places the wires look to have been professionally repaired with round metal straps (probably the wrong name for them) and they're attached to what appear to be copper or brass studs. I'll have to get some pictures and show you . As an FYI my car is considered rebuilt. A mechanic I knew when I got the car put it on his rack and said the frame and everything else overall looked good for a car it's age. I know I've been putting off getting into the grounds. Today I checked the codes and there was one I'd never seen before P 0705. Thanks for your help!!
 
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Delta98C5

Member
Joined
Oct 4, 2019
Messages
20
Location
Jefferson Parish, LA
Corvette
stock 98 C5 pewter 145K miles
The latest on my adventures with Farrah (my 98 :L ) . I decided to access the PCM TAC area again after I had cleaned the four grounds in the engine compartment which really didn't look bad . I pulled the plugs out to inspect them and the pins and plugs looked really clean but the outside of the PCM looked like it was something out of the petrified forest so I removed them both , wire wheeled the outside of the PCM and painted it with krylon primer/ spray paint white and it looks pretty good . I bought contact cleaner spray and sprayed pins and plugs and blew them out with some air . My horn had been offline and I had the membrane sitting here so I pulled that out , installed it and set it aside . The battery was still disconnected and the number 16 fuse inside the car removed .I already had removed t he knee panel and the pieces surrounding the column so I decided to remove the wiper stalk and I took the little cover off of it to see what was up and it looked really clean inside . I guess the problem is in the washer button area but the little contacts both look really clean but I know I'm guessing . I still don't understand this issue. I"m wondering if there is anyway to clean those little points with a file or something . I know when you press the button it forces both of those open and the washer cycle starts . Is it possible they just aren't making good contact? Today I finally reinstalled the airbag horn assembly and tightened it down . I hooked up the battery and the car started no problem and no airbag light but the horn won't work and the wipers came on and were stuck so I cycled the handle and button and they went off for now . I turned off the engine and tried the horn again and nothing. I set the alarm and horns bonked so now I have to figure this out again . The membrane I got from Contemporary Corvette in PA had a different ground plug so I had to cut the eyelet type off of the old one and twist the wires together and tape . I made sure to twist them together very firmly and tape well so I don't think that could be the problem . I've been on a bad run of luck with the car as the left headlight motor gear decided to go out too . I removed it and took the cover off and the gear itself was not stripped . The rubber insert inside of the gear was torn to shreds and this caused the center eyehole of the gear to fracture. I found a guy on ebay , Carguy8t8 who charged $115 with shipping to rebuild the motor with a new aluminum gear and paint it too . He had really quick turn around and it works fine . I"m thinking this is a good deal versus buying the gear and just replacing it yourself but y'all can check it out for yourselves .
 

Catman63

Member
Joined
Jan 13, 2020
Messages
8
Location
Gering Nebraska
Corvette
2006 machine silver convertible
Check the connection on the TAC module for moisture. I had a 2001 that I fought this problem for along time. The root cause was moisture in the wiring connector behind the right front inner fender. replaced the connector seal put some dielectric grease on the seal and sealed the back of the connector with some silicone. never had an issue again. take a look its worth a shot.
 

Delta98C5

Member
Joined
Oct 4, 2019
Messages
20
Location
Jefferson Parish, LA
Corvette
stock 98 C5 pewter 145K miles
Thanks for that info . I already have it back together for now . I could jack it up again and pull the tac plugs out and grease the seals which were clean and healthy looking . For now I'm trying to get the horn working . I still have to remove the center of the steering wheel again and I'm not in the mood to work on it . I did grease the seals on both PCM plugs after cleaning them up .
 

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