So I have made a couple posts on my car that I picked up as a project, I think I have sorted through most of what is there and what the current problems are. I was hoping I could stumble through fixing some of the codes in my first weekend while waiting for the FSM (it is expected Thurs according to UPS) I have come up with a pretty lengthy hitlist to work through starting with the basics and moving up to the electrical issues. I was thinking I would kind of keep a journal to get feedback and maybe help someone else in the process.

First, what I got. It is a 1993 Corvette Coupe with the 6spd manual. It has 95k on it. It is the Dark Green with Tan interior. The body is in great shape, the paint has some blemishes, but it is straight and complete. The interior is a little worn, but nothing terrible with two exceptions. There is a roll cage behind the seats welded in and somebody replaced the nice stock power seats with some red and black Z06 seats. The car fired up great when I was looking at it and I was able to drive it home no problem though I knew it had issues....

At some point, somebody tried to supe it up. There are a lot of under hood mods. The A/C has been mostly deleted, the AIR system has been deleted, the EGR has been mostly deleted, the PCV is just an elbow out of the passenger valve cover plumbed back to the intake, no valve in there (WTF??), the coolant lines to the intake have been deleted, It has some nice long tube headers (not sure on brand) and I was told it has high flow cats (there is a lot of header tape in the area I would expect cats, but I did feel a bit of a bulb under the tape. Are high flow cats significantly smaller than regular stock cats?). There is some kind of after market box under the hood from Aeromotive, probably something to do with the fuel system, but there is no model or P/N so I haven’t figured that out yet. Also, there may be mods to the coolant system as the on dash gauge doesn’t move much above 140, except when I was messing with the car in my drive way and found out the hard way the relays for the fans were busted (yikes!) it got up to just below the redline before I realized what was happening. The car has some oil leaks that I will take care of as I go through it, the pass valve cover is really the only major one. When I got it, it had codes 15, 26, 43, and 66 in the ECM and 74 in the CCM. CCM 74 seems to be intermittent. I clear it, it stays gone for a while, and then comes back. 15 was easy, the coolant sensor was broken. Fixing this really helped the way the car was running as it was definitely rich when I bought it. Still idles high though ~1000-1100. I spent the first weekend cleaning it up and trying to sort out what was wrong and fix the easy stuff. Turns out, not much is going to be really easy, this should be a good learning experience. Car also had a no start (cold temperature before I fixed the ECTS) and cut out on me during a test ride (threw and ASR code and Code 41 for ICM) hopefully this is just a wiring issue, but I don’t know yet. I walked home, got some tools, came back jiggled the ignition/ECM harnesses around and it started right up, I did not think to try starting it right away to see if it was a heat issue, but I drove it home for about 20 mi and this cutout w/in 1 mi of my house......

My goal is to make this into a driver in the most expedient fashion, then add appropriate modifications as budget allows. Here is my hit list:
1. Compression check; did this tonight. I could get at 5 of the 8 cylinders. The front two have header pipes in the way so I can’t get my gauge on and the 2nd on the driver’s side has all kinds of crap in the way. I got 185psi +/-~2-3 on all the cylinders I could get to. Really happy I don’t have to take the motor apart!

2. Check fuel pressure to make sure there are no leaks, haven’t had a real issue, but just want to check it

3. Put a PCV valve back in. Really cheap and should stop oil from getting in the intake, also, hoping it will help with idle and I have no idea why this one be removed and then plumbed back to the intake? I could see maybe a breather.

5. New idler pulley, the current one sounds like crap and this is cheap/easy

6. Coolant system
6a. Check for leaks and fix them
6b. flush coolant system
6c. replace knock sensors. They look like crap and hopefully this takes care of code 43. Even if it isn’t them, with my luck they will go at some point and I will have to drain the coolant again.
6d. Put in 180 thermostat


7. Troubleshoot code 43 if still applicable

8. Troubleshoot code 26

9. Sort out EGR delete, fix associated vacuum leaks

10. Fix A/C delete, fix the code 66, and probably buy the delete pulley/bracket from TPIS. The current delete is crap, they still have the broken compressor in there which has a ton of drag. Unfortunately adding the A/c back in will be way too expensive to tackle right now.

11. Sort out the AIR delete, I think there is drivers side blockage to the exhaust, maybe a cat, could be a mouse nest, don’t know yet.

12. Fix idle if still applicable.

13. Fix oil leaks and change oil

15. Reserved for the other issues I am sure to find

Questions
1. Could code 26 have to do with the AIR delete being done wrong? I don’t yet have the FSM and I get conflicting info for it. Some sites say its EVAPS, Some say Quad driver 1, Haynes Manual (terrible btw, don’t waste your money) says its EVAPS, EGR, and/or AIR relays. Any insight? I threw the $20 EVAPS solenoid at it and the code went out for a bit, but came back; maybe there is an issue further on in the system?

2. What should I do about the EGR? The headers have the ability to have the pipes in, they are currently capped. The exhaust inlet to the intake manifold is capped (may contribute to vacuum leak/high idle) The EGR valve is still there along with the solenoid and the vacuum lines though the line coming from the T to the front of the engine is open, definite vacuum leak. I guess I can either add the system back in or finish off the delete and get the ECM modified to not look for it. Would I then have to add back the AIR system? Don’t think I can afford this right now. Which is the best way to go all things considered?

3. What should I do about the cats? Without the AIR system they wouldn’t last long right? I mean the driver’s side one may already be blocked. How does one find out if there is exhaust blockage and then how do you find out where it is without cutting it all apart? With my hands over both tailpipes, there is noticeably less pressure on the drivers side, but there is still exhaust coming out. I don’t have to pass emissions, if the cat is blocked, does it make sense to just hollow it out or is it worth replacing if I don’t have the AIR. This also assumes the AIR would be a PIA/expensive to add back in, is that true?

4. I want to get a scanner. I have been looking into handhelds as well as the tuner pro software. Question is, what am I better off with? I will have to spend about the same money either way as I don’t have a laptop. Can you reprogram the ECM with a good handheld like the OTC 3499 or is it really only useful for diagnosing a stock car? I like the ability to use it on both OBD1 and OBD 2. Does tuner pro work with OBD 2 or is there another software package? I am looking for the biggest bang for my buck here.

Sorry in advance for any typos, its getting late. Will be glad to clarify anything and I hope this can help other people who might have some of the same issues.

Bill

 

THats the way it came from the factory. Look at the driver side of the intake, see that loop of hose that comes out of the intake and then back in? Thats where the PCV valve is. Strange isn't it?

Both of these are good changes. Yes high flow cats are much smaller than stock cats.

When you replace the idler pulley check the belt as well.
For the remove knock sensors and drain coolant you'll need a big pan to catch the water that comes out of the knock sensors

Not required, the stock one is just fine even if you have your fans set to come on at a lower temp. If you have emissions inspection you need it to get hot. its the way its designed.

That TPIS bracket is very, very nice. I used it when I got rid of the AC on my car.

AIR delete - no cat issue, the cats do not need an AIR feed. Make sure the caps on the exhaust are not leaking and make sure the block off plate on the intake doesn't leak. Make sure the electric fan and associated hardware are gone.
EGR delete - make sure the block off plate does not leak. It will be a few weeks before I can get to my car and see if the relay is still there.

Your cats are fine, some folks wrap them others don't. I will probably be wrapping mine to cut down on the heat.

Scanner - you don't need no stinking scanner.
Maybe datalog software, but you don't need a scanner.
Tunning is accomplished with a new chip in the computer - check the scan and tune section here.
Lots of folks use the Moates stuff.

James

 

Btw...thank goodness for James, 'cause I was gonna ask for the cliff notes

The only thing I'll add is that the stock thermostat is a 180* t-stat. The temp rating is based on when it *begins* to open. On LT1/4 cars, it's fully open between 192*-194*, hence the cruising temp of mid 190s to 200. If you want a cooler cruising temp, you'll need to switch to a 160* t-stat. You'll then typically see cruising temps in the mid 170s to lower 180s depending on cooling system condition, radiator, outside air temp, etc.

Here are what bullet cats look like (attached to the extensions that go from the cats to the resonator under the center of the car):


As you can see, they are quite small.

 

James, found the PCV valve, that is strange. It was there and seemed to be in good working order.

I thought that not having the AIR system will reduce the cat life? The fan and all hardware are gone, even the relay which may be why the ECM is upset. I thought I read elsewhere that all the ECM looks for is the relay?

The exhaust inlet to the intake is blocked. It looks like in order to complete the EGR delete I would just have to make/buy a plate to cover where the valve mounts and then block the little vacuum port on the pass side of the intake. What about the electronics? Should I keep the solenoid in there to keep the ECM happy? Do I have to remove the EGR from the ECM so it doesnt look to it under certain conditions? I thought I read something about that.

96GS#007, I am in New England so I dont really have a reason to go to the 160 t-stat. Sorry for the lengthy post thought it would be better to just make one post instead of a topic for each issue.

so far all the mechanical system checks are coming in pretty good. Starting to look like this will "just" be an electrical cleanup. I am sure I will be back with questions...

 

Got my coolant flush done with new knock sensors and 180 T-stat. Still have code 43 The supplied voltage and the resistance seemed good, maybe there is something wrong at the ECM or PROM? I dont hear a knock and this is just at idle, haven't even driven it.....

I put a vacuum gauge on for the high idle. Anyone know what the vacuum should be? It is idling around 1000 and I had 19-19.5 inHg vacuum (~9.5psi) Is that in spec?

 

Code 43 - did you clear all codes? If so look in the factory service manual for the troubleshooting tree.

I don't have my car near me so I don't know about the egr selenoid - I know its been take out of the tune so its probably gone.

You may want to start looking for a second ECM - they are scarce and expensive used. Finding one would give you options of being able to swap ECM's when the manual says ECM or X. You cannot find them new, they don't exist.

 

Yes, I went to 4.7 on the dash and cleared all the codes. The FSM mentions that an exhaust manifold leak will cause a light knock at hot. I know I have some exhaust leaks, I can see/feel one right over cylinder 3. It also appears to be leaking in front of the drivers side cat. Probably why I dont get as much pressure out of the drivers tail pipe. I will have to quiet things down around the engine to really figure this one out. Maybe I will actually hear a knock when I take care of the exhaust leaks....

I fixed Code 26. They took out the relay when deleting the AIR system. I swapped the relay out of the fan circuit into that one to see if it would work and it took care of the code. Of course then I got a code 28 when it tried to kick the fan on.

I will have to get another relay to check for sure, but I dont think that the computer is putting the SES light on for the code 43. The SES light was out for a while and only came on I imagine when the coolant temp raised enough to put the fan on and the relay wasnt there.

Am I blind or is there nothing in the FSM about high idle troublshooting and what the spec is for vacuum?

 

Oh yea, ECM rebuild is $400 at mamotorworks. That will be a last resort.

 

Do a google or bing search for rebuilders.
I would not use MAM, there are others that folks have had better luck with.

Think about that second ECM idea - its saved me more times than I can count.

 

Looks like it already has a Delphi Remanufactured ECM in it. SVC no.16159278 which I think is correct. Also has a "hypertech power tuning products sticker on it". I will have to open up the PROM cover tomorrow to see what is in it. Sticker says it meets CARB EO Nos D-260-0 thru D-260-9.

Still working on the DTC 43. I went through the DTC chart in the FSM and I feel like it jumps rather quickly to the conclusion that the ECM is bad so I spent the evening testing all the grounds going into the ECM and they all seemed good, the supply is giving it 5V, new sensors, the outside of the sensors is connected to ground, so I think the wiring is OK. Kind of looking like it may be the ECM, but before I do send it away for a month, I am going to get some data logger items and check it out a little bit to see if the circuit is actually reading anything and also see if there are some loose connections that can be fixed. It looks like wherever I go, I will have to send mine in either as a core or to be fixed. I cant find anywhere that I can just go buy a spare Parts kind of seem to be scarce for this car whats up with that?

Another thing I noticed is that the ECM mount bracket is broken, the thing is held in with a tie wrap! It looks like the mounting points on the ECM box are connected to ground, are they supposed to connect to ground when mounted in the appropriate mount? The broken piece coming from the brake booster doesnt seem to be connected to ground. I am hoping that if it is the ECM, some stuff just got knocked a little loose from improper mounting and I can get one of the techs at work to repair some pins or solder joints....