ignition problems and code 041

[97vette]

Hello everyone,

I'm hoping that someone on here may be able to help me with this problem, as I'm just about out of options and do not have access to the factory corvette manuals. I have a 1994 lt1 corvette. It has an ignition problem that is driving me off the wall. When the vehicle sits outside for an extended period in the heat (and by hot--I mean 100 degrees heat or thereabout), sometimes (and that's the most frustrating part!) the vehicle power bogs down, especially around 1500-2000 rpms. Additionally, when it is running like this, when you take off quickly from an idle, the car will just barely move forward and then get a big surge of power. Finally, the car gets hot after all these driveability problems start, going north of 240, whereas it normally stays below 210 before it starts running poorly. I've monitored the problem with a scan tool, the computer is retarding the timing around 9% when it starts to bog down, though I have not yet heard any spark knock.

As I mentioned above, this problem only occurs sometimes in the heat. At other times, it runs very well. What most often happens is that I drive it for around 30 miles with no problems at all... the temperature is good (i.e., below 215) and the motor runs wonderfully. However, after I turn the key off and leave the car sitting for a couple minutes, it will run badly (though the idle is still generally ok and higher rpms are ok, a loss of power is evident from 1500 rpms up).

Initially, I suspected a problem with the knock sensor circuit, so I replaced the knock sensors in the block and the knock sensor control module w/ a lt4 ks control module. No luck. The car had had the optispark taken off in the past and replaced with a delteq coil pack ignition system. So, I figured that the delteq setup may be the problem. I replaced that with new plugs, wires, ignition coil, and a new optispark distributor--first a rebuilt unit from a local parts house, then a new ac delco unit from ecklers. The same problem persisted. Next, I figured it had to be a problem with the computer. So, since I could not find a new computer to buy, I sent my computer away to a place that was supposed to rebuild it or junk it if it was beyond saving. They sent the computer back and said it was rebuilt, but, of course, I cannot be absolutely certain what exactly they did to it. I've replaced a number of other things in an attempt to solve this problem (e.g., a throttle position sensor), but to no avail; I've listed the major services performed.

The onboard diagnostics system has not given me much help. At one point, there was a code in the computer for an oxygen sensor. I replaced the sensor and the check engine light went away, but not the driveability problem. Just recently when the car was acting up, I noticed a "sys" light flash on the dash. After doing a little research, I realized that there was a code in the computer for this light, which I could access through "central control" diagnostics on the scan tool. The code was "041". I guess that this may be the best lead that I've got on fixing this problem. Does anyone have a factory service manual with the diagnostics procedure for a code 041? Has anyone else had a similar problem to mine? Help me corvette action center; I'm running out of ideas!

Thanks for reading! Any help is greatly appreciated!

 

[John Robinson]

Couple of thoughts

The ecm receives and evaluates a lot of information from a number of sensors. Some of these sensors only have a single wire which is a ground wire. If you have a bad ground on one of them the ecm starts to adjust how the engine runs. For instance if it loses the ground on the knock sensor it will retard the ignition up to 20 degrees because it thinks it has a knock. The TPS, MAP,Water Temp,EVAP all have grounds that come together in a ground cluster. You need to clean the grounds to the chassis. The one that is probably the most important is the one on the bell housing because it has the ground for the ecm. I had a similiar problem as you discribe in my 93 this year and found the following problems.

1 A broken wire inside the plug to the TPS.

2 The wire to the knock sensor was bare. It also was thouching a plug wire and that was sending a knock condition to the ecm.

3 The ground cluster was corroded and needed to be redone.

4 The MAP was bad.

You did not say but I bet your fuel milage has dropped off drastically.

We tend to think that the sensors have gone bad and replace them and forget that the wireing is also old and brittle and subject to breaking .

Next time it starts to do this stop and with the engine running shake the wireing harness and wires that go to the TPS, MAP etc. and then get back in car and drive it. If it runs better you probable have a broken wire somewere.

Well that is my 2 cents worth good luck

 

[toptechx6]

Assuming your 94 is the same as a 93 (never a good thing) CCM code 41 is for ECM Serial Data Circuit ( loss of communication) This is the communication circuit between modules such as CCM, PCM, and EBTCM.

As John Robinson pointed out wiring could very well be root cause of the problem. Since it only occurs when it is hot, one other suggestion I have would be to try lowering the temp of the PCM when it occurs to see if it returns to normal. I had a similar problem on my Ram pickup, directing a high speed fan at the PCM cooled it enough to verify that it was caused by an internal issue, replacement of the PCM fixed the problem.

Replacement PCM's are available from many sources including this one
http://tinyurl.com/2weql6d

I find it incredible that you have spent so much money throwing parts at the problem and have yet to purchase the correct FSM to do the troubleshooting.:eyerole