GM TBI on a 1966 283 Engine - Getting a Code 42

[nvestysly]

After introducing myself on the other thread I'm just going to jump in and tell you my GM TBI issue...

I have a 1966 Chevrolet El Camino with a 283 engine, 2bbl, powerglide, A/C and P/S. The vehicle is mostly stock including the engine.

After years of frustration with points & condenser and carburetor issues I thought updating to a 1990's GM TBI was just the ticket. I bought a kit from a company I found via the internet. As you know, there are several kits out there and they all seem very similar to me. The kit I purchased included the wiring, most of the hard parts and some basic instructions and troubleshooting tips. I've spent the better part of 8 weeks trying to get this thing to work. Here are the details:

I was able to install the TBI system in about a week. Ran the return fuel line, changed the fuel sending unit to allow for a return line, installed an external fuel pump (relatively low, near the bottom of the tank), pulled the old distributor, installed the small HEI distributor, attached the TBI adapter plate, TBI, ran the wires.... Presto, the engine started the first time. Wow was I ever happy. The thing ran great and I was giving myself high-five's for doing such a good job. I took the car for a test drive and marveled with the throttle response, etc. Then the check engine light came on - code 42.

Under a variety of conditions I get a code 42 indicating something is askew with the timing/spark. I installed a new ignition module in the distributor today. No change, still get code 42 under a variety of situations - cold engine, hot engine, idling, etc. If there is any consistency to the check engine light turning on I guess I'd say it's during relatively low-speed operation. But I've even had it happen at highway speed.

I don't want to tune and tweak and wring every HP out of the engine like many people on this forum. I just want a vehicle that's reliable enough for my wife to feel comfortable driving it. Unfortunately, that's not the case as this time.

I have a 1320 Electrontics scan tool that allows me to capture data. I can see the point when code 42 is triggered but I have no idea how to diagnose this issue any further.

Any ideas?

[dave w]

Perhaps this link will help? It for a similar TBI system, so the troubleshooting is EXACTLY the same for your TBI system.

http://www.fieros.de/en/v6help/code42.html

dave w

[nvestysly]

Thanks for the reply. I found similar information in the form of a PDF on the gearhead-efi site. I've excerpted the information regarding code 42 and included it below. Most of the troubleshooting tips point toward wiring/connector issues with the odd situation concluding with a faulty ECM.

Guess I'll be getting out the multi-meter and spending some time under the hood and under the dash.

[nvestysly]

An update...

Yesterday when I installed the new ignition module I think I forgot to clear the previous code 42. OOPS!

Regardless of what I did, or did not do, yesterday... I cleared the codes today. I idled the engine for an extended period of time - in total I ran it for probably 40 minutes. What didn't happen? No check engine light today. I may try again tomorrow to see if that trend continues. However, a few odd things happened and they've happened previously so any insight you can provide would be helpful.

1) A few minutes after starting the engine - it was not up to operating temperature of 180 yet - the engine died. No check engine light. I tried to restart and it did not start easily. It turns over fine. Everything seems to work - radio, lights, horn. It catches a time or two but is very difficult to start. I sit there hoping I don't run the battery down. I try starting a few more times and ultimately end up putting the accelerator pedal to floor and hope like he!! it will start. This isn't too bad if it happens in the garage like it did today. But if it happens in traffic it's a BIG problem. This same issue has happened when the engine is cold, when it's hot and everything in between.

2) After 30 minutes of idling the engine the IAC count went way up to around 200 and even higher up to around 250. The TPS was still at approximately 0.50 (after all it's supposed to be idling). But the wacky high IAC count makes the engine rev up to 2000+ RPM. I gently revved the engine even higher and let it come back down but the IAC kept it at 2000+ RPM. I punched the accelerator and quickly released it and it came back down to normal idle with the IAC coming down to less than 20, less than 10 and then settling around 0. What the heck?! This thing has a mind of it's own. More mild versions of this have occurred in the past when I'm driving the vehicle. I hear the hiss/sucking that indicates the IAC is open and the engine doesn't want to slow down. It's usually not an issue but if it clicked up to 200-250 and the took off when I'm idling at a traffic light that would be a BIG problem!

3) One final crazy thing. All the aforementioned stuff had happened and I continued running the engine. Mostly at an idle. Sometimes putting the car in Drive, sometimes running the A/C all in an attempt to see if the check engine light would come on. So now I'm back to idle and the engine just quits - skips a beat and dies. This time it started right back up. As I said, this thing has a mind of it's own.

So the million dollar question is... should I replace the ECM? I can buy another ECM at Summit Racing and put my chips into it. Would this be worth the $75 to see if that's the problem? I simply don't know how to diagnose this TBI system.

[1project2many]

This is some ironic stuff. After spending years fighting points and condenser, you upgrade to a fight with a much more complex system. Usually these swaps do not cause more headaches than they cure.

Could you provide the part number for the ecm? And is it using a stock GM file or one that was modified to match your engine?

Thanks,

[nvestysly]

The ECM is 1227747and was remanufactured although I'm not sure which "brand" it is. The PROM is modified by the guy who sells the kits. I don't know exactly how it's modified (which data) but the seller asked questions about engine size, transmission, A/C, thermostat temp, 2bbl, factory timing spec, idle RPM, etc.

The original chip the seller made for my car was not a good match and I was having additional problems early on. The idle speed was too high in the chip so the computer was trying to compensate for what it thought was low idle. We fixed that with a replacement chip and the car is running much better than it did originally. I didn't put all that into my original post because I didn't want to confuse the issue. However, the check engine light and problems I described in the posts above are persisting.

I looked at Summit Racing for a replacement ECM. They have a 1227747 replacement from Cardone for $74 and a replacement from AC Delco for $107. Both are remanufactured. I'm leaning toward AC Delco although it goes by a newer part number 88999146. I guess the newer number supercedes 1227747.

The seller of the TBI kit is willing for me to return the ECM and he will put it in his truck and run it for several days. That should verify whether the ECM is at fault. While I'm appreciative of the seller's willingness to help that whole process could take as long as two weeks - sending, testing, returning.... On the other hand, I can have a replacement ECM from Summit or any number of other parts dealers today.

A few more details about the system I installed:

- external electric fuel pump is providing 12 psi to the TBI
- MAP sensor
- 180 degree thermostat
- A/C compensation increases RPM in an attempt to overcome the huge load of the A6 compressor
- engine coolant temperature sensor is in the block side of the water (not the radiator side)
- installed new small-cap electronic distributor
- TPS is set to 0.50 volts but sometimes varies a small amount (0,49 - 0.52) after driving the car. It doesn't seem to always return to 0.50
- when the engine is idling normally the IAC is anywhere from 0 to 10, sometimes a bit higher
- the VSS is disabled, as is the knock sensor, any other sensors not mentioned above have been disabled.
- ECM is mounted in the cab, and it has plenty of air around it and is easy to access (it's not way up under the dash)
- the two relays are attached to the bottom of the ECM with adhesive. I did not screw the relay tabs to a piece of metal