Just picked up a 92 TA (305TPI Auto) and it had a code 33, 34, 42 and 44.


Cleared the codes and drove it and they all went away except for the code 42. I thought something was up because it wasn't quite revving liker I thought it should/would. I know the code 42 is EST, so I checked and made sure it was plugged up correctly. It was OK, so I checked the timing. It was at 5-6* and when revved it increased VERY slightly(to 7-8), so it is obviously not advancing. When I found that out I went ahead and replaced the ignition module with another one. It ran the exact same, but I still decided to check the timing. The strange thing is now when I rev it, it DECREASES the timing about as much as it was increasing the timing before, so basically no change. I have no idea what is going on with that and have never seen that before.

Next I replaced the coil with a brand new one and still no changes.

It is weird because the EST seems OK, the coil was replaced, and the ignition module was as well. None of these things netted any changes.

Besides the SES and obviously no timing it runs great. It starts quickly, idles nicely and runs fine. Just low on power, for good reason.

Help me troubleshoot this please

 

Check the knock sensor. If it is plugged in, ohm it. Should be 3500 ohms I believe. You got too many cars man lol.

 

It may be that the ECM is bad. Check the 4-wire connector at the ICM, that one is the interface to the ECM. With a code 42, the items involved are: distributor body grounded to engine block via hold down, ICM, ECM, and the 4 wires between the ICM and ECM.

You already mentioned the EST/BYPASS connector, that too will cause the issue.

With a GM ICM and the EST/BYPASS open, then timing should hold steady until about 1600 RPM. At which time a set amount of timing is added. It varies but usually in the 10 to 12* range.

RBob.

 

Picked up an ECM at the junkyard today. I will check the knock sensor first, then go to the ECm.


Matt, its a 92 black Vert. Got it to cruise around thiss summer1

 

If you get stumped on it hit me up, either here or HPJ and I could look at it for you, plus I'm dying to check out your IROC lol.

 

Nice. I will probably be over there Saturday if you want to come 'help" me out!




Thanks

 

Thanks Rbob,

Replaced the ECM, no change..... The distributor is obviously grounded. Plugging it up to the Snap-on shows the ECM is advancing the timing, but its not showing up with the timing light. Disconnecting the bypass makes no change in the way the timing light sees the timing.


Fuel pressure is good...

The car is weak enough to NOT rev over 4k in nuetral . Cruising around undfer light load is OK, but it doesn't take much throttle at all.

One thing I did notice is that the snap-on shows no knock or knock retard ever. I will look for it next and ohn it out as well.

What do you mean ICM?


Thanks again for yalls help!

 

Any luck? Hit me up, I can ride out there tomorrow and look at it. Does unplugging the est wire have any affect on how it idles?

 

ICM is the ignition control module. Located on the base plate in the distributor. With the EST/BYPASS open is should add advance once the RPM goes over 1600 or so. This is a limp mode feature. Only use a GM ICM.

Don't worry about the knock sensor at this time. If it was open or disconnected it would toss code 43.

RBob.

 

Oh, I know what the ignition control module is, just never shortened it to ICM, thanks. I did replace that with an Advance auto one and the problem stayed the same. Actual, the timing with the stock one showed 5* at idle and 9 over 2500-3000. With the Advance one it was 5* and slightly went DOWN when revved. Wierdest thing I have ever seen.


I did also get a code 44 now for lean exhaust now, the pipe is split after the cat for a 3 ft section, but wouldnt think that would affect it.

Disconnecting the EST makes NO difference in timing on the light, how it runs, or the SES light(obviously)

 

Ignore the lean code for now. The timing is so far retarded that the fuel isn't burning all the way/ burning in the manifolds. I bet the manifolds are a bit warm after just a quick run. I also know for a fact that when you take a knock sensor out of a 98 vortec 350 and install it on a 90, it sets a 42. It also sets a 42 on this same particular car when you wire a potentiometer in place of the knock sensor, set it to 3500 ohms (I'll have to go crawl under my car and double check what the original sensor ohms at) only to have it short out on a header tube after a handful of passes

Edit: looks like the 90 and up 350 cars got the 3900 ohm KS. Still digging to see what the 305's got.

 

This is one reason why I always use GM ICMs, they work the best. With code 42 active the ECM gives up control of the spark timing. Basically, it is the same as when the EST/BYPASS connector is open.

Work on this issue first, as you don't want to drive it that way.

RBob.

 

What am I checking ohms on? The knock sensor pin, to the block or what? I suck at doing that sort of electronics!

Not working on it today, but sometime this week for sure

 

Yes, the pin to block, or pin to body of sensor. Long story short, when I installed my longtubes, they blocked the connector on the knock sensor and I couldn't plug it in or remove it. I had a 98 block in the corner and thought nothing of snatching the sensor out of that and installing it in the drivers side block drain. Apparently, they ohm 100k ohms! I had just installed heads and cam so when it set code 42 I was searching high and low for a problem with the EST, ignition module, etc. Finally when I looked at a complete system diagram I saw the KS is kind of a main component....Problem solved. BTW I'm a driveability tech for a living, work in Raleigh.



I just went out to check the one on my car, but cannot get to the center pin at all due to the header tube.

Another thing to check, check the tan/black est bypass wire from the ignition module to the pcm for either an open condition, or short to ground. The tan/black wire at the pcm is on the larger black connector, its pin 11, but if you read the numbers on the connector tabs, it says pin 7...
Also check your fuses. There is an inline fuse under the hood, should be behind the drivers headlight. See if this diagram works

 

How about setting the timing at *6 advance and changing the fuel filter. Don't forget to plug the EST wire back up after you set the timing with the engine off.

 

The 305 TPI set ups also used a 3.9K ohm (3900 ohm) knock sensor. It goes directly to pin F9 at the ECM, no external filter is used. Connector E/F is the light green one. They have small numbers and letters on them to ID the pin.

Measure from the wire/terminal at F9 to ground (use the ECM case for the ground), it should be about 3.9K ohms if the wire, connector, and sensor are OK.

RBob.

 

Thanks guys. I will check these things the next time I am down there. I appreciate yall coming back to the thread after I check a few things and redirecting my approach.


I will check continuity on the tan wire, look for the fuse and check the knock sensor ohms next.

 

Ok, we got some closure on this one. Started by ohming the knock sensor from the pcm, 4.03k ohms - perfect. Ohmed the tan/black wire from ignition module to pcm, .01 ohms - perfect. Ohmed the white wire from the ignition module to pcm, OPEN! But where??? The wire harness was absolutely perfect under the hood. No loose connections, no errant wires, no chaffed split loom. I figured I would start by checking where the wires passed through the passenger inner fender. Looking through the door gap I could see some chewed up bare wires. Bingo! Pulled the fender liner and found a furry critter had made himself a home and snacked on a few wires. A little solder, heat shrink and electrical tape later, we had a perfectly running car and a working power antenna!









Sorry Chris, I didn't get any pics of the 11's we painted on the road

 

are your fans running all the time too?

 

Rbob showed me the "key on" test. Turn key to on position and watch for the SES light to blink once very quickly and then turn solid. This indicates a good prom chip.

 

Yep, that'll do it! Good catch. Enjoy the car.

 

Looks like someone is praying in the first pic

That mouse did a number on those wires. We had a pet rabbit once that the kids liked to let run loose in the den. Until it chewed on a power cord...

RBob.

 

Thanks again Matt. Teamwork, in between other things I was working on, really helped.


Also, thnks Rbob for the assistance in here....MUCH appreciated.


It runs good now. Well as good as a 305TPI with a 2.73 rear end!

 

glad to hear you got the vert running chris....

 

Curious, in the pics GTA matt posted, if those wires and that connector were to get soaked with water, would it cause and issues?

 

Do you mean the wires we repaired or the existing bulkhead connector? The repaired wires will be fine, the have been soldered and heat shrinked. We added electrical tape just for good measure. The bulkhead connector really isn't a concector, the wires simply pass through it unbroken, and sealer is applied so water cannot get inside the vehicle.

 

You shouldn't be getting too much water in there(with the fender wells in the car), BUT the bulk connecter(like Matt said) is really just a hole that has silicone in it to keep out moisture.


Thanks 88fastgta...Your car is getting ready to look pretty sweet too!

 

Thanks for clearing that up guys! My car was acting up and I noticed those wires were wet so that was my first guess. But it turns out I had to replace my MAF relay as it got wet from all the rain here lately. It's not on it's bracket and was just laying in the corner.