88 Suburban Error Code 42???

[dpresto31]

Hello everyone, I have a stumper that has baffled me and even three other mechanics. I have a 88 Chevy Suburban 5.7 350, there has been a problem with the vehicle for about a month now. The burb will start up fine, but after driving for about 10 minutes the "Check engine light" comes on and the vehicle starts running horriable. You can actually feel the thing struggling to fire correctly, there is no power in the pedal and it dies when you slow to come to a stop. Error code 42 continues to show up when I run a diagnostics(Engine spark timing). Now being moderatly familiar with trucks (I attempt to do all of my own repairs, but have never been an employed mechanic)I attempted to fix the problem myself. Here is of list of items I have replaced or fixed.
New distributer
New distributer cap
New rotor
New spark plug wires
New plugs
New coil
New TPS (throttle position sensor)
New fuel filter

I have now exhausted my knowledge on what to do. I carefully read each of the questions and answers in the history on this forum, but I was only able to find one that contained information about error code 42, his solution was to change the coil, I have done so and still have the same problem. My next move will be to disconnect the cat and replace the fuel pump, my question is, would the cat or the fuel pump actually casue an error code of 42? Another clue is that the vehicle engine prior to the "check Engine light" comming on, will idle fine and steady, but touching the pedal so that the vehicle just goes past idle, the engine sputters and wants to die, but if you gas it, it does great. Does any one out there have an idea of what I might do next? I would appreciate any help I could get, thanks in advance.

[Delta Dart]

"would the cat or the fuel pump actually casue an error code of 42?" No. Before you hang any more parts you need to verify that the wires and connections that go from the ignition module to the PCM are undamaged. You could try moving the wires a bit while the symptoms are present to see if anything happens but most likely you will need to look the wires and connectors over with good lighting and if needed ohm out the individual wires to verify continuity.

[dirty dan]

Stop where you are! Code 42 is a EST module or knock sensor error. I would bet that you are almost always accelerating when it codes. The knock sensor and EST module allows the engine to run with the ignition timing as advanced as possible with out damaging anything. It's what allows us to get 15-17 mpg on these burb's. The knock sensor hears the knock and relays the info to the EST Module. The EST module signals the distributor ignition module when to fire.
The ECM self tests the spark advance controls. What it does is when you reach operating temperature, the ECM advances the ignition timing in an attempt to create a knock. If it hears a knock, it retards the timing to make the knock go away and the test is over. If it advances the timing and can not create or "hear" a knock, it thinks it has no control of the ignition timing and lets it go back to the base timing (which should be zero deg).
On some models, if you hold WOT for 5 seconds (engine running), the ECM will pick up the timing again. Don't run WOT with out a load or you'll blow your engine.
Your knock sensor is on the engine block just forward and above your starter motor. It should have 1 wire connected, I can't remember if it's blue or purple. This wire runs to your EST module (square w/4 wire connector) by your Throttle Body.
Check this wire all the way for loose, burned or rubbed through. If you're sure you've got a good connection through the wire. With engine running connect a digital volt meter to the wire by the EST Module. Tap lightly, with a small hammer or wrench, on the exhaust manifold (same side as sensor) and see if your tapping is reflected in your voltage. If not, I would replace the knock sensor. Remember that when you pull the old sensor, antifreeze is going to run out so be prepared and make sure your engine is cool. If you do see a reading change when you tap, recheck your connections from the EST Module to the distributor. If all are good, blown EST Module would be your problem. I think that both of these items will run between $30.00-$50.00 each. Don't buy anything but Delco brand when replacing these parts!!!!!!
Aftermarket sensors from such as AutoZone don't work as well (or at all ) and won't last long. Spend the extra $$ now or you'll be working on it again soon.
If your base timing is set correctly, ( @ 0 deg) you shouldn't be stalling when you idle. While you're working on the truck, to keep it from stalling, you may want to set your base timing to 2 or 4 until you get the problem fixed. Remember that you have to disconnect the black and tan EST wire (by wiper motor on firewall) when you are setting your timing. Be sure that when you get your porblem fixed that you set your base timing back to zero. These old bowties don't have a crank or cam position sensor. If you start with the wrong base your timing curve will be off.
Let us know what you find!

[Delta Dart]

Code 42 does point to the EST module but does it adress the the knock sensor? The knock sensor communicates with the ESC controller.Would Code 43 [ESC retard signal to low] set if a problem exists in the knock sensor circuit?

[dirty dan]

The knock sensor feeds info to the EST Module. The EST Module then feeds info to the ECM. If the ECM thinks it cannot control the ignition timing (a result of no knock created or heard by the self test) it quits trying to control the ignition timing to avoid over advancing the spark and damaging the engine. The old ECM's cannot always pinpoint where the problem is.
I put an oversize cam in an '89 burb and found all this out the hard way. Because of the cam, the ECM could not create a knock. It coded 42 everytime the loop just closed and I applied moderate acceleration. When that happens, it's faster to get out of the truck and push it up to highway speeds!

[Delta Dart]

An 89 light truck 5.0/5.7TBI does not use an electronic spark controller and instead the knock sensor communicates directly to the ECM.

1988 light truck and van use Electronic Spark Control(ESC) . The knock sensor sends the low volt signal to the ESC controller which signals the ECM detonation is occuring.

"The old ECM's cannot always pinpoint where the problem is."
True, but this ECM is sayin code 42. I would troubleshoot it as code 42 for now.

[dirty dan]

"An 89 light truck 5.0/5.7TBI does not use an electronic spark controller and instead the knock sensor communicates directly to the ECM."

Dart,
Yesterday you had (shortly) posted that the '88 5.7 didn't have a knock sensor. I own an '89 Suburban 5.7 TBI and have over 280,000 miles. The knock sensor connects it's one and only wire to the EST Module. Trust me.

[Delta Dart]

Yes I did say that"88 5.7 didn't have a knock sensor" which is of course incorrect and I deleted it to avoid confusion. I misread my equipment chart. Sorry for the confusion.

"The knock sensor connects it's one and only wire to the EST Module"

O.K. but the fact remains. An 89 light truck 5.0/5.7TBI does not use an electronic spark controller and instead the knock sensor communicates directly to the ECM. Not sure of how wires are routed on 88 or 89. Don't own either which is why I cracked a book to get the facts.

Reference material used :Matco Service manual Fundamentals of computerized engine controls and ALLDATA(free at my local library).

dpresto31 please disregard the deleted post and accept my apologies for adding confusion to this problem.

[dirty dan]

http://chevythunder.com/1227747_ecm_198892.htm

Check this link for an ECM accurate wiring diagram. Look for the control module @ C-11. Notice wire labelled "E" in connector. That is the blue wire direct to the knock sensor (called detonation sensor on schematic). This is one of two ECM control systems used on the 5.7 TBI R-1500's. The other is almost identical and can be found at Chevy Thunder.
I have found through the years that the quality of service info from alldata is not much better than the info from Chiltons or Haynes allthough the TSB's are of great help.
I started buying factory service manuals for every vehicle I own. I can usually buy the complete sets on E-Bay for <$100.00. I drive the vehicles until the body starts going away on me.

[Delta Dart]

Dan,
You better start reading your books because your understanding of how the system works or how to troubleshoot is incorrect according to the three books and one data base I have used. I don't own the vehicle in question so all I can provide is an objective opinion based on facts found by doing the research. No wives tales, heresay or antecdotes which often lead to replacing:

New distributer cap
New rotor
New spark plug wires
New plugs
New coil
New TPS (throttle position sensor)
New fuel filter

and the problem is still there.

I dont post very often because I find it very time consuming what with all the reading, but it is worth it because every time I learn a little more about a different system which helps me when I work on my cars.

[california-kiwi]

Hi, If you look down to posting 204 you will see I just went throught the same thing. It about drove me mad. I replaced a lot of parts before getting to the real cause so i hope this helps. I actually had 2 problems at the same time. The same symptoms as yours. Started, ran for 10 mins and then ran roughly, check engine light came on, and finally stalled on the side of the road. The good old and too familiar code 42 came up. I replaced the distributor with one from a good running truck and all was well. Next I replaced the pickup coil in my distributor and put it back in. Boy was I happy, it ran great, no problem. after a week it happened again. code 42. What the real problem was , where the 4 pin connector plugs into the ignition module on the distributor, the white wire, circuit 423 in the manual. The socket inside the connector was open circuiting with just a small tap. This open circuits the EST line and sets the code 42. I cleaned the inside of the sockets with contact cleaner and retensioned them a little bit. I also cleaned the module pins and bent them slightly to increase tension in the connectors. I am happy to report no problems for months now so give that a shot and I reckon you will conquer it. Pete.

[dirty dan]

Kiwi- That's great information, and surely something for dpresto to check assuming he's still having the problem.

Delta- You must not read very well or you would have noticed that I'm not the one who replaced all those parts.
I'm not here to argue with you and I will not respond to any more of your posts.
This forum should be about helping fellow 'burb owners using our knowledge and experience. I own an '89 and a '91 both are R1500's 5.7TBI. Both are high mileage vehicles. For the most part with these old burbs I've "been there, done that". If I haven't, I don't comment. You'll never see me answering questions about your, or any, 1994 Chevrolet Caprice 9C1 LT1 because I've never laid a wrench on one.
If dpresto31 has any more questions, I'll be glad to answer them based on information from the GM Factory Service Manuals and my personal experience.

[Delta Dart]

"That's great information"
I agree . I believe it echos my original advice before you jumped in Dan.

"Delta- You must not read very well or you would have noticed that I'm not the one who replaced all those parts"
I did not say that you did. Just trying to make a point that sloppy troubleshooting leads to wasted time and money.

"For the most part with these old burbs I've "been there, done that"."
Meaningless if you have been doing it wrong all these years.

"GM Factory Service Manuals and my personal experience."
You need to READ the manuals for them to be of any value.

Let me say that with diagnostic t/s an objective mind can be a good thing. Get in ,t/s by the numbers, and get out. Keeping it simple is important as well. Thats what I wanted to do. Say what to check and if they need more info they will ask.

One last thing. I have the FSM books for my Caprice and I don't see any difference between it and alldata pro. Same diagrams and info.

[dpresto31]

I would like to thank everyone for all of the useful information, but unfortunately the problem still exists. I have changed the knock sensor, the EST, checked the wiring harnesses and wires, the problem of error code 42 still reoccurs. It seems that I can temporarily solve the problem by just turning off the vehicle and restarting, the light goes out and the truck runs ok, that is until that old check engine light pops back on. Thanks again for all of the help, does anyone have any other suggestions besides donating the vehicle to charity?

[toivo]

put a vacuum guage on it and see what it reads. if you gun the engine and the guage stays up higher than it should it indicates catalytic plugged.