Ive been doing A LOT of research on CEL codes 42 and 33.

I have been chasing a rough idle and surge/chugging under acceleration. My issue would only occur when at running temperature but now it does it cold or hot.

I disconnected the EGR solenoid/relay/switch and it DID run better(different story different issue;SOLVED) I proceeded to reset all my codes and do another test drive. Code 42 came back 7 seconds after start-up. I drove it around and never saw a code 33. When I didn't see the 33 come back I decided to drive it again, but really rag on it. I drove it like I stole it, literally, burn outs and hard accelerations. I came to a solid stop and started to spin the tires just to show off , as soon as I came to a stop it started running worse but still no 33. To me that could be he bypass module itself or a faulty distributor. It IS the original Dist so I wouldn't be surprised. Once I got on the highway up to about 70 and got it home I rechecked codes and 33 popped up.

I replaced both MAF relays, MAF, and the ignition module/coil. No fix. Tomorrow I will be diagnosing the ECU at my shop. I hear the PROM can come loose over years of abuse.

I'm just wanting some input if anyone else has had this issue. I have a lot of parts standing by to test if I need to; new distributor, MAF swaps, sensors of all sorts. Let's say Christmas came a little early this year and we lost a faithful corvette owner lol.

I believe this to be a sensor or computer issue because it ran flawless two months ago. Vacuum is perfect. Fuel pressure is perfect. Timing is at 6deg. Spark plug and wires are all new and gapped properly. I'm stumped on this one and what makes it worse is I can't communicate with scanners so no live feed. Power directly to the OBD port. Modus scanner and old brick won't communicate though half a year ago I didn't have an issue with it. Not a concern but I know "live feed" will be mentioned to check what grams the MAF is reading at specific RPM.

 

I am sorry that I don't have much to help but i know others will. i am subb'd to follow this through to the solution.

 

What year??? makes a difference in where ECM grounds are located and can go bad....meaning dirty and not making good contact.

I would be looking into WHY you can not communicate withe ECM. Depending on the year...you can pin out the ALDL connector and get the Check Engine Light to flash a code 12....which is why I asked what year it is.

Not knowing if you are going into 'Closed Loop'...I am wondering if your 'burn-off' function is working for your MAF sensor.

The Code 42...I would be looking at the terminal you disconnect to set the timing. And I have had the wore broken in the insulation causing a Code 42.

Communication withe the ECM is PARAMOUNT...and I would get it working then move on from there.

DUB

 

Sorry, I have an 87 automatic. I have been doing the 12 code flash to get these codes. I will diagnose the no communication tomorrow and get back to you.

I popped open the distributor cap, and noticed the ignition module has no plastic shielding on the connectors so the possibility of arcing is high. I heard that this is a common problem. I'll replace the plastic shieldings and go from there.

As for the Burn Off process, the MAF I purchased was from Rich Porter and looks nothing like the original. No more wires. Circuit board with a metal flap that calculates air movement. I can swap with an original MAF to see if it goes away.

 

Try cleaning the throttle body. It's easy to remove and there lots of small passages that can cause rough idle and running if blocked. Use throttle body cleaner.

You might also need to replace the idle air control valve. It screws into the throttle body and is not that expensive. I found mine at Autozone. A new IACV and cleaning the throttle body solved all of my rough idle and surging problems.

 

The throttle body is as clean as a whistle, that's the first thing I did. I made sure the butterfly's were clean as well. And the IAC has been tested and checks out okay. Still, it wouldn't hurt to swap or at least fiddle with it.

I didn't have time to diagnose anything while at work so hopefully tomorrow we won't be so busy. My lead tech recommended we do a fuel injector cleaning with the high intensity cleaner and just flush them out tomorrow. Maybe it'll clean some things up. I will fiddle with the ignition module ASAP. I think that's my issue. Start ups are slow when cold and firing doesn't feel right. Doesn't feel like a steady single cylinder misfire, like every cylinder is slacking.

EDIT: after playing around with the car a bit, revving up and down trying to find a dead spot, I shut the car off and did some research then 10 minutes later came out and the car would start but have worse idle then die on me. I kept trying and trying till I finally decided to hold the key down longer and give it throttle till it finally stayed running. It was rough but once I drove it again the rougher idle went away, back to its normal bad idle if that's makes sense lol. No new codes.

 

I would still try to get communication with a scanner. As you know...it will give you data when running that you really need to know like the INTEGRATOR value, O2 sensor and crosscounts, IAC value...which can tell you if you have a vacuum leak. COOLANT TEMP sensor...which is really important.

If you replaced or plan on replacing the ignition module....I stick with GM myself...but others use other ones...but one thing you want to make sure is that you have the special compound that goes between the ignition module and the distributor base to aid in protecting it from heat.

Hope you get it and can communicate with the ECM.

DUB

 

I understand the importance of communication to the computer. I'll check all the ground straps to the ECU and such. I'll rip the dash apart tomorrow since my LCD display shuts off randomly and a light smack to the surrounding plastic will turn it back on. More diagnostics is needed lol

 

throttle position sensor?

 

New TPS and its adjusted properly. Checked and triple checked with three known working sensors to make sure.

 

Have you tried a different maf ? I put a maf that looked the same as the og but was from a different year it had a different part number think it was from an 85 and mine would would stall out completely upon acceleration. Also check maf for broken or corrosion on maf connectors

 

I have tried three different mass air flow sensors and still no fix. I checked the wires through looms all the way up to the firewall and they checked out okay

 

I believe the '87 has a cold start valve?

 

The MEMCAL has locks on its connector that keep it from coming out. If you have the original EPROM in the MEMCAL then it is soldered in -- can't come loose. Sometimes if aftermarket EPROMs are put in a MEMCAL one or more pins can miss the corresponding socket and get bent (usually under the body of the IC where you can't really see it), like this:



You usually get error code 42 from opening the EST connector to set the timing. It should not show up again after the ECM has been reset.

Error code 33 can be caused by a bad connection between the MAF and the ECM. That could be a corroded pin in a connector or a wire that is broken. The broken wire thing can be very subtle because sometimes the copper wire breaks inside the insulation so it looks OK. If the wire is flexed it will work or not, depending on if the ends of the wires are touching. Running with the MAF disconnected will cause this error.

 

Indeed it DID. It has a block off plate now lol. While I was putting my intake back together I was so frustrated with the tiny little 9th injector line getting in my way I was a little rough and the line leaked like a garden hose upon start up. So instead of attempting to epoxy or purchase a used line I spent 15 dollars on a block off kit. Never had an issue with it. Down here in Florida I don't think a richer fuel mixture will make a huge difference. The coldest it's been this winter was about 34.

And okay, that makes more sense. I'll follow my MAF lines all the way back to the ECU and tug on them while the car is running to see if they'll throw a code. With the computer aware of code 33 does it put the car into a specific closed/open loop system? I read somewhere that it puts it into limp-mode but I'm not sensing a limp-mode at all. Still as peppy as ever, once i'm in second gear and up to speed that is lol.

 

What I have seen is that the engine will die instantly if the MAF is disconnected while the engine is running. You can disconnect it and then start the engine without any problems, though.

It does not put the ECM into limp mode. It is almost impossible to get into limp mode unless the ECM goes into a major failure mode. The ECM can compensate for component failure and just go on working.

 

I replaced my distributor today with a Cardone remanufactured part. I found my culprit, the Tach or signal wire from the ignition module was crushed between the distributor and the intake. Which means the wire was grounding itself at start up and thrown into a specific loop mode.

Car ran flawless just slight hesitation. Shifting was smooth, acceleration no longer surged or hesitated. Timing needs to go up a bit, maybe 8 degrees and it'll be happy. Up until I got home. The check engine light came on and code 33 and 42 came back. Before it would always flash code 42 first, then code 33. Now it's flipped. Code 33 flashed first. I have yet to get communication to the computer. Monday I will have some time to look further into it.

But what I'm thinking is that the MAF is reading too much air flow and the computer naturally throws a code 42 because timing is being retarded by the computer. Am I way off or does that makes any sense?

EDIT: I reflashed and now I have a code 36. MAF burn off/power relay. That's the only relay I have yet to replace. They're cheap so I'll get one at the local parts store.

 

You will get an error code 42 if you open the EST connector to set the timing. 99% of the time that's the reason. You could get the same error if the connector has corroded pins or the wires are broken.

The 4 wire harness coming out of the back of the distributor is also involved in this error, so check that harness and the connector pins.

 

The code 42 did go away once I timed everything and plugged my connector back in. But the code came back after about 20 minutes of highway driving. Code 36, 33, and 42 are present as of 1 hour ago. Today the CEL light has been off but still running terrible. I flashed and the codes are there but not eliminating the CEL.

 

UPDATE: I believe my ignition module connectors to be bad due to having to rig something up because the original connector fell apart in my hand. I have not had time to take everything apart again. Work has been busy.

The codes are still there except no 36 anymore. I think since I have a Rich Porter MAF which doesn't have coding for burn off, it throws a code. But it's not every time. It throws the check engine light randomly now. Always while driving never at idle in park. Could be 15 minutes could be 5. I can feel the car lose power, acceleration lacks, car becomes sluggish and the CEL light comes on. Every time I shut it off it goes away and repeats the cycle. Very confusing.

I found the name of the pigtail I've been trying to hunt down. It's called a Terminal Block. The distributor has two. One with a capacitor and the other comes off of the ignition module, had a ground wire to itself then connects to the wiring harness then straight back to the computer. THIS is the connector that broke on me. I had to rig something together and well it's failing. I can't find the part I need anywhere and the stealership is no help. Junk yard is my only option I was told due to it being a discontinued part.