I drove to the store this morning and everything seemed normal. I went and put in about 4.xx gallons of 87 octane gas at a Mobil station since I was almost on the "E" line. I drove to another store and then drove about 10 miles on the freeway. Drove to the market and when I drove back home, I noticed that the car was idling slighlty under 500 (normally idles at 500 and is stable). This time it seemed to be stumbling as if it were going to turn off but never did. When I got home, I noticed that the catalytic converter was smoking. I turned off the car and when I turned it back on, I noticed that the sound of the engine had changed. It sounds different now. When I was driving back from the market I thought I smelled some type of alcohol smell.

Did I fill up with ethanol or what? That's what I get for filling up with crappy Mobil gas Hopefully I can make it to the nearest shell or chevron gas station to fill up with 91 octane.

UPDATE: I filled up the tank with 91 octane at Chevron and it is still the same. I think maybe the cat is clogged? It sounds like the motor of a boat at low RPMs, like if it were pulling a heavy load. The sound is more like a hum than a distinct V8 sound.

 

Try running a vuccum test. Do one at idle note the reading and how the needles moveing (steady, vibrating quickly, steady rhythmic drops in reading). Then perform the same test but with the car running at 1500 RPMs steady. From this we can figure out alot about how your motors doing overall and detect a clogged cat.

 

I did the vacuum test a few minutes ago. When I first turned on the car, it idled at 350-400RPM and had a vacuum of 10 in.Hg. When it warmed up and went into closed-loop, it idled at around 500RPM and had about 15 in.Hg. of vacuum. When I revved it up to 1500RPM, it went to 20 in.Hg.
The needle seemed pretty steady the whole time. It didn't seem to pulse or anything. It did move back and forth a little bit while I was accelerating, but not while I maintained the RPM. I did notice that the motor sound gets better once I rev past 1000 RPM or so.

 

Well steady is good it will fluctuate a bit when you hit the throttle and being that the vaccum jusmped to 20 hgs at 1500 rpms ide say the cats probably ok too. The problem is the idle vaccum should also be like 20-25 HGs and steady low vacuum is in many cases a symptom of late ignition timeing. So go check out your timing see how she does.

 

I am not saying your cat is bad, however I will advise you to check it anyway.
The only reason for this is because you said it was smoking.
I don't remeber which thread I saw this in, but someone had posted that they were driving their Iroc I believe, and the cat lit of fire. The owner also put up pics, and it was burned bad. Like totaled bad.
Just something to think about.

 

Yea checking it out might be a good idea. Genrally speaking if you have a cat thats plugged to the point that its causeing a problem with the running condition of your car youll see with RPMs engin vacuum tends to decrease. So just because its "ok" dosnt mean its neccessaraly "good". I kinda think the smokeing was result of low vacuum causing the carb to think the cars under heavy load condition which it then enriches the mixture which the motor cant burn effectivly forceing the cat to try and burn it up and doing that causing the cat to overheat and possably start to self destruct inside. Probably not to the point where its noticably "bad" as the vacuume did increase instead of decrease with an increase in RPMs but it may not really be "good" eather.

 

My friend suggested that maybe a cylinder may not be firing because the engine also shakes at the low RPMs. Could that be it? Unfortunately I dont have any tools at the moment.

 

Well unfortunetly not. If it had a miss fire you would see fluctuations on the vacuum reading. I dont really recomend this but if you wanted to test something you could try advancing your timing a bit. If it really is late ignition timing advancing it should clean up a bit. I dont really recomend it though because once you do change the timing, without a timing light, youve got no way to reset the timing.

 

My car did kinda the same thing once... It had no power and idled different. I ended up putting about 5 bottles of dry gas in it which fixed it... after i drove it a while.

I dont have a cat tho, so idk bout that... How long have u ran it since u got that gas? enough to filter it out u think?

 

My money would be on either something in the bottom of the tank may have been stirred up since you were near E or bad gas. Grab some lucas seafoam or other "snake oil" swap out the filter and see what happens over the next day or 2. Seafoam seems to be the best shotgun approach as it's basically a series of petroleum runoff. Should clean and dry the gas for ya. A cat is possible but it would take a total meltdown over a day or two worth of driving and something would really be out of whack with the mixture for that to happen. Low rough idle with steady vacuum the same day as a fill up. Injector or something in the gas.

 

I changed the fuel filter, but it didnt seem to make a difference. I disconnected the 4 wire electronic timing cable from the distributor and the motor sounded better. I checked the timing and the timing mark was somewhat steady on what its supposed to be (I think, since it was really dirty) but I noticed that sometimes the timing mark would appear at the very first \|/ triangle on the right. I also think I hear some noise on the bottom center of the engine. Could it be the timing chain that is going? Or is my ignition module bad?

 

Typically when the control module goes out you won't get a spark. But if you want to double check you can have it tested at just about any autoparts store.

Describe the sound as best ya can or an audio of it would be good. Secondly you can use a stethescope to isolate where the sound is coming from. That will help alot.

Now for the typical round of questions.
What shape are the plugs in? Any that seem abnormal from the rest?
What is the timing at with the 4wire connected off idle 1000, 1500rpm?
If you can't dial in timing with your timing light you can probably skip this step. It should advance out around 30-35 deg.

The timing marks on the stock plate should be something along the lines of this.


Each line is an increment of 2 and each number an increment of 4 starting at 4 ATDC and ending at 12 BTDC.

The vacuum seems a little low at idle. Which could also indicate timing without fluctuations.

But before ya mess with timing check the plugs and what shape they are in. If one fouls out that can throw everything off.

 

I changed the spark plugs and the problem is still there. I unplugged the 4 wire timing cable and the engine sounds better. I checked the timing with the cable connected (8*BTDC) and disconnected (5*BTDC). I remember the timing would be a lot higher than 8*BTDC before when the cable was connected. It used to be off the scale to the left. What could cause it to change?

Also, I swapped the ECM with another one to test it out and got pretty much the same thing so I dont think there is a problem with the ECM, but now I am getting an error code 23. I dont know if this was caused by swapping the ECM or what.

 

Hmm this is startin to get screwy .

What did the old plugs look like?
Is the Emissions label still under the hood?
What's the base timing call for there? Don't change it just curious.
Has the cat given ya anymore trouble since the initial heat spike?
Did ya get a chance to have the ignition module tested?

Code 23
Carbed - Mixture control circuit. <--- suspect

Edit: guess i could have just pulled up the specs sheet for the engine since its in the signature.

 

The old plugs looked wet (as could be expected since i had just started the motor and was in open loop). The center part was still white in parts and brown in others. There was no significant carbon buildup.

The emmisions label calls for 6*BTDC at 700RPM idle. (I've had the car set to 6*BTDC idling smoothly at 500RPM for almost a year now).

Cat hasnt smoked again since the first time and I havent had the ignition module tested.

The car is carbed so the Code 23 relates to the MCS. I dont think this is related to the original problem since the MCS was clicking up until today when I swapped the ECM. It gives the same error code with both ECMs so its not the ECM. Now I dont hear the MCS clicking when I turn on the ignition. I must have screwed up the ECM connector or something. I have the service manual with the troubleshooting steps for the MCS circuit so Im going to troubleshoot it tomorrow morning.

Back to the original problem: Since the problem seems to be alleviated when I unplug the EST connector, this points at the ignition module as being the culprit, doesnt it? The timing mark used to be off the scale to the left (when facing the engine) with the EST connector plugged in. Now it is only 2-3 degrees more BTDC than when the EST connector is unplugged.

 

Could be limp mode too. But the module is definitely a front runner now along with the mixture control. Run the tests and let us know.

Your plugs sound like they are in good shape. And no more trouble from the cat is good news but i would keep an eye on it for a little while once the car is back in working order just to be safe.

 

The mixture control solenoid problem was due to one of the pins on the ECM connector breaking off when I swapped the ECM. I stuck a piece of aluminum foil on what was left of the pin and now the MCS is clicking when the ignition is on.

I took the Ignition control module to get tested at autozone and it failed the Setpoint test. I bought a new one but the problem was not fixed. Any more ideas? Thanks for all your help so far.

I also tested the spark plug wires and they measured between 850 and 1600 ohms (resistance seemed to consistent with wire length).

 

That is some good news. We are getting closer.

What shape was the pick up coil in when you had the dist apart?
Is the timing still riding in the same spots with the new ignition module?
Worn plug wires can slow ya down but shouldn't cause any problems unless they just arent carrying spark. It would be a gradual decline.

Whenever ya get some time and money you might hit up a Delco parts house if one is available and get the broken connector straightened out. Might save some headaches in the long run. But for now it is working so that is a good thing.

Now we get into the ugly part which is perception of the engine...

How is it running at...
cruise
hard acceleration
idle

Any abnormalities...
shaking
sputters
bogging
pinging
backfires
etc...

sorry i know this is elementary stuff and somewhat repetetive but might notice something that wasnt there before.

 

I didnt test the pickup coil when I had the distributor apart. I'll check the resistance of the pickup coil and also recheck the timing ASAP.

With the 4-wire EST connector plugged in:
At idle it shakes and sputters, really low idle under 300RPM, and sometimes it turns off from very low RPM.
As I increase the RPM, the engine sounds bogged down, as if it were pulling a heavy load. Once the RPM increases past 1000-1200 RPM, the sound of the engine becomes more normal and the shaking subsides.
When I drove home the other day (40 miles) on the freeway at 60-80 MPH, I didnt notice anything odd. The sound was quite "normal".

With the EST connector unplugged:
The engine idles a little bit higher (400-500RPM) and sounds better, still shakes a little bit. When I accelerate, it stops shaking and the motor sounds more "normal".

 

Odd that it is only at idle. Kinda smacks of vacuum leak.

But lets carry on with the ignition since it seems to be the primary issue.

If your pick up coil checks out we will be left with one last possibility before ruling out ignition.

You can perform a check from the computer to the distributor with the engine running by grounding the diagnostic terminal AFTER the engine is started. If it throws a code 12 with the engine running it will be a big red flag that the computer isn't recieving a pulse signal from the distributor. According to the books this only works for carb'd models. So your in luck

 

Well just thinking out loud here but it seems to me that for some reason or another your computer seems to want to retard the timing. With the EST connector dissconnected its not a problem because it cant send the commands but with it connected it cuts back on the timing. One thing that i can think of is a bad knock sensor. If the computer detects knocks it will retard the timing to try and stop the knocks. Maby a stretch but worth looking into. Another thing to check is the EGR vavle. Is stuck the can cause low engin vacuum and a rough idle usually associated with a surgeing idle but again worth looking into.

 

I unplugged the knock sensor and it didnt seem to make a difference. I checked the resistance of the knock sensor and it was at about 100K. I also measured the voltage from the knock sensor wire to ground and got 0V. Bad ESC module?

 

Tap the cat, rattle it, shake it, if you hear anything move, that could very well do it.

 

Yea First with the knock sensor they will always put out some very small voltage. From what i understand .08 volts is normal. Now one thing you could try is giving the sensor a sharp tap with some metal tool while the motors running. If the knock sensors working this should retard the timing causeing the RPM to drop a little bit. However because i think the timings already bing forced to max retard this will probably have no effect. However try it because that test will atleast confirm it. Now is it the ESC modual, maby but weve got some trouble shooting to do first. Now the way this whole mess works is theres 4 parts to it 1. the ECM 2. the EST modual in the distributor 3. the ESC modual and 4. The knock sensor. Now normally the ECM controls the advance sending commands to the EST modual that youve already replaced. Now under normal circumstances thats all there is too it. However theres also the knock sensor and the ESC modual that influence the timing when knocking is present. The ECU modual has a single wire (black wire) running to the ECM. When everythings normal the ECU modual sends out a voltage of 8-10v to let the ECM know there is no knocking present. If there should be knocking however the ECU will cut off this voltage telling the ECM to retard the timing. So if you were to have a bad connection or a broken wire and the ECM saw this signal as always 0V it will set the timing to max retard setting. So start by measureing what voltage the ECU modual is putting out on the black wire. Also as mentioned earlier the knock sensor deals with very small voltages (in the milli volt range) so induced noise can have a big effect. The knock sensor may be good but the wire may have induced noise from running too close to the ignition system or charging system that makes the whole system think that the knock sensor is detecting a knock.

 

I measured the voltage at the ECM connector at the wire coming from the ESC and it was about 9V with the ignition on/engine off and also with the engine running.

OldYellr325, I tested the resistance of the pickup coil and it was about 848 ohms. I also tested the resistance between each pickup coil terminal and it was infinite so theres no short to ground there.

I took the car to my neighbor, a mechanic, and he tried adjusting the two mixture screws on the bottom and since the engine didnt seem to respond to changes smoothly, he said that it looks like the carb may have picked up some dirt and got clogged. He said I should try putting some cleaners in the gas tank to see if that clears it up, but if it doesnt, then I should take the car to a carb repair shop. Could this even be the reason for all the problems?

 

Well although i suppose its possable that your carb may have sucked up something that wouldnt account for the low vacuum you described earlier and if the ignition timing isnt right how could the car be expected to respond well to anything? Next thing i would try is dissconnect the ESC modual while the cars running if its working then you should hear the RPMs drop when its dissconnected.

 

I think I unplugged the ESC module and nothing happened, but I will double check. If it turns out to be the ESC module, where would I be able to get a replacement? I checked the Kragen and AutoZone website and did not find it listed.

 

Well if it is the ESC i would say any place should have it but something like that they probably wont have listed on their web site. Give them a call and im sure thell be able to hook you up. Howeve because the ESC modual was putting out 9V I dont think you have to worrie about it. What i suspect is youve got a broken wire between the ESC and the ECM or a bad connection somewhere. This is because by dissconnecting the ECS it should have dropped the 9V signal to the ECM which tells the computer to retard the timing which will cause a drop in RPM. Because it didnt this tells me the comp was already retarding the timing and the only way this could be is if somewhere the signal was getting dropped already. I would start by measureing for the 9V at the ECM harness and if its there checking over the pins for a good connection.

 

http://www.autozone.com/N,16400352/s...eResultSet.htm

After reading more in depth... Im gonna go with no signal to the knock sensor i.e. the 0Vs. According the haynes and chilton it should be around 8-10v for the signal. (Might be wrong though)

The module itself runs about $53 through autozone. And it would have to come from a vendor so probably looking at atleast 3days to get it if they even can.

Call em up and give em ESC105 for the part number and see if they can order it.

Cant always trust their system or site cause the computerized catolog is still somewhat autistic. It doesn't always recognize that its the same part for 20 different cars.

 

Well the knock sensor itself sends a very small voltage to the ESC modual and its very small almost 0V i hear normal is like .08V up to a few milli volts. The 8-10V that there refering to is the voltage the ECS modual sends to the ECM. In this case if the ECM sees 8-10V signal from the ESC it means everythings ok 0V signal means a knock is detected and the ECM will compensate by retarding the timing. Seeing as how he measured the ESC modual to be putting out 9V (meaning no knock is detected no timing adjustments needed) ide say that the knock sensor/ ESC modual is fine or atleast not causing the timing to be retarded. Now again just because the ESC is putting out 9V dosnt mean its actually getting the ECM and i have a strange feeling its not.

 

Good point. Forgive me its late .

Kinda curious as to why the signal would be lost out of the blue on the highway unless a wiring harness grounded. I know on some they run in pretty close proximity to the manifolds.

And as I'm typing this it dawned on me some of them were equiped with an est bypass connector to set base timing... If this was shaken loose unplugged or dirt fouled.... maybe? Were 84's equipped with the bypass?

Mine is 86 and that harness is long gone... If I remember correctly it was a tan wire...

 

As far as I know, the 84s dont have a special wire to bypass the EST. I read somewhere that the way to set the timing was by just unplugging the 4 wire connector coming out of the distributor and that's the way Ive been doing it all along. But if there is a bypass that I never knew about, I would like to know

I'll take my ECM apart and actually measure the voltage coming from the ESC at the trace going to the plug. This way we'll know for sure that the ECM is receiving the voltage. If it doesn't receive it, then it must be a bad ECM connector since I tested the ESC voltage by touching the pin inside the connector with my DMM probe, while it may not actually touch the board of the ECM.

 

Well by dissconnecting the 4 pin EST connector you are putting it into bypass mode. That would take all of the ECMs control out of the picture but thats pretty much whats happening when he dissconnects the EST connector. This is what caught my interest that it ran almost normal in bypass mode. It would seem to me under normal circumstances with no knocks detected that the timing should only be advanced from its base timing. That coupled with the low vacuum reading and the change in sound earlier described which already made me suspect late ignition timing this kinda confirmed it to me. Why all of this happened while he was driving out of the blue who knows i suppose its all gotta break sometime maby when we get to the bottom of it well have a good picture of what really happend to cause all this mess. It always possable that im barking up the wrong tree but at this point it seems likely were on the right track.

 

I'm thinkin we are.

I'll go ahead and quote this verbatum since I don't think it applies to all models.

Locate the VECI (emissions label) under the hood and read through and perform all preliminary instructions concerning ignition timing. NOTE: If instructed by the VECI label, place the Electronic Spark Timing (EST) in bypass mode by disconnecting the single wire connetor. It is a tan wire with a black stripe that comes out of the wiring harness conduit near the rear of the right-hand rocker arm cover. Do NOT disconnect the four-wire connector to the distributor.

Now of all the SBCs I've run across only a couple have this bypass connector. And I have usually done the same as far as disconnecting the 4 wire connector to set base timing with no ill effect. However if his system does have it, it would definitely be a suspect since everything else is "working as intended".

Particularly my camaro and a 90 caddy brougham (olds 307).

Would sure be a kick in the ***** if thats all it is.

LOL but I do like a good puzzle.

It's a single wire connector that looks alot like the harness for the O2, except its topside on the engine.

As far as I can figure with the engine running better with the ECM disconnected, perhaps thats what makes this particular port significant. It tells the ecm to pull out more than disconnecting the 4wire to counteract any centripital advance. A little far fetched but anything is possible at this point. I'm startin to run out of ideas. Would explain why my emmissions label wanted 0* advance when the engine always favored 8* using the 4wire method.

 

My car is one of those CA-spec models with no Baro sensor on the firewall near the AC receiver/drier in case it helps with minor differences between CA-only and Federal.

 

I'm not sure if its particular to emissions standards. Mine was federal but the car rolled out of the san diego plant. Is there a tan and black wire that runs to a connector that seems to lead to nowhere or back into the harness. Better yet does the emissions label say to disconnect the EST bypass connector?

Edit: I know that is probably the worst description I could give. But I remember it well now cause I had no idea what it went to when I first came across it. The wire literally came out of the harness into this one wire pigtail and back into the harness.

 

I'll check for the cable when I get out of work Tuesday evening and take a picture of the emissions label.

 

Well there may be differences on different modles and i think theres more than one way to put the distributor in bypass mode but this is how ive always been instructed. Now i know what your talking about the single tan wire that goes from the EST connector to the ECMs "bypass mode terminal" so dissconnecting that will tell the distributor to ignore all commands from the ECM however in this case dissconnecting the EST connector does the same thing as there isnt even a signal to ignore anymore lol. Now its different from modle to modle so i cant say this is the recomended way of putting all distributor in bypass mode for all f bodies. For example TPI motors its a big no no to dissconnect that connector. Although i dont think its stuck in bypass mode if it was then dissconnecting the EST harness would have no effect because it already was bypass mode.

"To properly set the ignition timing, the EST must be placed in the bypass mode.

1. On the 2.5L engine, refer to the emission control label for the procedure.

If the label is missing or unreadable, contact your Chevrolet dealer for a replacement.

1. On 2.8L and 5.0L carbureted engines, disconnect the 4-wire EST connector at the distributor. (Fault code 42 may be set in ECM memory, and must be cleared once the procedure is completed). Proceed to Step 7.
2. On 2.8L, 5.0L and 5.7L fuel injected engines, with the engine RUNNING and all accessories off, use a jumper wire to connect diagnostic terminal B and ground terminal A of the 12-terminal Assembly Line Diagnostic Link (ALDL) usually located under the left side of the instrument panel. DO NOT disconnect the 4-wire EST connector at the distributor. Aim the timing light at the timing mark; the line on the balancer or pulley will line up with the timing mark. Increase engine speed and check for timing advance. If the timing still advances with engine speed, perform Step 6. If timing does not advance with engine speed, proceed to Step 7. "

 

I'm not sure which engines they are talking about. They don't specify. It is probably related to the smaller engines.

All they say is if instructed disconnect this connector then time it.



If this isn't the issue I'm at a loss as to why the computer would feel the need to pull it back beyond base timing unless the ESC itself is sending bad info.

 

Well that was just a portion of the whole thing specifying how to put it into bypass mode and the #1 instruction under the "If the label is missing or unreadable, contact your Chevrolet dealer for a replacement" states that for 2.8 and 5.0 carbed motors all thats needed to be done to accomplish this is to disconnect the EST connector. Aside for from how to set EST bypass mode though in the EST bypass mode it should revert to its base timing in the low RPMs and this should be as far as it goes. In bypass mode there should be no ECM control and no retard signals so it should never go below base timing. To my knoledge the only means of retarding the timing is on the ESC's command. Now weve measured the output of the ESC modual to be good sending the 9V everythings ok signal however even though the ESC modual is putting out a good signal dosnt mean the ECMs actually recieveing it. So if there were to be a broken wire or something between the ESC and the ECM all the comp would see is a constant 0V signal indicating a knock telling the ECM to retarding the timing constantly. This is what i suspect is happening but we will know shortly.

 

Unfortunately I didnt have time to look at the car today. I'll post up a picture of the emissions label and also look for the bypass wire ASAP.

Thanks for all your help so far.

 

I didnt see any wire similar to the one in the picture OldYellr325 posted, but wouldnt that wire and connector come from the ECM? If thats the case, I can just take a look at the ECM pinout and see if the pin is there or not to double check.

The emissions label says:

"1. Distributor: Disconnect four wire connector. Set ignition timing to specification with engine running at speed indicated. Reconnect four wire connector. Clear ECM trouble code."

 

ok that means there isnt a bypass connector. So that leads us back to why is the ecm being stupid. Thunder is most likely right in that the esc signal isnt reaching the ecm. I was hoping that was due to a bypass. No such luck lol.

 

Well the thin you do have that wire but it goes to the EST connector so by dissconnecting the EST connector you dissconnect it in the process. Not sure why some have that seperate connector just for the EST bypass line but im sure theres some reason.

 

Long time since I originally posted, but the car all of a sudden started working correctly a few days ago. The engine no longer makes the car shake and it has a somewhat normal idle too. Not exactly sure what fixed the problem, but I have been putting premium gas and I also put a whole bottle of Seafoam two tanks ago.

The carb was adjusted to minimize the problem I had before, so now that the problem is no longer there, I need to get the carb tuned correctly. The two screws on the bottom were adjusted so I need to adjust those back.