I'm stumped, any ideas?

[walleyemaniac]

I've got a '93 Chevy full size pickup with a 350cid. My problem is a rough idle and it seems to cut out once in a while at road speeds, but not real bad at ecelleration. Some times it seems to be running fine and then out of the blue it will start acting up. other times it will do it right off the bat. Right now it won't go away.

This is what has been done so far:

I replaced the distributer cap and rotor, thought it might be cracked, no change.

Took it to the shop he replaced the srark plugs and fuel filter said I was good to go, no change. Have had problems with him before so I take it to another shop. He replaces the coil said it was cracked, on the way home it starts acting up again so I call him to bring it back. He said it had an EGR code the first time but he thought it was the coil so on the second trip he replaces the EGR valve and module.

Ran good for a while (a few days) and started acting up again so I checked for codes and got code 42 Ignition Control Circuit. Manual told me ignition modle or ECM so I repaced the ignition module. Don't want to replace the ECM unless I know for sure. How do I diagnos that?

A couple other concerns are: It smells really gassy the air filter smells of gas really bad and the under side of the air cleaner cover is a little wet not oily more like gas. And my temp gauge moves around a little more then normal. Replaced the thermastat but didn't seem to change anything. It doesn't run hot only about 140 (which kinda concerns me as I put in a 190 thermastat). It doesn't use antifreeze so I'm thinking not a cracked head or head gasket. Haven't had the cooling system pressure checked though so I'm not for sure. It seems like I have good flow from the water pump as well.

Could all of this relate back to an ECM going bad?

I'm starting to think carberation but I don't know anything about those throttle bodies.

Right now it isn't showing any codes just 12 and it's running like [PoorWordUsage].

It's an old truck but it's treated me good till now. I'd like to keep it around for my girls to learn how to drive. It would make a good first vehicle.

Any help would be greatly appreciated I'm starting to pull my hair out and it's getting beyond my knowhow.

Oh ya the first mechanic said he checked the plug wires and they were good thats why they haven't been replaced. They're not to old either.

[Jeremy airjer W]

I'd like to see scan tool data when it acts up. Some things that come to mind would be the coolant temp sensor out of range, an injector going bad, or possibly a bad fuel pressure regulator.

[walleyemaniac]

Is there a way I can check the coolant temp sensor with an ohm meter or something to see if it's bad. I know the temp gauge on the dash is reading lower then what it did. One of the mechanics said something about a temp sensor but I thought he was talking about ambient temp (maybe I missunderstood) not coolant temp. Because of the outside temp the carb would know how rich-lean to mix the fuel. Didn't make sense to me and I couldn't find anything in the book about it.

Any way to check the injectors or the regulator without a fuel pressure gauge? I don't have one but I've read in the manual how to hook one up to check it.

Thanks airjer, gives me some direction to go.

[walleyemaniac]

Another thing I forgot to say when I first posted was that if it is running good in the morning it usually won't act up until the motor comes up to operating temp. It's almost like was on Q some mornings when the problem first started. Thermastat would open up and bam start running rough. Don't know if this will help narrow it down or not, hope so.

[deadeye]

Im thinking o2 sensor or coolant temp sensor, leaning more towards the o2 sensor though.

The o2 sensor isn't accounted for until its heated up so the computer runs on auto-pilot while its cold. For that truck they should be pretty cheap too, obd1 i think is a 1 wire sensor so it should be about 20 bucks.

You can check to coolant temp sensor with a multi meter too (its free to check and free is good ), I would get the book for the specs on it but you should be able to watch the resistance change as you heat it up/cool it down.

Another thing that you could check is if there is any vacuum leaks around the throttle body. Usually its gonna cause a lean situation but you never know.

If it doesn't happen till its warm the injectors are working right. If they were bad it would run poor from the start. Its a sensor issue.

[walleyemaniac]

I checked the coolant temp sensor this morning. Checked the wires from the ECM got 5 volts and thats what the book said, so thats ok. Checked the sensor cold got areading of 4280 ( book says 4450 at 58 degrees) let it warm up it was running about 175 on a thermometer got a reading of 300 (book says 332 at 176 degrees) so I think that checked out. Plugged it back in and the gauge is still only reading 140 inaccurrate gauge I'm guessing. The truck is 17 years old.

Also just checkedoxygen sensor book said I should have a volt reading between .4-.45 with engine not running key on, I had .55. With it running and warmed up it should be moving between .1-.9 volts. which it did jump around, didn't go out of the limits, but it did stay up between .6-.86. Don't know if I should replace or not?

[jeffreyd]

i am guessing leaky spark plug wire. had the same issue on a 350 thing would run like a top then all of a sudden would start missing etc. could not figure it out til one night it starting acting up i opened the hood and saw the spark jump off the engine to the wire. it may not be leaking outward could be a bad wire and just has too much resistance.

[walleyemaniac]

Ya I'm think I'll pull the plug wires after dinner. Only thing I haven't checked myself yet. Just taking that mechanics word for it. Everything else seems to be checking out fine, guess it wouldn't hurt.

[walleyejgr]

pull the vaccum line off the fuel pressure regulator and see if there is fuel present it should be dry another thing to do is start it up and do a power brake load on the engine.apply the brake put it in gear gradually lean into the throttle if it starts to buck on miss then you got a bad plug wire or wires

[1DIRTBALL]

Here's an easy way to check your plug wire's for any spark leak's without going to the trouble of pulling all the wire's. First, wait until it get's good and dark tonight. Then pull your vehicle into your garage. Leave the engine running with the hood up, close the garage door, turn off all the inside light's in your garage. If you have any spark leak's they will certainly show up now! Good luck! 1DIRTBALL

[Jeremy airjer W]

pull the vaccum line off the fuel pressure regulator and see if there is fuel present it should be dry.

this is a throttle body injected setup (TBI). There is no vacuum line to the regulator.

[Jeremy airjer W]

When its running rough unplug the O2 sensor and see if it makes a difference. If it does than the O2 is lazy/stuck rich. If it doesn't than the data you collected is telling you your running rich or your running to lean which can also cause a missfire and high O2 readings.

[walleyemaniac]

Ya, do I feal like an [PoorWordUsage]!! It was plug wires, two of them, one had no spark at all and the other would but not steady. Replaced the whole set (lucky I had a new set stuffed away in the back of the cabinet) runs like a top now. Let my daughter take me out for a drive about 40 miles no problems. Guess I can't take my mechanics word for anything anymore. Probably the last time was the last time anyway, like I mentioned before have had trouble with him in the past.

Thanks again everyone for the help though, I learn alot on here just from reading all the posts. I'll try and return the favor if I can.

[deadeye]

Glad Its fixed. Kind of odd that it would run OK till it was warm but stranger things have happened. Now you got a truck with a bunch of parts that you don't got to worry about.