Service Engine Soon

[RV Guy]

I just cleaned my engine this past weekend on my '86 coupe and tonight was my first time to take it out. In less than a mile on the street the engine stumbled as it was making a shift from second to thrid and the service engine soon light came on. After that the engine seemed to be running fine but the light is still on. I brought it home and shut it off. Now it was a little hard to start but it did start up and idled just fine but the light is still on. I had this same thing happen the last time I cleaned the engine. I took it in and was told that the code indicated something about a sensor. Any ideas before I take in in to the shop this time?
Thanks.

 

[wishuwerehere82]

Could be the Optispark got some water inside it.
You could try drying out with a hair dryer blowing in the vent tube.
The real test would be to read the codes off your OBDII diagnostic port.
Use this guide to read the codes off the dashboard.
http://www.corvettebuyers.com/ecm.html
This way you will know what sensor is causing the problem.

 

[jester]

Could be the Optispark got some water inside it.
You could try drying out with a hair dryer blowing in the vent tube.
The real test would be to read the codes off your OBDII diagnostic port.
Use this guide to read the codes off the dashboard.
http://www.corvettebuyers.com/ecm.html
This way you will know what sensor is causing the problem.

The '86 has the L98 engine = no optispark.
Read the codes and go from there. If it's running OK now, it's probably OK to drive while you're figuring it out.

 

[ZumZum]

How do you clean the engine? Do you use a hose or pressure washer? Chances are (especially with an older C4) you're getting a sensor or relay wet and that causes the stumble until it dries out. Also check your distributor cap and plug wires for any cracks or signs of aging. It's possible that you're getting water into one of those. Again, that might cause a stumble until it dries up.

 

[gmjunkie]

How do you clean the engine? Do you use a hose or pressure washer? Chances are (especially with an older C4) you're getting a sensor or relay wet and that causes the stumble until it dries out. Also check your distributor cap and plug wires for any cracks or signs of aging. It's possible that you're getting water into one of those. Again, that might cause a stumble until it dries up.

Check for moisture droplets in the distributer cap!! It will make them stumble and set the light with usually a O2 Sensor,Pick Up Sensor or Multiple Mis-Fire code,or all!!!

 

[jmccloud]

Misfire after wash

Dry any visible dampness with a rag. Use a hair dryer to get the rest, especially under the dist. cap and ignition wires at the looms. In the dark, lift the hood while the engine is running (not so far that the under-hood lights come on) and look for arcing. If the ignition wires arc and they're dry, get new ones.
It's almost always moisture under the distributor cap. Give the inside a close look for zig-zag 'tracks' that indicate arcing. If you see tracks, get a new cap (not too pricey on an '86).
Check for codes (search above how to do the paper clip - don't spend any money on a code reader!!!!).
In the end, disconnect the ground lead of the battery for a few minutes and it will reset code storage and shut off the service engine light. This will reset your clock and radio stations too, yeckh.
Good luck.
PS Used to do this to the boat after a night rafted up in the fog. Ran lots better.

 

[RV Guy]

Thanks everybody for all of the ideas. Just to let you know I couldn't get it fixed and I took it to my trusted repair shop today. It turns out that the MAS went out. They will get the part in tomorrrow and I get it back then. This turned out to be a rather expensive adventure.

 

[JAKE]

Thanks everybody for all of the ideas. Just to let you know I couldn't get it fixed and I took it to my trusted repair shop today. It turns out that the MAS went out. They will get the part in tomorrrow and I get it back then. This turned out to be a rather expensive adventure.

Are you referring to the MAF - Mass Air Flow Sensor?

If that's the case, and for future information, you can grab one from a similar year wrecked 'F' body or (not as easy to find) Vette for about $50. They're directly interchangable. I even used one off a buddy's 85 Vette and it worked too; that's how I found out my MAF had died.

Just take your bad one with you to match it to the one you find in the yard. Visually check to see if any of the four very thin wires is broken. Most yards will let you install it and fire your engine to see if it works well.

Swapping MAFs is easy to do too. Loosen two clamps and remove one connector, BINGO!

I did it that way many years ago on my 86 and the MAF is still going strong. Same thing with Cruise Control servos.

Jake

 

[RV Guy]

Are you referring to the MAF - Mass Air Flow Sensor?

If that's the case, and for future information, you can grab one from a similar year wrecked 'F' body or (not as easy to find) Vette for about $50. They're directly interchangable. I even used one off a buddy's 85 Vette and it worked too; that's how I found out my MAF had died.

Just take your bad one with you to match it to the one you find in the yard. Visually check to see if any of the four very thin wires is broken. Most yards will let you install it and fire your engine to see if it works well.

Swapping MAFs is easy to do too. Loosen two clamps and remove one connector, BINGO!

I did it that way many years ago on my 86 and the MAF is still going strong. Same thing with Cruise Control servos.

Jake

Thanks Jake, now that I have a rebuilt one hopefully I won't need another for a long long time. Yes it was the MAF.