Engine light comes on while driving

[rys272]

87 TBI, Finally got all the major stuff fixed runs really good however whenever I drive around town no engine light what so ever, about 10 minutes after I get on a highway going about 100-105 engine light pops right on and doesn’t go off until you shut the truck off or let it cool down for a few minutes so that had me thinking it was something to do with the o2 sensor/manifold temp. Replaced that same thing. EGR is good pretty much all sensors have been replaced except for oil pressure sending unit (have been trying to find one that fits like OEM). have cleaned every ground I can find and searched hard for any ****** wires

Whenever I’m on the highway I don’t find a difference in running rich/lean when it pops on or anything out of the ordinary? Time to buy a obd1 take her on the highway and read it?

 

[Snoots]

Jumper your OBD1 A and B terminals. Without starting the enngine, turn your ignition on.
Your SES light should flash once, then twice. This will repeat 2 more times. Any further flashes will be error codes. You can download the OBD1 info to determine what/where to look for your issue.

Have you replaced any vacuum lines yet?

 

[rys272]

Jumper your OBD1 A and B terminals. Without starting the enngine, turn your ignition on.
Your SES light should flash once, then twice. This will repeat 2 more times. Any further flashes will be error codes. You can download the OBD1 info to determine what/where to look for your issue.

Have you replaced any vacuum lines yet?

Yeah this would work but problem is I’ll need to pull over on the side of the highway and jam a paper clip in there and hope the code doesn’t go away in time so I can read it. Not ideal

 

[fast 99]

Code will be in ECM memory.

 

[gmbellew]

87 TBI, Finally got all the major stuff fixed runs really good however whenever I drive around town no engine light what so ever, about 10 minutes after I get on a highway going about 100-105 engine light pops right on and doesn’t go off until you shut the truck off or let it cool down for a few minutes so that had me thinking it was something to do with the o2 sensor/manifold temp. Replaced that same thing. EGR is good pretty much all sensors have been replaced except for oil pressure sending unit (have been trying to find one that fits like OEM). have cleaned every ground I can find and searched hard for any ****** wires

Whenever I’m on the highway I don’t find a difference in running rich/lean when it pops on or anything out of the ordinary? Time to buy a obd1 take her on the highway and read it?

Like the other post said, the codes are stored for 30 starts or so. You can pull the code now.

there are only a couple of systems that self test that set a light that would go away on the next start. Those are EGR operation and Knock Sensor operation. EGR self tests under steady highway driving. Knock Sensor self tests under light to moderate acceleration.

It is also a potential that the O2 is sensing rich or lean for some reason, but without knowing which one it is difficult to provide better advice.

If it does it consistently every time you get on the highway, I'd highly suspect the EGR system. Could be the valve or the solenoid or a cracked or plugged vacuum tube in that system.

 

[geolee]

I have the exact same problem on my 94 chevy tbi and have tried a couple different egr's and didn't fix it. Last egr I put on was AC DELCO light still comes on the highway. Been driving it like that for years

 

[Sad Sack]

100 - 105 down the highway?? Thats what I call ironing out the kinks! That engine light will seem minor if ya see cherries in your mirror.

 

[legopnuematic]

100 - 105 down the highway?? Thats what I call ironing out the kinks! That engine light will seem minor if ya see cherries in your mirror.

I’m going to take a guess based on OP’s location that’s maple syrup units, 100kph is about 62mph.

Could be wrong though.

 

[Matt69olds]

I’m going to take a guess based on OP’s location that’s maple syrup units, 100kph is about 62mph.

Could be wrong though.

I wondered the same thing!!!

 

[rys272]

I’m going to take a guess based on OP’s location that’s maple syrup units, 100kph is about 62mph.

Could be wrong though.

Yeah Kmph, anyways seems to be code 42 popping up seems like everyone’s got a different answer for this code but most common seems something to do with spark?

 

[gmbellew]

Yeah Kmph, anyways seems to be code 42 popping up seems like everyone’s got a different answer for this code but most common seems something to do with spark?

if you have code 42 randomly popping, I'd be looking hard at the distributor cap and plug wires for signs of carbon tracking indicating spark leaving and zapping the ICM wires. I had a random code 42 for a while until I was going to swap the ignition control module with a spare to see if it was the problem and I saw my 2 month old distributor cap was cracked. I've also had a bad wire from the coil to the cap cause issues.