1987 r20 check engine light

[jeffinmalvern]

Hi, new member here. I've been a lurker, but this is my first post. The truck below is my daily driver, so I'm not looking to do any radical mods or anything (it's an ugly work truck, but I use it for everything) but I have a few questions....

I have a 1987 r20 with a 350 tbi. The truck runs great, drives great, shifts great (auto trans). It's 2wd. It's ugly. Lately, the check engine light has been coming on after about 5 mins driving, and stays on until I shut the truck off. Then it goes out. There is no change in how the truck runs or drives, but the light is on. Any thoughts on what might be the problem?

What simple things could I do to the 350 to make sure I am getting the best mileage possible, and keeping the engine well maintained? WHen I bought the truck I changed the oil and filter, and spark plugs, wires, cap, and rotor. I also put some seafoam through the gas tank and sprayed the throttle body with  cleaner. I greased the truck completely. Should I put a better air filter on, or anything else? I know the mileage will never be good, and that's not an issue. I just want to make sure that my engine is in the best shape it can be.

Also, how do I tell which auto trans I have?

Thanks in advance,
Jeff

[Captkaos]

Welcome Jeff.  You can pull the codes out of the ECM with a jim clip jumpered to the to right 2 pin slots of the ALDL connector right above your left leg under the dash.  Bend the jim clip, push it in and switch the power on the ingnition (don't crank it).  Then count the number of flashes, the first 3 will be twelve signified by flash, pause, flash, flash.  If there are multiple codes it will flash more than on sequence, count them out and tell us what they are.

As far a mileage goes, keeping it up is the best thing, just make sure the air cleaner isn't clogged, should be fine.  Change the oil ever 3000 etc.

For the transmission, look at the pan and reference it to this picture it will tell you what kind it is.

[jeffinmalvern]

Okay, got the trans figured out- it's a thm400.
when you say a jim clip, what do you mean? is that a special tool, or just like a jumper wire. Sorry for the newb questions, but I've not really worked on my own truck much before.
Thaanks again for all the help.
Jeff

[Captkaos]

When I say Jim clip I mean a metal paper clip.  Anything that you can get in there will work.

[VileZambonie]

LOL, I've never heard of a jim clip either. Must be an Alabama thing

[jeffinmalvern]

Okay, I think i've got the codes.... hopefully I did this correctly

12, 13, 42, 43, 44

does that make any sense?
jeff

[VileZambonie]

12 just basically means there's communication

13= O2 sensor circuit open

42= EST circuit malfunction

43= ESC circuit malfunction

44= Lean condition detected

Has anyone been screwing around under the hood? Unplugging things and such?

#1 make sure the O2 sensor is connected

#2 make sure the ESC module is plugged in and the knock sensor is plugged in.

#3 make sure you have no vacuum leaks.

Now clear the DTC's by disconnecting the negative battery cable for 30 seconds. Reconnect it and road test it. See what comes back

[jeffinmalvern]

great, thanks for all the help.
couple more questions- where does the 02 sensor plug in?
what are esc and est, and where do i find them?
what would cause a lean condition, and how do I correct it?

Sorry if these are stupid questions, I'm very new at working on my own trucks......
jeff

[VileZambonie]

The oxygen sensor is screwed into the exhaust manifold. On your truck it has a single wire pigtail.

ESC is electronic spark control and EST is electronic spark timing.

The esc module is either on a bracket on your intake or bolted to the firewall. The est module is in the distributor.

A lean condition is most often caused by vacuum leaks or low fuel pressure