1986 d21 2.4, idling way to high, also runs rich and sometimes will not start after driven for a while

[Fargw]

Just bought this truck from a friend and trying to figure out what the problem is. Before I bought it, it was a 2 owner truck, all service records and meticulously maintained. 1 blown head gasket about 10 years ago and about 4 years ago a cracked head which was professionally replaced with a brand new one from a company somewhere in Florida. Just recently he started having this problem with it not starting after it was driven a while. After it sat all night it would start right up. Then this fast idle problem arose. Sometimes it will idle down within a few minutes and sometimes it doesn't. Then there's the issue with what he described as black carbon smoke from the exhaust every now and then. No burning oil, no blow by good compression, no check engine light, normal operating temperature. There is an exhaust leak. Both coils have been replaced, new cap, new wires, new plugs. When the new head was put on, he was told the timing chain and gears were in excellent condition.

I'm suspecting a bad cat due to antifreeze getting in it when the head gasket went and during the cracked head episode. Running rich is most likely adding some raw gas to the cat as well. Also suspect a faulty EGR causing the idle issues and maybe the carbon smoke. Not by any means sure though, I'm a welder by trade, not a mechanic. Especially on anything with a computer. This truck is way too nice to let it waste away, as close to pristine as a 30 year old truck can be. Would appreciate some guidance from someone who knows their way around this year and the z24 engine. Thanks in advance.

[datzenmike]

It's definitely running too rich. There are several causes I can think of.

 

When warmed up the O₂ sensor monitors the oxygen content of the exhaust to keep the mixture at optimum. Several things must be in place for closed loop operation. The ECU needs to know that the engine has warmed up, otherwise it will run in open loop or cold warm up, and provide a richer mixture for smoother running. There is a temperature sensor (not the one for the gauge) that tells the ECU when to switch to closed loop operation using the O₂   feedback. So the temp sensor may not be working or the O₂ sensor is worn out. Two possibilities. I'm not saying to run out and buy these two things just that they should be checked.

 

Take the air filter off and watch the injectors in the throttle body while it's running. Are they dripping fuel? They may just be leaking. The equivalent of a carburetor flooding.

[Fargw]

I appreciate the info, I'll check this and see what I come up with. Any thoughts on the catalytic converter.

[Fargw]

Also, where will I find the temperature sensor you referred to? Thanks.

[datzenmike]

I appreciate the info, I'll check this and see what I come up with. Any thoughts on the catalytic converter.

 

The catalytic converter acts on the exhaust after it's made. It has no input to the EFI or engine running. It's like saying a muffler clamp is causing the engine to run rich.

 

 

 

Forgot to mention the ECU has a self diagnostic program that save faults in the EFI system. The ECU is (I think) under the passenger seat and has a RED and a GREEN LED. RED flashes are 10s and GREEN flashes are ones. A single RED and a double GREEN would be 22 for example. There is also an on/off switch.

 

To check the stored codes warm the engine thoroughly.

 

Turn engine off and check that the switch is in the OFF position.

 

Turn ignition switch to ON (don't start)

 

Both the RED and the GREEN lamps should be ON

 

Turn switch to ON

 

Lamps should display code 23 and 24...... 2 red/3 green and 2 red/ 4 green flashes.

 

Depress gas pedal and release

 

Only a code 24 should display

 

depress clutch and shift lever through neutral into any gear and release the clutch.

 

depress clutch and shift back into neural and release the clutch

 

Code 44 should be displayed

 

If any other codes(s) are displayed, write them down.

 

Turn switch OFF

 

Turn ignition switch off

 

Finished.