Jaymann27

Info about truck: 1990 4x4 22RE 5 speed 219k miles. Pretty much stock.

So I have been having an issue with my truck for a while. I thought it was misfiring due to an exhaust leak, but after fixing the exhaust leak it is still there. It has actually been getting worse. It seems like a ping/missfire. It happens when it's under load and is more frequent at higher rpms(above 3k). It sounds like someone is rattling a small rock inside a tin can. It also hesitates and loses power when it does it. The tachometer also goes crazy when it does it. Goes up and down when the actual speed of the engine is constant. Cap, rotor and wires, plugs are newish. Timing is correct at 5 degrees BTC.

It has also been getting worse gas mileage than it should and had less power than it should. I know these trucks aren't known for power or mileage, but my 93 was almost the same truck and it had noticeably more power and better mileage.

Also, I was on my way home over the pass one day when my truck started overheating. I checked and the radiator was only half full of coolant. It is not leaking externally that I can see. I filled it up and drove home. I have been checking it frequently and it has been loosing a little. It could just be air bubbles working their way out of the system though. I checked the spark plugs and they do not look fouled.

At first I thought it was head gasket because of the disappearing coolant, but then I did a compression test and got these numbers:
Cylinder #1= 180psi
Cylinder #2= 170psi
Cylinder #3= 170psi
Cylinder #4= 170psi

I am stumped. Has anyone had a similar issue? I have searched the forums and have not found a solution. I have found others with similar issues, but their fixes have not worked for me. Also, to my knowledge the engine has never had any major work on it aside from maintenance.

Jaymann27

Bump.

Jaymann27

Just checked the resistance on both the TPS and AFM and both are in spec. Anyone have any ideas? Bad ECU?

jennygirl

Interesting that the tach goes nuts when it happens- makes me think about ignition related causes since the tach is driven via igniter pulse.

Things you could check to help narrow
• timing
• engine grounds
• condition of rotor & dist cap
• igniter

Perhaps you have a scum inhibited electrical contact somewhere.

If you can rule out electrical stuff, I'd do a valve clearance check and leak down test. If it's actually pre-detonation, that's not good at all. You'd hope that the knock sensor would at least throw you a CEL, but that doesn't always happen.

rworegon

What does the oil look like?

Jaymann27

Thank you for the input. I have checked the timing and made sure it was set at 5 degrees BTDC with the pins jumpered.

I have not checked the engine grounds, but will do so either tonight or tomorrow.

The cap and rotor were replaced about 6 months ago. Unfortunately I no longer have the old ones for testing. They are cheap enough, do you think I should buy a new cap and rotor to test?

I checked the resistance on the ignition coil and it was in spec. I do have another brand new ignition coil that I bought to try and fix an unrelated issue (turned out to be a simple fix, but I have not returned it yet) should I try out the new ignition coil even though my old one tested to be in spec?

Jaymann27

When I check the oil it looks normal on the dipstick. No milky substance or water residue. No milky substance under the oil cap or under the valve cover.

jennygirl

Jaymann- I would only replace the cap n rotor if bad, maybe dirt just got in there

I doubt the coil will be the problem, but might as well check it off. Maybe you'll find some other loose/wrong connection in the process. It's happened to me.

Jaymann27

So I got around to tinkering with it again, and I adjusted the valves. ALL of the exhaust valves were too tight, and 3 of the intake valves were too tight. After this, it drove perfect for about 20 miles. Then, the issue came back again. I checked the valve clearance again and it was still in spec. What are your thoughts? A burnt valve? Something else?

Also, not sure if I mentioned it before, but the disappearing coolant was coming out of the radiator cap. Not sure how I didn't notice that before.

Jaymann27

Bump. Anyone?

Flash319

I would run the truck at night and see if the ignition coil is arcing. They get small cracks and will fail like that. This may cause you tach/missfire. Also a comp test will not always show a bad head gasket. If you are loosing coolent that is prob your problem. Run engine with rad cap off and see if it is bubbling. If it is sucking coolent, even just a little it will cause a lean ping wich will sound like what you describe. Also if you can, pull the spark plags and have a look with a flashligh into the cylinders. If one of the pistons is really clean that may be your leaking cylinder. Steam cleaned piston.

i would put money on headgasket is done.

wallytoo

iTrader: (1)

verify your fuel pressure. lean misfire can emulate those symptoms, except for the coolant loss.