94 3.0L - Low Power, rough idle

[monsta]

But here's the skinny...

This 94 was given to me. It has been sitting for nearly a year and the guy just wanted it off his property. It's in fine condition except for this low power situation.

You can floor it from a stop and it not accelerate very fast. It does 0-35 in about 25 seconds. It sounds as if it is missing or out of time. It sometimes backfires into the intake under load like when I pull in my inclined driveway

Here's what has been done so far.

NEW - cap, rotor, wires, plugs (Autolite AP104), fuel filter, O2 sensors, air filter, fresh fuel.

CLEANED - MAF, IAC, no vacuum leaks detected, battery was dead has been charged to 13V.

The fuel pump appears new and the screen is not clogged. And I ran fuel pressure test today and it is well within the specs of 30-40psi.

The cat has been gutted (not by me. I just verified it yesterday.) The muffler is not clogged.

I ran all KOEO & KOER tests using the check engine light. 411 & 543 came up.

411 (R) Idle speed system not controlling idle properly (generally idle too high)
Odd because the computer raised the idle. It's fairly low when in gear.

543 (O) Fuel pump monitor circuit shows no power (M) (Service 556 code first if present) Fuel pump relay or battery power feed was open.
I think this is a memory code. Not sure how to clear it.

It starts right up with no issues. And when cold runs and sounds perfect. It's just when it drops out of "warm up mode" that there is what sounds like a miss. Revs drop fairly low when warm and you drop it in gear. Acts like it is missing when you step on the gas.

Questions:

Why would it run/sound fine when in high idle but not when the idle drops to normal?

Could there be an intake leak? Are these 3.0L prone to that?

I keep thinking it's a head gasket but I have no tell-tell signs of a bad head gasket.

 

[Raudi]

I have the same problem. Any advice??

 

[monsta]

I've tested everything 'cept doing a leakdown. I'm pretty sure I have a bad head gasket. I notice that the coolant (water actually) is low and it spits out more than usual when warming up. Since the cat is gutted there really shouldn't be a lot of water coming out since water is a by-product of the catalyst that no longer exists.

There is no coolant in the radiator. Maybe that's what threw me. 50/50 mix really steams up. Plain water can evaporate so fast that it is not as evident.

Since the truck was free I'm just gonna throw some K&W Head gasket stuff in it and see what happens. If it doesn't fix it I'm going to sell it for parts...I'll let you know.

Have you done a leakdown test on your truck?

 

[monsta]

Thanks for the response! However some of your information is not quite accurate.

A leak down test is performed with the heads in place. It is also a better method at determining where any leakage is occurring better than a simple compression test. A compression test will only tell you what compression psi is for each tested cylinder but will not show you why it is low in the event it is low.

A leakdown will actually let you know where any leakage is.

If you hear air escaping from the...

intake = intake valve issue
exhaust pipe = bad exhaust valve
oil fill = rings
radiator bubbling = head gasket
cylinder next to one being tested = head gasket

The K&W stuff will not clog a radiator. But I hear what you're sayin'. Had I bought this truck I probably wouldn't use it. But I got a bit desperate. I do indeed need to do a leakdown first to determine if it is a head gasket. I haven't done anything with the stuff yet because I broke a friggin' bolt off removing the stupid thermostat. Always somethin'...

Thanks for the tip on the ignition module. Anyway to bench test it? I hate to throw expensive parts at it. Money is too damn tight.

 

[monsta]

Weird. Dude deleted his post??

 

[psykostevo]

Ever get it figured out?

 

[pineapplesoymilk]

I gutted the cat on mine and lost ALOT of power soon ill be buying a 2.5 in test pipe and welding a cat onto that

 

[Black2000Ranger]

Did you check your coolant temperature sensor? They control the warm up mode.. If I remember correctly.