1990 454 still low power - no codes

[boatwrench]

Thanks for all the help so far. My work schedule on ship keeps me away from working on my Suburban more than I like.

Here's an explanation of what is occuring:
I have been battling a problem with my 1990 2WD 3/4T Suburban, 454cuin (7.4L), THM400 3-spd auto, and 4.10:1 ratio. The odometer is pushing 151K. The majority of this vehicle's mileage is from highway driving. It was used for family vacations across country (2x coast to coast and 4x to midwest IA, MO & MN) from California. 50% of that time towing a 22' 4k lb travel trailer or my Jeep on a trailer at 5K lbs.

In May of 2008 the engine would die, just quit. When it cooled down it would restart and be good for about 100 miles. A dealer in UT replaced the distributor as the bushings were worn and the pick up (?) was cracked. Got me back to California and then made two trips during the summer from San Francisco to LA and back.

On Sep 6, 2008 it ran hot (sans trailer). Checked it out and the Thermostat had stuck closed. I replaced the thermostat and the vehicle continued to run warm. I drove 1K miles round trip to SOCAL later in Sep. and it was warm, but not hot. The fan clutch wasn't working and there was weeping at the w/p. I said heck with it. Recored the radiator, replaced all the hoses, cleaned the fins of the condensor, oil cooler & trans cooler, flushed the heater core. replaced the w/p and fan clutch. Some where along the way the interior lights were left on for several days and the battery was replaced.

Getting ready for my annual Jeep off road trip to Utah it started running like crap. Low power on freeway, sluggish 2-3 shift, the timing was 12* advanced and not settled; swinging from 6-12* BTDC, spec is 4* BTDC, and it threw a code 43 (knock sensor). Here's the link: from this forum

Since then:
Replaced catalytic convertor. (8psi back pressure) 3" exhaust from collector on back. No change
Replaced Vibration dampner (had a squealing belt & harmonic vibration sound at freeway speed also) No change, belt is quiet, vibes less.
Replaced Knock sensor (code 43) Still sluggish, doesn't set codes.

Have now gone back to basics: Mechanical, Fuel, Electrical
Yesterday:
Checked timing measures 4-6* BTDC (spec is 4*)
Manifold vacuum measured with very slight fluctuation (15-17).
Compression test:
1 = 155; 3 = 145; 5 = 155; 7 = 145
2 = 150; 4 = 160; 6 = 150; 8 = 150

Plug condition:
#2 & #8 sparkplug boots were torn.
#7 and #8 sparkplugs were dry fouled (soot or oil) electrodes were black, not the pink carbon color.
The plugs in the vehicle are AC-Delco CR43TS, what the catalouges list as the standard plug.

Air filter element clean. Has 2,500 miles on it.

Fuel:
Have not checked fuel flow or pressure yet. Vehicle has Throttle Body Injection and I can't find a tap to check pressure. In tank pump and sock. Fuel filter has 2,500 miles on it also.

Electrical:
I'll pick up wires tomorrow on the way home from work. The plugs? I can't locate my Mechanics Encylopedia but it had a great explanation of when to change the heat range of the plug. Any suggestions?

The diagnostic check for Code 43 indicates it could also be the ESC module, but with the timing settled down to 4-6*BTDC and no further codes I am leaning away from that.

Thanks in advance,
Tom

[hwyix]

If it runs good at low loads (idle, 10-20 mph, etc..) sounds like a restriction. I would check fuel and exhaust. (filter, pump, disconnect exhaust after header, etc.. yes i know it will be loud. just for quick test should be ok).

[screwballl]

I had a similar problem with my 91 R2500 with 454... in my case after doing some digging, I tried replacing the intank fuel pump, fuel filter, spark plugs and wires, rotor, oil change and checked the injectors which had proper voltage and fuel output.. then someone here (ChevyTech I think it was) mentioned the module.
I replaced the module in the distributor and that took care of it.
The old module would overheat and shut the engine down since the thermal paste was dried up and powdered (I am assuming it was original, but no way to know now since the old one is long gone). Give it a few minutes and it would cool down enough to let me get the 5-10 miles to work. During cooler days/nights (under 70ºF) it would run about twice as long before dying.

I myself did go with the cheaper module, not the ACDelco version but as long as there is enough thermal paste below it, should have no problems.

http://www.partsamerica.com/ProductD...pe=194&PTSet=A

Currently just shy of 164k miles on the ODO (about 15K since replacing it) and no further problems.