ok here's the deal....

88 chevy astro 4.3 326000 km
FP rock solid @ 12.5 PSI
consistant compression readings between 155 & 170 PSI in all cyl (with or w/out adding oil)
as far as i can tell, no vacuum leaks
exhaust removed between the collector and the cat
ecu throwing codes 33 and sometimes 34 (map and map V low), however voltmeter says voltages are good
heavy carbon deposits on spark plugs
coil resistances check out
pass side manifold bright orange at night after less than a minute under load (driver side maybe, couldn't tell)
idle seems fairly smooth, occasionally backfires through intake
cap, rotor, and wires appear new
will not rev above 1500-1800 rpm (guessing by sound, no tach) in park/neutral
will not accelerate about 5-10 km/h in any gear
coolant temp gauge show normal warm-up/running temp
oil pressure stays in middle of gauge

reason for removing exhaust is it at first seemed like a serious backpressure problem because of the manifold heating up that hot, that quick, however removing the exhaust just made it louder :rolleyes:

my gf was awarded the van in a divorce settlement, so i have no idea of what/how it happened...

any help would be GREATLY appreciated... this beast should blow the doors of my little 4banger mustang :wink:

Astrix

ok here's the deal....

88 chevy astro 4.3 326000 km
FP rock solid @ 12.5 PSI
consistant compression readings between 155 & 170 PSI in all cyl (with or w/out adding oil)
as far as i can tell, no vacuum leaks
exhaust removed between the collector and the cat
ecu throwing codes 33 and sometimes 34 (map and map V low), however voltmeter says voltages are good
heavy carbon deposits on spark plugs
coil resistances check out
pass side manifold bright orange at night after less than a minute under load (driver side maybe, couldn't tell)
idle seems fairly smooth, occasionally backfires through intake
cap, rotor, and wires appear new
will not rev above 1500-1800 rpm (guessing by sound, no tach) in park/neutral
will not accelerate about 5-10 km/h in any gear
coolant temp gauge show normal warm-up/running temp
oil pressure stays in middle of gauge

reason for removing exhaust is it at first seemed like a serious backpressure problem because of the manifold heating up that hot, that quick, however removing the exhaust just made it louder :rolleyes:

my gf was awarded the van in a divorce settlement, so i have no idea of what/how it happened...

any help would be GREATLY appreciated... this beast should blow the doors of my little 4banger mustang :wink:

Astrix

Well my first guess would have been stuck valves, but since you have good compression, I am everything else checks out good, I would say you have either a major restriction between the throttle body and the valves themselves, or a severely Lean running engine.

Check for debris that may be in the throttle body, also check for good movement of the t/b butterfly plates. This is a start, short of pulling the intake, and heads off I don't know what else to tell you. If the plugs have a heavy carbon build up, the intake manifold my be plugged up.

Since you said the exh manifold gets red hot, than that definately has to be a lean running engine.

I just read that you said it occasionally backfires through intake, and that this van is from a divorce settlement. If the ex was pissed and knew anything about cars he could have switch a few of the spark plug wires around. Only switching two would do it. Even one spk plug wire left off or not seated all the way in would do this.

Check the firing order against the spk plug routing and ensure that all are seated in, then bring the engine up to TDC on the compression stroke with 0 degrees showing on the harmonic balancer and pull the dist cap and ensure that it is pointing to #1 spk plug ready to fire.

If your not sure how to do any of the above have a service shop look at it.

Good luck with it.

I just read that you said it occasionally backfires through intake, and that this van is from a divorce settlement. If the ex was pissed and knew anything about cars he could have switch a few of the spark plug wires around. Only switching two would do it. Even one spk plug wire left off or not seated all the way in would do this.

Check the firing order against the spk plug routing and ensure that all are seated in, then bring the engine up to TDC on the compression stroke with 0 degrees showing on the harmonic balancer and pull the dist cap and ensure that it is pointing to #1 spk plug ready to fire.

If your not sure how to do any of the above have a service shop look at it.

Good luck with it.

I knew i would forget to post something i had checked... when we picked it up, there was no serpentine belt... and i'm told he knows little to nothing about cars... I also checked the firing order, and all wires were seated properly... i'll check the throttle body though, i never thought of that.. if the butterfly is stuck, that could cause the ecu to throw a map code since the vac line for the map is after the butterfly, correct?

thanx for the help
Astrix

I knew i would forget to post something i had checked... when we picked it up, there was no serpentine belt... and i'm told he knows little to nothing about cars... I also checked the firing order, and all wires were seated properly... i'll check the throttle body though, i never thought of that.. if the butterfly is stuck, that could cause the ecu to throw a map code since the vac line for the map is after the butterfly, correct?

thanx for the help
Astrix

Yes it looks that way in my illustration.
http://files.automotiveforums.com/uploads/368212map.jpg

Those vehicles are known for the intakes carboning up. You need to run a carbon cleaner thru the pcv line a little at a time. Watch the s--- coming out the tail pipe. Also check the timing and the egr operation. How's the convertor? I hope it is not plugged, causing lack of power.

ok... new info for ya... this problem happened all of a sudden (or so i'm told) he was driving it and all of a sudden it just lost all power and slowed right down.... during the last year or so, it has been driven very little because he doesn't have a license.... i don't know if this helps at all, but i know it makes a slow build up of some sort a lot less likely, since it happened all at once....

thanx for the help
Astrix