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Old 04-20-2005, 01:22 AM   #1
Cantesoleares
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Round 3 rough idle, and other stuff too..

89 Chevy Silverado 1500 series 1/2 Ton Truck w/ a 5.7L engine & a 700r4 auto transmission...it is not a 4x4. Recent engine rebuild. (600 miles ago)

ok, when cold the engine idles rough, when warm seems to run fine although the engine temperature runs about 195-210 at hwy speeds. the cooling system is functioning properly....plugs,rotor,cap & wires are all new...as are the air and fuel filter and pcv valve. 02 sensor was also replaced when rebuilt. I recently had trouble with egr system (code 32) was a leaky solenoid and a leaky egr valve....I replaced both. no more code 32's.

no codes are being stored at all. with a chiltons manual and a multimeter I have check the following....TPS, MAP, IAC (cleaned passages and terminals as well),ignition coil...all measurements (I did not deviate from the book) were within specs, I triple checked. Valve Lash is also by the book. I also have checked for vacuum leaks and intake manifold leaks w/ a can of starting fluid, i found nothing. A visual inspection of the fuel injectors while engine running...both injectors seems to be spraying even amounts w/ no erratic streams. I also checked for exhaust leaks, nothing. I pulled the spark plugs....each one of them had light brownish markings on one side. I showed them to a friend and he stated that it appears to be running lean. When I timed it I did so at normal operating temperature in bypass mode @ 4 degrees BTDC (by the chiltons manual).

am I missing something that may cause this condition but does not cause the ECM to store a code? I feel as if I am going
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Old 04-20-2005, 01:58 AM   #2
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Quote:
Originally Posted by Cantesoleares
89 Chevy Silverado 1500 series 1/2 Ton Truck w/ a 5.7L engine & a 700r4 auto transmission...it is not a 4x4. Recent engine rebuild. (600 miles ago)

ok, when cold the engine idles rough, when warm seems to run fine although the engine temperature runs about 195-210 at hwy speeds. the cooling system is functioning properly....plugs,rotor,cap & wires are all new...as are the air and fuel filter and pcv valve. 02 sensor was also replaced when rebuilt. I recently had trouble with egr system (code 32) was a leaky solenoid and a leaky egr valve....I replaced both. no more code 32's.

no codes are being stored at all. with a chiltons manual and a multimeter I have check the following....TPS, MAP, IAC (cleaned passages and terminals as well),ignition coil...all measurements (I did not deviate from the book) were within specs, I triple checked. Valve Lash is also by the book. I also have checked for vacuum leaks and intake manifold leaks w/ a can of starting fluid, i found nothing. A visual inspection of the fuel injectors while engine running...both injectors seems to be spraying even amounts w/ no erratic streams. I also checked for exhaust leaks, nothing. I pulled the spark plugs....each one of them had light brownish markings on one side. I showed them to a friend and he stated that it appears to be running lean. When I timed it I did so at normal operating temperature in bypass mode @ 4 degrees BTDC (by the chiltons manual).

am I missing something that may cause this condition but does not cause the ECM to store a code? I feel as if I am going


during engine rebuild did you replace the camshaft and/or timing gears
also maybe have a ignition system check done for a bad wire or spark plug(high resistance)
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Old 04-20-2005, 03:45 AM   #3
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Quote:
Originally Posted by osborste
during engine rebuild did you replace the camshaft and/or timing gears
also maybe have a ignition system check done for a bad wire or spark plug(high resistance)

Yes, I replaced both.
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Old 04-20-2005, 04:19 AM   #4
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Quote:
Originally Posted by Cantesoleares
Yes, I replaced both.

thats good rules out worn lobes on cam and worn gears/stretched chain

have you done a compression test or have one done
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Old 04-20-2005, 04:30 AM   #5
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reading my manual haynes chev/gmc1988-2000 model the5.0/ 5.7 timing should tdc 0 degrees for 88-95 models the 7.4L is 4 deg btdc not out by much but might make a difference if the emission sticker is still on the rad shoud check it for timing spec
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Old 04-20-2005, 04:42 AM   #6
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Quote:
Originally Posted by osborste
thats good rules out worn lobes on cam and worn gears/stretched chain

have you done a compression test or have one done

No I have not....I will do a compression check in the morning. I was also thinking of testing the fuel pressure from the pump (the pump is over 200k miles old) and also running some fuel into a container to check for water or rust contamination....or would this be looking in the wrong area?

Thanx osborste, my experience w/ mechanics is limited...and mainly textbook. I have tried to repair and rebuild a worn out vehicle before (a ford probe) and failed (parts were too expensive, so there wasnt much room for error on my part, and I made mistakes)...I would like to succeed for a change...this is sort of a personal challenge for me.
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Old 04-20-2005, 09:20 PM   #7
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ok...compression check finished.....I removed each spark-plug one by one. Compression on each cylinder was between 115-120. Is this ok?

Also, my chiltons does say 4 degrees BTDC (I rechecked)

......would the elimination of the IAC, TPS, MAP, vacuum leaks, manifold leaks, exhaust leaks, cylinder compression, valve timing, and air filter constitute moving towards the fuel delivery and ignition sections? I did not have a fuel pressure tester (it was a vacuum tester) so I did not get to test the fuel pump today.
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Old 04-20-2005, 10:05 PM   #8
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Quote:
Originally Posted by Cantesoleares
ok...compression check finished.....I removed each spark-plug one by one. Compression on each cylinder was between 115-120. Is this ok?

Also, my chiltons does say 4 degrees BTDC (I rechecked)

......would the elimination of the IAC, TPS, MAP, vacuum leaks, manifold leaks, exhaust leaks, cylinder compression, valve timing, and air filter constitute moving towards the fuel delivery and ignition sections? I did not have a fuel pressure tester (it was a vacuum tester) so I did not get to test the fuel pump today.

you right i looked up the timing 4 deg btdc my book is wrong
fuel psi 9-13 psi on tbi units is this in your book
i was hoping the compression was going to be higher but at least they are close my book has a spec of 150 psi for compression(was the engine at operating temp when you did your test and did you recheck with a couple of squirts of oil in the cylinder(help for a better seal on piston/rings for checking valve seating/head gasket) as for vacuum i don't have a spec for this just a comparision of gauge readings check your book for vacuum test at the intake manifold
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Old 04-20-2005, 10:32 PM   #9
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Quote:
Originally Posted by osborste
you right i looked up the timing 4 deg btdc my book is wrong
fuel psi 9-13 psi on tbi units is this in your book
i was hoping the compression was going to be higher but at least they are close my book has a spec of 150 psi for compression(was the engine at operating temp when you did your test and did you recheck with a couple of squirts of oil in the cylinder(help for a better seal on piston/rings for checking valve seating/head gasket) as for vacuum i don't have a spec for this just a comparision of gauge readings check your book for vacuum test at the intake manifold
No I did not squirt any oil into the cylinder, the engine was not at operating temp...
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Old 04-21-2005, 11:00 PM   #10
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today, while looking at the engine idle and hoping to have a mental breakthrough, I heard a large hissing sound. At first I thought it was a huge vacuum leak. I then took off the air cleaner to inspect it and the throttle body was opening ALOT. It was sucking in a huge amount of air. The rpm's were not changing though. I turned off the truck....and when I restarted it....it no longer happened
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Old 04-21-2005, 11:32 PM   #11
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Quote:
Originally Posted by Cantesoleares
today, while looking at the engine idle and hoping to have a mental breakthrough, I heard a large hissing sound. At first I thought it was a huge vacuum leak. I then took off the air cleaner to inspect it and the throttle body was opening ALOT. It was sucking in a huge amount of air. The rpm's were not changing though. I turned off the truck....and when I restarted it....it no longer happened

so you still have rough idle?
i'm wondering if the valve adjustment might be a little tight causing the valves not to seat fully giving you the lower compression if you have access to an air compressior(need adapter for spark plug hole or a good blowgun with big rubber tip) try checking the cylinders one at a time with valves closed and piston bottom dead center if the adjustment is to tight holding valves off seat the air will leak out throttle or exhaust or both might find one or two cylinders. maybe check the cylinders you got the lower comprssion first
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Old 04-21-2005, 11:55 PM   #12
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Quote:
Originally Posted by osborste
so you still have rough idle?
i'm wondering if the valve adjustment might be a little tight causing the valves not to seat fully giving you the lower compression if you have access to an air compressior(need adapter for spark plug hole or a good blowgun with big rubber tip) try checking the cylinders one at a time with valves closed and piston bottom dead center if the adjustment is to tight holding valves off seat the air will leak out throttle or exhaust or both might find one or two cylinders. maybe check the cylinders you got the lower comprssion first
I readjusted the valve lash yesterday just to be sure (someone else told me the exact same thing)...heres the thing...it runs excellent when warm....only when its been sitting for over 4 hours does this happen. Idles like crap until the engine warms up then runs great...all except for the warm hwy temps
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Old 04-22-2005, 12:12 AM   #13
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Quote:
Originally Posted by Cantesoleares
I readjusted the valve lash yesterday just to be sure (someone else told me the exact same thing)...heres the thing...it runs excellent when warm....only when its been sitting for over 4 hours does this happen. Idles like crap until the engine warms up then runs great...all except for the warm hwy temps

check the torque on intake retorque the bolts as the engine heats up(expands) it might be sealing a small intake leak
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Old 04-22-2005, 12:35 AM   #14
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Quote:
Originally Posted by osborste
check the torque on intake retorque the bolts as the engine heats up(expands) it might be sealing a small intake leak


read through the posts running hot your plugs light brown (running lean)
need to get fuel psi checked thinking its running lean(runs hotter)not enough fuel delivery(psi regulator or bad injecters or pump ) or vacuum leak(till it warms up)
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Old 04-22-2005, 03:41 AM   #15
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Quote:
Originally Posted by osborste
read through the posts running hot your plugs light brown (running lean)
need to get fuel psi checked thinking its running lean(runs hotter)not enough fuel delivery(psi regulator or bad injecters or pump ) or vacuum leak(till it warms up)
ok...manifold bolts properly torqued, fuel psi is a steady 13.....I do not know how to test the injectors and I cant find the fuel pressure regulator.

When I re-adjusted the valve lash, they were tight (not by much), they did need to be re-adjusted (the lifter raised a small amount when I backed the nut off of it) I had an experienced mechanic watch over me to ensure I was doing it correctly this time....chalk this up to my inexperiece. I will install new spark plugs in the morning and see if it still runs lean.
this did not fix the cold idle problem however. is there another way for me to check for manifold leaks other than the technique I have already used?
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