I can't get a break

348tripower · May 21, 2012, 05:55:30 PM

I have a 93 GMC with a 5.7. Changed the oil yesterday and fuel filter. I knew it had a bit of a rough idle so I cleaned the TBI. Now it really has a rough idle. Plus major spark knock. The distributor was pretty crusty and the cap and rotor. By following Waynes posts I opted to replace them. No change. If I rev this off of 2000 about 2500 it sounds like it is coming apart. Seems to change on how much you tip into the throttle. Really knocks under load. All the plugs were excellent. I pulled nad checked the EGR. Looks good. No problems up till now. I am confused.
Don :cry:

tomslik · May 21, 2012, 07:18:31 PM

sounds like you knocked some carbon loose.
try some top end engine cleaner (if you can find any) and follow directions.....
i wouldn't panic yet

Mac · May 21, 2012, 11:09:07 PM

Quote from: "tomslik"sounds like you knocked some carbon loose.
try some top end engine cleaner (if you can find any) and follow directions.....
i wouldn't panic yet

Tom, I often see the reccomendation to use the product Seafoam sprayed or dribbled into carb or T body while being sure to maintain RPM's. Is this a good top end cleaning technique ?
I can find Seafoam everywhere in my part of the world.

wayne petty · May 22, 2012, 02:24:24 AM

oh!!!...

back to basics... timing... did you disconnect the tan wire where ever its hidden to set the base timing???

you can set the base timing dead stick.. set the harmonic damper marks to your base timing... by bringing the crank around in the normal direction rotation.. stopping without going past the timing mark... then look at the tips of the reluctor and the pick up coil ... are they aligned perfectly???

that is where the ignition base timing needs to be set at..

check it.. once above 400RPM.. the electronic spark control takes over and the timing can be anywhere..

when you replaced the distributer... did you get one with the NEW design reluctor.. or was it a reman OEM style..

below is the OEM distributer..

below is what the replacements should look like... this is a 4.3 V6 version..

do you have the OBD1 scan tool??? can you get me some numbers?

this is TBI scan values.. slightly different than the TPI numbers but very similar...

348tripower · May 22, 2012, 06:25:19 AM

Tom,
I
Sitting here thinking about this this noise may have been happening for a few days. In was pulling a trailer Saturday in stop and go traffic. I thought the SUV next to me had some sort of brake isssue. Each time we took off I heard a strange rattle. I will try some top end cleaner.

Wayne,
I found the tan wire. It is hidden under a cover on the firewall. Has a black stripe in it. I did get the new style distributor. I don,t have an OBD1 scan tool. I did jump the A&B terminals. No codes. I have some Seafoam for cleaning TPI systems. I will read the can today.
Thanks,
Don

Crosley.In.AZ · May 22, 2012, 08:55:06 AM

Years ago, i used to decarbon an engine with water while it ran. Engine at full operating temp, lite dribble of water into the carb as you throttle it up. Black crud would fly out the tail pipe

348tripower · May 22, 2012, 09:41:51 AM

I just finished doing another check. This is running way rich and has very low spark. I was pulling plug wires and got a small poke off of some. I pulled two wires one at a time and put a plug in. The spark is very weak. :?: I did plug in my OTC pathfinder and the lights occilate between rich and lean. Just have to figure out how to set it up for real time.

Mac · May 22, 2012, 10:12:26 AM

Quote from: "Crosley". Black crud would fly out the tail pipe

Probably not great for a catalytic converter.

348tripower · May 22, 2012, 11:36:14 AM

I missed one important part. A week ago the oil pressure gauge was pegged on this. I changed the oil and it went down to normal but the gauge fluctuates. I gotta beleive it turned a rod bearing and the rattle is the piston hitting the head.

Gonna park it for a while. Gotta do something to make money around here. Three jobs waiting. Been spending time on the house too.

Crosley.In.AZ · May 22, 2012, 01:50:39 PM

Quote from: "Mac"
Quote from: "Crosley". Black crud would fly out the tail pipe

Probably not great for a catalytic converter.

when I say "years ago" , it was pre-cat vehicles.

tomslik · May 22, 2012, 06:27:27 PM

Quote from: "Crosley"Years ago, i used to decarbon an engine with water while it ran. Engine at full operating temp, lite dribble of water into the carb as you throttle it up. Black crud would fly out the tail pipe

really cold water works best, thermal shock breaks the carbon up...
i use 44k or GM's stuff, seafoam will work, generally pour 1/2 of it in fairly fast untill it kills the engine , wait 1/2 to1 hr, fire it up and dump the rest of it in at a fast idle and go drive it (it'll * off the people behind you but....

tomslik · May 22, 2012, 06:28:44 PM

Quote from: "Mac"
Quote from: "Crosley". Black crud would fly out the tail pipe

Probably not great for a catalytic converter.

it's prolly dead after 20 years anyway...

wayne petty · May 23, 2012, 01:57:30 AM

were you able to get the former oil filter cut open.

check for broken pleated filter media???

you might want to have somebody cycle the ignition key on and off.. or jump the fuel pump relay contact.. take the fuel pump relay from its outer cover so you can manually pinch it.. then look straight down the throttle bores and see if when there is fuel pressure.. if you have fuel spraying from a blown fuel pressure diaphragm... engine off.. fuel pump running there should NOT be any fuel spraying from the injectors. but there should also NOT be any fuel spraying from the vacuum port in the bottom of the TBI housing..

got a tight fitting deep socket to drop on a breaker bar without much slop.. so you can lay under the engine and rock the crank slightly to listen for loose rods..