Rerock
02-18-2008, 12:36 PM
Symptom:
The truck would have normal power up to about ¼ pedal. Between ¼ and ½ pedal the trans would downshift, the engine RPM’s would climb, but there was no power. Anything above ½ pedal and the motor would bog, pop and backfire. Throttle back below ¼ pedal, all was fine. The truck had ran like this for a year. I thought the torque converter and/or trans was on the way out; so I left it. Trans got smoked last summer (July) while towing one really hot day. Threw in a new trans and torque converter. Trans works great, bogging motor issue persisted.
About a month after the new trans (late August), the wife reports something rattling with the exhaust. Test drive shows the catalytic converter. I thought it was simply chunks of cat plugging the outlet, blocking exhaust flow, causing the engine to bog like it had been (since it wasn’t the trans). Also, when the headlight or parking lights were turned on, intermittently the dash lights would go out, and the gauges would stop working. The oil pressure and fuel gauge would max out, and the coolant temp and voltage would drop to 0. At this time the turn signal indicator lights would turn on dim (not flashing), and the high beam indicator light would come on full. As you rotated the dimmer knob down, you would see the “Check Gauges” light start to get brighter from off to very dim. Sometimes “slapping the dash” would get the gauges to snap back, sometimes not. Later, once the weather turned colder, the wife reported that once the cab was warm inside, the dash would glitch, but then after about 20 minutes, would come back on. I tore the dash apart looking for chaffing wires or bad connections (ground issue?), but didn’t see anything out of the ordinary that could cause the issue.
Fast forward to last week, I was driving the truck on a 35mph road. All of a sudden the power went away. It would idle, but ANY amount of throttle and the motor would hiccup and almost die. Let it back to idle and it would revive. I was about a block away, so I limped it home. The hill on the driveway never seemed so big…
Repairs:
I pull the truck in to the shop, and start by cutting out the catalytic converter and muffler. I accidentally neglect to disconnect the battery, and proceed to weld in the new muffler. While welding, my curiosity grows if the truck will run better with the old cat and muffler gone. When I finish with the muffler, I fire up the truck to see if the issue might have been from plugged exhaust. Keep in mind that I had not replaced the cat yet, so the exhaust was essentially open headers at this point. The truck fires up, but is idling a little rough. I rev the motor up to about 2500-3000 and it sounded like a carburetor that needed to be cleared out. I let it idle for a few minutes, then revved it up 5 or 6 more times, at which point it bogged out and died. I had the passenger side of the truck jacked up and knew the gas was low, so I just thought that the pickup tube was dry. I weld in the rest of the exhaust, lower the truck (now level), and fire up the truck. Motor turned over just fine, just didn’t start. Did some poking around, and every part with in sight said “Delco” or “GM” on it. ‘It could stand some new parts’ I thought. I started replacing parts 1-by-1, then tried starting the truck to see if that part got the truck to start. I work at an auto parts store, so I’m not paying retail… Here is what I have replaced so far:
Catalytic Converter (well straight pipe)
Muffler
Oxygen Sensor
Fuel Filter (completely plugged, don’t know how gas got through)
Fuel Pump
Fuel Pressure Regulator
Ignition Coil
Pick Up Coil
Rotor
Cap
Wires
Plugs
Coolant Temp Sensor ($2.49, why not…)
MAP
TPS
IAC
Serpentine belt (Maintenance)
Water Pump ($11.00 why not…)
Replaced broken EGR solenoid outlet vacuum line (going to diaphragm [which tested good by the way])
A OBD1 code reader for GM vehicles (88-95) says all is well with the ECM and no other codes are present. No internal ECM circuitry errors, shorts, etc. ECM is presumably good. Neighbor has a TBI 350 in his garage complete (with ECM) from an identical truck as mine. He said I could try his ECM to test but, haven’t taken him up on it yet.
I Ran 4awg wires from cab-to-frame, block-to-frame, and block-to-cab. No effect on starting.
Fuel injectors are spitting gas like they should, spark (out of cylinder, hooked up touching header) is really strong; and there is no air cleaner, so it should be getting air right?? Pull a plug and it has gas vapors on it, so fuel is making it to the cylinders.
I verified that the timing mark on the Harmonic Balancer was at 0* BTDC, and that the ignition rotor was pointing directly to the #1 cylinder; just to make sure the distributor wasn’t 180* off or something.
I then checked compression on each cylinder. With fuel/air mixed, it showed an avg of 50.125psi; half were at 45psi, couple at 48, 1@55, 1@62. The motor did not smoke, which to me, is a tell-tale sign that the rings are shot.
After all this, the truck is STILL doing the exact same thing after it puttered out after the exhaust test. Nothing has any sort of impact on how the motor starts. Still has good fuel, still has good spark.
Tonight I am going to check the timing chain/gears to see if the chain is stretched and/or the marks on the gears line up properly. Hopefully they don’t and the mechanical timing of the motor is just off; like a sloppy timing chain skipped 2+ teeth while revving the motor up with no backpressure. If they do line up, I will then remove the cam and check for flat spots. Perhaps the cam flattened out causing the valves not to open/close properly. I have a new timing chain and gear set on hand to replace the factory stuff. I will source a cam if needed.
Truck currently has about 160K miles on it. I have a receipt (somewhere) from the previous owner stating that he had a ‘valve job’ done on it; which would be about 10 years or 30,000 miles ago. I could look at the receipt to see exactly what was done; top end work at any rate.
I think that’s about it. If my grandpa hadn’t given me his truck (he handed me his keys and stopped driving), I’d simply scrap it; but that’s not an option.
I’m not opposed to a crate motor, but I want to know for certain what the issue is before buying one. Ponder the Fathoms of suck brought after throwing $5,000 at a new motor to find out it was a stupid fuse or something; I’d record me kicking myself in the nuts and make a looping video of it… Luckily I'm only about $375 in to it so far.
So WTF am I missing?
The truck would have normal power up to about ¼ pedal. Between ¼ and ½ pedal the trans would downshift, the engine RPM’s would climb, but there was no power. Anything above ½ pedal and the motor would bog, pop and backfire. Throttle back below ¼ pedal, all was fine. The truck had ran like this for a year. I thought the torque converter and/or trans was on the way out; so I left it. Trans got smoked last summer (July) while towing one really hot day. Threw in a new trans and torque converter. Trans works great, bogging motor issue persisted.
About a month after the new trans (late August), the wife reports something rattling with the exhaust. Test drive shows the catalytic converter. I thought it was simply chunks of cat plugging the outlet, blocking exhaust flow, causing the engine to bog like it had been (since it wasn’t the trans). Also, when the headlight or parking lights were turned on, intermittently the dash lights would go out, and the gauges would stop working. The oil pressure and fuel gauge would max out, and the coolant temp and voltage would drop to 0. At this time the turn signal indicator lights would turn on dim (not flashing), and the high beam indicator light would come on full. As you rotated the dimmer knob down, you would see the “Check Gauges” light start to get brighter from off to very dim. Sometimes “slapping the dash” would get the gauges to snap back, sometimes not. Later, once the weather turned colder, the wife reported that once the cab was warm inside, the dash would glitch, but then after about 20 minutes, would come back on. I tore the dash apart looking for chaffing wires or bad connections (ground issue?), but didn’t see anything out of the ordinary that could cause the issue.
Fast forward to last week, I was driving the truck on a 35mph road. All of a sudden the power went away. It would idle, but ANY amount of throttle and the motor would hiccup and almost die. Let it back to idle and it would revive. I was about a block away, so I limped it home. The hill on the driveway never seemed so big…
Repairs:
I pull the truck in to the shop, and start by cutting out the catalytic converter and muffler. I accidentally neglect to disconnect the battery, and proceed to weld in the new muffler. While welding, my curiosity grows if the truck will run better with the old cat and muffler gone. When I finish with the muffler, I fire up the truck to see if the issue might have been from plugged exhaust. Keep in mind that I had not replaced the cat yet, so the exhaust was essentially open headers at this point. The truck fires up, but is idling a little rough. I rev the motor up to about 2500-3000 and it sounded like a carburetor that needed to be cleared out. I let it idle for a few minutes, then revved it up 5 or 6 more times, at which point it bogged out and died. I had the passenger side of the truck jacked up and knew the gas was low, so I just thought that the pickup tube was dry. I weld in the rest of the exhaust, lower the truck (now level), and fire up the truck. Motor turned over just fine, just didn’t start. Did some poking around, and every part with in sight said “Delco” or “GM” on it. ‘It could stand some new parts’ I thought. I started replacing parts 1-by-1, then tried starting the truck to see if that part got the truck to start. I work at an auto parts store, so I’m not paying retail… Here is what I have replaced so far:
Catalytic Converter (well straight pipe)
Muffler
Oxygen Sensor
Fuel Filter (completely plugged, don’t know how gas got through)
Fuel Pump
Fuel Pressure Regulator
Ignition Coil
Pick Up Coil
Rotor
Cap
Wires
Plugs
Coolant Temp Sensor ($2.49, why not…)
MAP
TPS
IAC
Serpentine belt (Maintenance)
Water Pump ($11.00 why not…)
Replaced broken EGR solenoid outlet vacuum line (going to diaphragm [which tested good by the way])
A OBD1 code reader for GM vehicles (88-95) says all is well with the ECM and no other codes are present. No internal ECM circuitry errors, shorts, etc. ECM is presumably good. Neighbor has a TBI 350 in his garage complete (with ECM) from an identical truck as mine. He said I could try his ECM to test but, haven’t taken him up on it yet.
I Ran 4awg wires from cab-to-frame, block-to-frame, and block-to-cab. No effect on starting.
Fuel injectors are spitting gas like they should, spark (out of cylinder, hooked up touching header) is really strong; and there is no air cleaner, so it should be getting air right?? Pull a plug and it has gas vapors on it, so fuel is making it to the cylinders.
I verified that the timing mark on the Harmonic Balancer was at 0* BTDC, and that the ignition rotor was pointing directly to the #1 cylinder; just to make sure the distributor wasn’t 180* off or something.
I then checked compression on each cylinder. With fuel/air mixed, it showed an avg of 50.125psi; half were at 45psi, couple at 48, 1@55, 1@62. The motor did not smoke, which to me, is a tell-tale sign that the rings are shot.
After all this, the truck is STILL doing the exact same thing after it puttered out after the exhaust test. Nothing has any sort of impact on how the motor starts. Still has good fuel, still has good spark.
Tonight I am going to check the timing chain/gears to see if the chain is stretched and/or the marks on the gears line up properly. Hopefully they don’t and the mechanical timing of the motor is just off; like a sloppy timing chain skipped 2+ teeth while revving the motor up with no backpressure. If they do line up, I will then remove the cam and check for flat spots. Perhaps the cam flattened out causing the valves not to open/close properly. I have a new timing chain and gear set on hand to replace the factory stuff. I will source a cam if needed.
Truck currently has about 160K miles on it. I have a receipt (somewhere) from the previous owner stating that he had a ‘valve job’ done on it; which would be about 10 years or 30,000 miles ago. I could look at the receipt to see exactly what was done; top end work at any rate.
I think that’s about it. If my grandpa hadn’t given me his truck (he handed me his keys and stopped driving), I’d simply scrap it; but that’s not an option.
I’m not opposed to a crate motor, but I want to know for certain what the issue is before buying one. Ponder the Fathoms of suck brought after throwing $5,000 at a new motor to find out it was a stupid fuse or something; I’d record me kicking myself in the nuts and make a looping video of it… Luckily I'm only about $375 in to it so far.
So WTF am I missing?