1990 C1500 rough idle/miss

1990 C1500 rough idle/miss Group: alt.autos.4x4.chevy-trucks Date: Sun, Nov 2, 2003, 1:08am (CST+6) From: snipped-for-privacy@no.com (Tiffany/Steve) Hi folks. I've got a 1990 C1500 with a Goodwrench crate motor (1,500 miles) and a Bowtie Overdrives "Stage 2" 700R4 (450 miles). Shortly after the transmission install, I noticed a very rough idle and distinct miss during idle. At speed, especially WOT, a vibration could be felt. I was initially concerned the vibration was from the transmission, but I am now able to re-create it in neutral/park. I'm aware the torque converter(new) could also cause the vibration, but strongly suspect the engine. I replaced the cap/rotor/wires/plugs last weekend. The wires were recycled from the old motor and highly suspect. The plugs were all carboned (note 1,500 miles on factory motor and new plugs). This really seemed to help everything. A few days later, the truck started stalling - especially after being held at throttle and then let off (ie, approaching a traffic light). I removed the air cleaner assembly and noticed the fuel injectors were practically dripping fuel. Later in the day, the truck flat-out refused to idle. 1,500 RPM without load was OK, but it would immediately die below that. I suspect the engine was drowning in fuel. I replaced the injectors and rebuilt the fuel pressure regulator. I removed the TBI, then inspected and cleaned all passages. Everything went together and the truck was almost "like new" for a day. I still had an intermittent "stumble" at idle, but it was remarkably better. Since then, I've had a couple of trouble codes - sometimes 33, sometimes 34and sometimes both. I spent the entire morning attempting to re-create these codes and checked every component of the emissions system per the instructions in my Haynes book. All input voltages to the sensors from the ECM were within specification, as well as output. Specifically: TPS - 5.010 v input. .06020v throttle closed, 4.3v WOT (smooth direct relationship between throttle position and voltage). Coolant temperatore (ECT) - 5.010v at sensor. 550 ohms resistance with the engine in the 130 degree neighborhood (had been sitting for a while after running). Oxygen sensor - .397v. MAP sensor - power from ECM: 5.010v. 1.1v-1.2v engine running. TPS sensor was inspected earlier in the week, appears to function properly (idle becomes high when disconnected) and had proper resistance per "the book". EGR valve: Confirmed proper operation with a vacuum pump - I noticed an even more horrid idle with vacuum on the EGR. Releasing vacuum caused the "normal" idle to return. ESC: Doesn't affect engine idle (removed harness). Sets 43 (spark control/knock sensor) if I rev the engine outside of fast idle. A gauge connected to the EGR solenoid indicated 18-20 inches of mercury fora split second when the throttle was opened. I know the EGR should open at highway speeds, but is it supposed to open momentarily when the throttle is snapped (ie idle to 1500 RPM)? This morning I noticed the injectors aren't spraying right. I have streams of fuel again and an occasional "drip". Fuel is puddling up and some of the spray is actually landing on the TBI itself. At this point, I think most of my issues are TBI related and not ignition. I can't believe these injectors are bad, but they sure look like it. Unless there's something sensor-related that's causing the ECM to want to run amazingly rich? I'm running out of options here.. does anyone have any ideas?

-Steve

Whats your timing set at? Steve C

1990 C1500 rough idle/miss Group: alt.autos.4x4.chevy-trucks Date: Sun, Nov 2, 2003, 1:08am (CST+6) From: snipped-for-privacy@no.com (Tiffany/Steve) Hi folks. I've got a 1990 C1500 with a Goodwrench crate motor (1,500 miles) and a Bowtie Overdrives "Stage 2" 700R4 (450 miles). Shortly after the transmission install, I noticed a very rough idle and distinct miss during idle. At speed, especially WOT, a vibration could be felt. I was initially concerned the vibration was from the transmission, but I am now able to re-create it in neutral/park. I'm aware the torque converter(new) could also cause the vibration, but strongly suspect the engine. I replaced the cap/rotor/wires/plugs last weekend. The wires were recycled from the old motor and highly suspect. The plugs were all carboned (note 1,500 miles on factory motor and new plugs). This really seemed to help everything. A few days later, the truck started stalling - especially after being held at throttle and then let off (ie, approaching a traffic light). I removed the air cleaner assembly and noticed the fuel injectors were practically dripping fuel. Later in the day, the truck flat-out refused to idle. 1,500 RPM without load was OK, but it would immediately die below that. I suspect the engine was drowning in fuel. I replaced the injectors and rebuilt the fuel pressure regulator. I removed the TBI, then inspected and cleaned all passages. Everything went together and the truck was almost "like new" for a day. I still had an intermittent "stumble" at idle, but it was remarkably better. Since then, I've had a couple of trouble codes - sometimes 33, sometimes 34and sometimes both. I spent the entire morning attempting to re-create these codes and checked every component of the emissions system per the instructions in my Haynes book. All input voltages to the sensors from the ECM were within specification, as well as output. Specifically: TPS - 5.010 v input. .06020v throttle closed, 4.3v WOT (smooth direct relationship between throttle position and voltage). Coolant temperatore (ECT) - 5.010v at sensor. 550 ohms resistance with the engine in the 130 degree neighborhood (had been sitting for a while after running). Oxygen sensor - .397v. MAP sensor - power from ECM: 5.010v. 1.1v-1.2v engine running. TPS sensor was inspected earlier in the week, appears to function properly (idle becomes high when disconnected) and had proper resistance per "the book". EGR valve: Confirmed proper operation with a vacuum pump - I noticed an even more horrid idle with vacuum on the EGR. Releasing vacuum caused the "normal" idle to return. ESC: Doesn't affect engine idle (removed harness). Sets 43 (spark control/knock sensor) if I rev the engine outside of fast idle. A gauge connected to the EGR solenoid indicated 18-20 inches of mercury fora split second when the throttle was opened. I know the EGR should open at highway speeds, but is it supposed to open momentarily when the throttle is snapped (ie idle to 1500 RPM)? This morning I noticed the injectors aren't spraying right. I have streams of fuel again and an occasional "drip". Fuel is puddling up and some of the spray is actually landing on the TBI itself. At this point, I think most of my issues are TBI related and not ignition. I can't believe these injectors are bad, but they sure look like it. Unless there's something sensor-related that's causing the ECM to want to run amazingly rich? I'm running out of options here.. does anyone have any ideas?

-Steve

Also when you changed your wires... ya think you may have crssed a couple of them? Or you have a arcing or bad wire? When your engine misses do you know which cylinder its in?Also you said you rebuilt the pressure regulator..What is your fuel pressure?Sounds more mechanical than it being a sensor....But you never know.. Steve C

Hey Steve.

My timing light is out "on loan".. I'll get it back this week. Regarding the question about the plug wires - they're right. The plug wires were replaced as a potential solution to the miss issue (miss was before new wires)..

We just returned from an afternoon of boating and the truck engine started running terribly - missing, sputtering, coughing.. you name it. We (literally) stumbled home and I noticed the EGR valve didn't return from the highway portion of our trip. I disconnected the vacuum line and it stayed put. It took the exhaust side of my hand vacuum pump to make it close.

I still have the miss, but at least the truck can idle again.

I wonder if the EGR is the root of the problem? If not, it's certainly one of them!

-Steve

Re: 1990 C1500 rough idle/miss Group: alt.autos.4x4.chevy-trucks Date: Sun, Nov 2, 2003, 10:00pm (CST+6) From: snipped-for-privacy@no.com (Tiffany/Steve) Hey Steve. My timing light is out "on loan".. I'll get it back this week. Regarding the question about the plug wires - they're right. The plug wires were replaced as a potential solution to the miss issue (miss was before new wires).. We just returned from an afternoon of boating and the truck engine started running terribly - missing, sputtering, coughing.. you name it. We (literally) stumbled home and I noticed the EGR valve didn't return from the highway portion of our trip. I disconnected the vacuum line and it stayed put. It took the exhaust side of my hand vacuum pump to make it close. I still have the miss, but at least the truck can idle again. I wonder if the EGR is the root of the problem? If not, it's certainly one of them!

-Steve Also when you changed your wires... ya think you may have crssed a couple of them? Or you have a arcing or bad wire? When your engine misses do you know which cylinder its in?Also you said you rebuilt the pressure regulator..What is your fuel pressure?Sounds more mechanical than it being a sensor....But you never know.. Steve C

Sounds like it your EGR could be the problem.. But what about the injectors that are spraying? Have you pulled your fuel rail? Could be as easy as a bad O ring.....Which if your not getting enough fuel to the cylinder at the time will cause a missfire....Which will also cause it to run lean.

take the EGR off and make a block-off plate out of 1/8" plate.......use a gasket for a pattern and cut with a hacksaw, smooth the edges with a grinder, takes about 15 minutes tops

bolt it on and test for a couple days, if that cures it, replace EGR valve

and thank your lucky stars you have a vacuum operated one and not that three-solenoid electrical affair (mucho dollar item)

I disconnected the electrical connection to the solenoid before I left for work this morning. It still misses, but at least there's no valve to stick.

I have a 1971 Corvette laid-up for the winter in the garage.. I'll pull the EGR cover off and try it on the truck.. if I don't just flat-out replace the EGR valve - I *know* it's bad.

Thanks!

-Steve

I know it's "a problem" -- don't know if it's "the problem" though.

I took the TBI off, removed the injectors, replaced the injectors, O-Rings and rebuilt the fuel pressure regulator because it was in front of me. Everything got new seals.

In the process, I cleaned out some carbon on the TBI and made sure the IAC area was clean.

I'm beginning to wonder if the computer is running in a super-rich mode due to the EGR valve..

-Steve