Hello all... I need to tap the knowledge of the board here with couple of what I thought were stupid little problems on my 97 LC, that appear to be painting a pretty grim picture here...
First of all... my truck has been suffering from a slightly rough idle for about a year now. Everything originally started with a CEL on a long road trip that turned out to be an EGR vsv. Replaced VSV and the modulator at the same time and haven't seen the CEL since (10k ago). When I did the EGR mod I also went though and did a complete tune up including plugs/cap/rotor/wires. After everything was done I was left with a VERY mild roughness, just a slight vibration through the steering wheel at stop while in D, and a slight seat of the pants vibration. Checked the intake tube 3 times, nothing. Went through 2 stealerships and an idependent that couldn't find anything wrong with it, telling me I'm nuts in a round about way. I decided to let it go and watch it for a bit. Then last week I read this thread by desmocruiser...
And it appears that his symptoms are very similar to mine. As the truck drops to idle, it will drop to ~700, and then drop ~20 rpm's every couple of seconds to ~600 where it settles out. When it hits 600 the idle gets slightly rough... sometimes rougher than others. Very occasionally quite rough. None of the cylinders seem to be completely missing as the load balance test as per Robbie shows further deterioration of the idle will each six plugs being removed.
After reading desmocruisers ordeal, it is starting to look like this may be a partial fault on one of the injector wires.
Now on to the second part of my problem... Last week I left my truck parked at a friends house, nose in against a block wall. When I came down to get it in the morning and started it up, I could hear a knocking sound reflecting off the wall so I popped the hood. It's hard to describe the sound because it does not sound like a rod or bottom end knock exactly. And I have a friend that has a Chevy Shakerado and it does not sound like the piston slap that he has either. The closest description that I can come up with is the sound of bubbles going through a high pressure hydraulic piston pump. Higher pitched than any knock or diesel-like clatter. Like two marbles or rocks hitting together. It can be heard from the top and the bottom... slightly louder from underneath the truck. Very intermittent, for only the first minute or two after startup after the truck has sat overnight, and I only hear about 10-12 knocks before it stops. They are not at any regular interval either. It's been very dificult trying to localize it with a stethescope since I have to try to remember how loud it was yesterday since I cannot get all the way around the truck in one go before it stops.
This problem may have been going on for a little while as the knock cannot be heard from inside the truck, and I never park overnight near anything that would reflect the knock into the truck.
What are the odds that these two problems may be related?!?
The rough idle may(likely) be a lean condition at idle in one/all of the cyclinders due to a partial wiring fault/fuel pump/injectors. I don't think that it is a fuel pump because I don't have any detonation issues. I have had the injectors cleaned, on the truck with cleaner right into the rail and have run a couple of cans of redline through it since.
And yes... the headgasket is running around in the back of my mind as well. Need to try the bubble test again today... 4500 rpm's for 5 minutes was it??
The truck was dealer maintained with records when I got her at 90K, and has had Mobil1 ever since. Any knocking/slap would not be from poor maintanance.
I'm not even sure where to start looking here. Wire looms... intake tube again... sensor checks/adjustment as per FSM. Can there be wiring damage without any visible breaks in the wire... if so how do I check/verify the wiring if it 'appears' OK. This is where ayou guys come in... what are the most likely culprits here.
Lastly... letting what seemed to be a stupid little rough idle condition go... what kind of damage could have been done to the engine causing the knock, if that is what it is. Is this where I should hit myself in the head with a metric wrench for having more pressing things to deal with recently...
Waiting with tools in hand...
Chris
First of all... my truck has been suffering from a slightly rough idle for about a year now. Everything originally started with a CEL on a long road trip that turned out to be an EGR vsv. Replaced VSV and the modulator at the same time and haven't seen the CEL since (10k ago). When I did the EGR mod I also went though and did a complete tune up including plugs/cap/rotor/wires. After everything was done I was left with a VERY mild roughness, just a slight vibration through the steering wheel at stop while in D, and a slight seat of the pants vibration. Checked the intake tube 3 times, nothing. Went through 2 stealerships and an idependent that couldn't find anything wrong with it, telling me I'm nuts in a round about way. I decided to let it go and watch it for a bit. Then last week I read this thread by desmocruiser...
desmocruiser said:
And it appears that his symptoms are very similar to mine. As the truck drops to idle, it will drop to ~700, and then drop ~20 rpm's every couple of seconds to ~600 where it settles out. When it hits 600 the idle gets slightly rough... sometimes rougher than others. Very occasionally quite rough. None of the cylinders seem to be completely missing as the load balance test as per Robbie shows further deterioration of the idle will each six plugs being removed.
After reading desmocruisers ordeal, it is starting to look like this may be a partial fault on one of the injector wires.
Now on to the second part of my problem... Last week I left my truck parked at a friends house, nose in against a block wall. When I came down to get it in the morning and started it up, I could hear a knocking sound reflecting off the wall so I popped the hood. It's hard to describe the sound because it does not sound like a rod or bottom end knock exactly. And I have a friend that has a Chevy Shakerado and it does not sound like the piston slap that he has either. The closest description that I can come up with is the sound of bubbles going through a high pressure hydraulic piston pump. Higher pitched than any knock or diesel-like clatter. Like two marbles or rocks hitting together. It can be heard from the top and the bottom... slightly louder from underneath the truck. Very intermittent, for only the first minute or two after startup after the truck has sat overnight, and I only hear about 10-12 knocks before it stops. They are not at any regular interval either. It's been very dificult trying to localize it with a stethescope since I have to try to remember how loud it was yesterday since I cannot get all the way around the truck in one go before it stops.
This problem may have been going on for a little while as the knock cannot be heard from inside the truck, and I never park overnight near anything that would reflect the knock into the truck.
What are the odds that these two problems may be related?!?
The rough idle may(likely) be a lean condition at idle in one/all of the cyclinders due to a partial wiring fault/fuel pump/injectors. I don't think that it is a fuel pump because I don't have any detonation issues. I have had the injectors cleaned, on the truck with cleaner right into the rail and have run a couple of cans of redline through it since.
And yes... the headgasket is running around in the back of my mind as well. Need to try the bubble test again today... 4500 rpm's for 5 minutes was it??
The truck was dealer maintained with records when I got her at 90K, and has had Mobil1 ever since. Any knocking/slap would not be from poor maintanance.
I'm not even sure where to start looking here. Wire looms... intake tube again... sensor checks/adjustment as per FSM. Can there be wiring damage without any visible breaks in the wire... if so how do I check/verify the wiring if it 'appears' OK. This is where ayou guys come in... what are the most likely culprits here.
Lastly... letting what seemed to be a stupid little rough idle condition go... what kind of damage could have been done to the engine causing the knock, if that is what it is. Is this where I should hit myself in the head with a metric wrench for having more pressing things to deal with recently...
Waiting with tools in hand...
Chris
