Fuel Injector Confusion
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Fuel Injector Confusion
I was just out driving my '86 Roadster, and when I made a turn and went to accelerate the car started to shudder. 
Limped it home, and I'm now checking everything over.
I'm thinking one of two things -- injectors or motor mount. When at idle, the shudder seems almost non-existant. But around 1800RPMS it becomes real noticable. I have "tested" the injectors, but the process doesn't make much sense to me.
I disconnect the lead from the injector and test the impediance. My readings are jumping all over the place -- on the potential bad injector and one that seems to be working fine. Is this normal??
The other thing is, I don't understand how pulling the leads and testing the lead to the injector tells me how I have a bad injector. Thoughts?
Limped it home, and I'm now checking everything over. I'm thinking one of two things -- injectors or motor mount. When at idle, the shudder seems almost non-existant. But around 1800RPMS it becomes real noticable. I have "tested" the injectors, but the process doesn't make much sense to me.
I disconnect the lead from the injector and test the impediance. My readings are jumping all over the place -- on the potential bad injector and one that seems to be working fine. Is this normal??
The other thing is, I don't understand how pulling the leads and testing the lead to the injector tells me how I have a bad injector. Thoughts?
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
The ohmmeter is used to check resistance of the injector coil across the two pins of the injector. An ohmmeter is never used on a live circuit. With power disconnected an ohmmeter could be used on the leads to check for a short to ground.
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Ok, just checked all my injectors, and they've checked out fine. Not sure what to do now. It's like when I made the turn, something came loose and its a strong shudder. At idle, it's barely noticable. The more throttle that is given, the more pronounced it becomes.
Pro
Joined: May 2002
Posts: 541
Likes: 2
From: Kalama WA
Does it happen when car is not moving?? Sounds more like a rear end /half shaft axle u joint issue. Check and eliminate items systematically. If it happens at a stop- investigate and probably an engine issue- fuel/ignition, etc. If it shows up while rolling- check the whole drivetrain. If it is a motor mount- open the hood, start it up and slowly let out the clutch or auto put in drive. You will see that motor try to jump out of the engine bay. It will be obvious.
Last edited by kize; May 27, 2007 at 11:26 PM.
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Yes, it happens when the car is not moving and when it is moving. The more engine speed there is, the more significant it is. The fact that it just suddenly starting doing it has me thinking something drivetrain came loose. Hope the tranny and rear end are OK, U-joints I can live with..
Pro
Joined: May 2002
Posts: 541
Likes: 2
From: Kalama WA
Shudder or vibration?. You might want to check your harmonic balancer also. Mine came loose and spun on the hub. Made a hell of a vibration. The only way I found it was putting a timing light on it. It was about 40 degrees off on timing and still ran great. Just had on heck of a vibration and got worse the higher the rpm. Just a thought.
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
You say the shudder/vibration is there even if not moving, if it is there with the engine running and the transmission in neutral you can safely rule out transmission and rear axle.
Kize had a good suggestion that is easy to check with a timing light, if your base timing is way off, take a hard look at the damper. Along the same line I would check the other easy simple things first, a spark plug wire could have come off when making the turn, you may also want to check the fuel pressure, you could have disturbed sediment in the tank that partially plugged the fuel filter.
Did you inspect the motor mounts that you suspected initially?
Kize had a good suggestion that is easy to check with a timing light, if your base timing is way off, take a hard look at the damper. Along the same line I would check the other easy simple things first, a spark plug wire could have come off when making the turn, you may also want to check the fuel pressure, you could have disturbed sediment in the tank that partially plugged the fuel filter.
Did you inspect the motor mounts that you suspected initially?
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Hows the cap and the rotor looking?
Check and test the ignition coil and also the ignition control module.
Check all the wires to make sure they are not burned or shorting on something.
Does it do this hot or cold or both?
Just cause your injectors ohm tested good doesnt mean they are all firing or getting the signal to fire.
Check that the torque converter is bolted up to the flex plate nice and tight.
Check the compression and also CO test the coolant.
Check and test the ignition coil and also the ignition control module.
Check all the wires to make sure they are not burned or shorting on something.
Does it do this hot or cold or both?
Just cause your injectors ohm tested good doesnt mean they are all firing or getting the signal to fire.
Check that the torque converter is bolted up to the flex plate nice and tight.
Check the compression and also CO test the coolant.
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Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Ive got a smooth running Buick 3800 V6 here if you want some weight reduction.....
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
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From: E. Amherst NY
OK, results thus far.
Injector Resistance, range from 16.9 to 17.8 ohms
Fuel Pressure with only ignition on, 46psi, then falls - Will check that out.
Plug wires are tight and connected
Added drygas last night -- I did just fill the tank about 20 miles before it happened. Potential bad gas?
Coolant level OK
Oil OK
Transmission Fluid OK
Distributor is tight
Timing is the same as it was when I set it 1500 miles ago.
So, thus far. I need to investigate the fuel pressure. The car is much smoother in neutral than it is in drive, but it still shudders nonetheless.
Injector Resistance, range from 16.9 to 17.8 ohms
Fuel Pressure with only ignition on, 46psi, then falls - Will check that out.
Plug wires are tight and connected
Added drygas last night -- I did just fill the tank about 20 miles before it happened. Potential bad gas?
Coolant level OK
Oil OK
Transmission Fluid OK
Distributor is tight
Timing is the same as it was when I set it 1500 miles ago.
So, thus far. I need to investigate the fuel pressure. The car is much smoother in neutral than it is in drive, but it still shudders nonetheless.
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Could be, but i dont know, its hard to say what it could be without being there to see it, cause you say it happened all of a sudden really, you could have a look in the tank and see what it looks like on the bottom, the sock filter mightve picked up a chuck, pump might be on its way out, regulator could be leaking internally, etc etc...
Thread Starter
Le Mans Master
Joined: Mar 2006
Posts: 5,262
Likes: 0
From: E. Amherst NY
I have a shot plug wire. Replaced it -- after I had pulled the shield over the torque converter and the flywheel. Now I can't get the shield to go back without hitting the flywheel. I feel pretty confident it was the plug wire though.
Safety Car
Joined: Jun 2006
Posts: 3,629
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From: FL
