Bad running 89
Thread Starter
Le Mans Master
Joined: Dec 2006
Posts: 5,154
Likes: 2
From: Ft Myers Florida
Bad running 89
Any Ideas? Got an 89 auto, runs rough, seems to smooth out at higher rpm but shakes down low.
I have 38-42 lb fuel pressure at the shrader, and she holds pressure after shut off.
All injectors ohm at mid 12 to low 13 hot and cold.
No codes thrown.
Just did a full tune cap rotor wires and plugs still no better.
How can I tell if I have clogged injectors or weak ignition?
I have 38-42 lb fuel pressure at the shrader, and she holds pressure after shut off.
All injectors ohm at mid 12 to low 13 hot and cold.
No codes thrown.
Just did a full tune cap rotor wires and plugs still no better.
How can I tell if I have clogged injectors or weak ignition?
Corvette Enthusiast
Joined: Oct 2007
Posts: 6,797
Likes: 2,719
From: So. Cal.
2025 C7 of the Year Finalist- Unmodified
2024 C7 of the Year Finalist - Unmodified
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Any Ideas? Got an 89 auto, runs rough, seems to smooth out at higher rpm but shakes down low.
I have 38-42 lb fuel pressure at the shrader, and she holds pressure after shut off.
All injectors ohm at mid 12 to low 13 hot and cold.
No codes thrown.
Just did a full tune cap rotor wires and plugs still no better.
How can I tell if I have clogged injectors or weak ignition?
I have 38-42 lb fuel pressure at the shrader, and she holds pressure after shut off.
All injectors ohm at mid 12 to low 13 hot and cold.
No codes thrown.
Just did a full tune cap rotor wires and plugs still no better.
How can I tell if I have clogged injectors or weak ignition?
Burning Brakes
Joined: Jan 2003
Posts: 755
Likes: 32
From: Roswell Georgia
You didn't mention what RPM range smooths out the rough running, or more specifically, what RPM range runs rough. If you're experiencing rough idling below 1200 RPM, it's typically the Idle Air Control (IAC) valve. Remove, clean, or replace. If it's idle to 2500 RPM, it's usually a vacuum leak somewhere. (Check all the vacuum fittings, vacuum lines, snug down the intake bolts, and check for leaks around the throttle body.
BTW, your Ohm readings on the injectors sounds low to me. (I typically expect no less than 14+ Ohms hot.) If they are the original Multecs, check with Jon at FIC for his replacement injectors. Better metering for better mileage and power!
BTW, your Ohm readings on the injectors sounds low to me. (I typically expect no less than 14+ Ohms hot.) If they are the original Multecs, check with Jon at FIC for his replacement injectors. Better metering for better mileage and power!
Thread Starter
Le Mans Master
Joined: Dec 2006
Posts: 5,154
Likes: 2
From: Ft Myers Florida
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
Sometimes, you can destroy a fuel pump in seconds by running out of gas. it may hold pressure, but may not be able to suppy enough volume.
That said, pull your plugs, and do some plug reading.
a rough idle may indicate bad plugs, vacuum leaks, misadjusted throttle body, bad grounds, leaky injectors, timing can be off, poor computer solder joints, bad oxygen sensor,etc.
just for grins,
1. there is a vacuum check valve at the back of the engine for the cruise control. pinch that off, and see if there is a change.
2. pinch off the PCV valve and see if there is a change.
3. pinch off the vacuum line that goes to the charcoal cannister, look for change,
4. loosen and tighten the engine ground at the back of the engine on the right side.
5. disconnect the spark control module located by the heater and see if it is better.
6. pull off the air filter and see if there is a change.
7. make sure the valves are adjusted. one nut tightening itself due to a poor lock can cause a valve to begin hanging open
8. Get creative...... what would you be missing for a smooth idle if you were an L98?
That said, pull your plugs, and do some plug reading.
a rough idle may indicate bad plugs, vacuum leaks, misadjusted throttle body, bad grounds, leaky injectors, timing can be off, poor computer solder joints, bad oxygen sensor,etc.
just for grins,
1. there is a vacuum check valve at the back of the engine for the cruise control. pinch that off, and see if there is a change.
2. pinch off the PCV valve and see if there is a change.
3. pinch off the vacuum line that goes to the charcoal cannister, look for change,
4. loosen and tighten the engine ground at the back of the engine on the right side.
5. disconnect the spark control module located by the heater and see if it is better.
6. pull off the air filter and see if there is a change.
7. make sure the valves are adjusted. one nut tightening itself due to a poor lock can cause a valve to begin hanging open
8. Get creative...... what would you be missing for a smooth idle if you were an L98?
Last edited by coupeguy2001; Aug 15, 2010 at 11:56 AM.
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Thread Starter
Le Mans Master
Joined: Dec 2006
Posts: 5,154
Likes: 2
From: Ft Myers Florida
Supporting Vendor
Joined: Mar 2008
Posts: 1,762
Likes: 14
From: Cumming Ga
not really, usually you will see a few at specs which is 16, all at 12 tells me that they are not the originals. See if they are grey colored.. If they are black someone could have put in lt1 injectors, Lt1 93 up are black and are 12 ohms. But, still they could have mechanical failure. A few clogged would give you those symptoms.
Burning Brakes
Joined: Jun 2008
Posts: 892
Likes: 1
From: New Smyrna Beach Florida
not really, usually you will see a few at specs which is 16, all at 12 tells me that they are not the originals. See if they are grey colored.. If they are black someone could have put in lt1 injectors, Lt1 93 up are black and are 12 ohms. But, still they could have mechanical failure. A few clogged would give you those symptoms.
Jon's the MAN.... call him if you need good advice 
Thread Starter
Le Mans Master
Joined: Dec 2006
Posts: 5,154
Likes: 2
From: Ft Myers Florida
not really, usually you will see a few at specs which is 16, all at 12 tells me that they are not the originals. See if they are grey colored.. If they are black someone could have put in lt1 injectors, Lt1 93 up are black and are 12 ohms. But, still they could have mechanical failure. A few clogged would give you those symptoms.
They are grey.
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
Head that old wives tale. Any idea why it would do that? I mean, if you are out of fuel, the car dies and the pump shuts off. IF it were cooling that causes that to break, isn't the fuel going thru the pump already doing the job? If it can get so hot that it burns, isn't it going to blow up your car if you run low on gas and the fumes ignite in the tank?
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
Not sure I place much value in an Ohm test. After all, it doesn't tell you whether the spray is clogged and the pattern is poor or the volume is consistent between injectors. I will be taking mine out soon for testing. Won't even waste my time doing the Ohm test. I will just send them to FIC and have him tell me what it is doing.
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
Know how many times I have run it down to the end? Wife is tearing out her hair when she sees me fill up the 44 gal Excursion with 46 gallons. I have also run out of gas several times. Never had to replace a pump. Can you think of one logical reason why running out of gas burns up the pump?
Burning Brakes
Joined: Aug 2010
Posts: 833
Likes: 1
I have no idea what causes it, I've seen so many other people's vettes run out of gas and the fuel pump was ruined. It happened to a few of my friends with C4s. I thought that was wrong aswell, until it happened to me.
Team Owner
Joined: Jul 2004
Posts: 28,472
Likes: 3,290
From: Hartford WI
I have never had that happen to me. Only thing I can think of is that the fuel sock got debris in it and it was about time to go. If your fuel sock gets plugged, it won't allow fuel to flow and some tanks have crud in it. As far as burning up, I can't say how it is logical since power shuts down if it can't get fuel and the engine dies..