Engine running rough
Thread Starter
Racer
Joined: Nov 2002
Posts: 300
Likes: 0
From: Perth WA
Engine running rough
Having problems with my car. 89 L98
On the way home on Saturday the engine started to run a bit rough. So far I have checked/done this
Changed spark plugs.
Checked for spark
Checked Fuel pressure
Checked resistance and voltage at injectors. 1 injector had more resistance than the rest.
Checked for vacuum leaks
Checked for error codes (light hasn't come on)
Finally I changed the fuel filter today. It is a bit better but still not right.
What have I missed?
Any help would be appreciated.
On the way home on Saturday the engine started to run a bit rough. So far I have checked/done this
Changed spark plugs.
Checked for spark
Checked Fuel pressure
Checked resistance and voltage at injectors. 1 injector had more resistance than the rest.
Checked for vacuum leaks
Checked for error codes (light hasn't come on)
Finally I changed the fuel filter today. It is a bit better but still not right.
What have I missed?
Any help would be appreciated.
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
Re: Engine running rough (timallard)
What were the resistance reading on the injectors? Assuming you have the stock Multec injectors, you should have seen about 16 ohms. Let me know what you found! My 89 is currently sick with bad Multec injectors!!!
Thread Starter
Racer
Joined: Nov 2002
Posts: 300
Likes: 0
From: Perth WA
Re: Engine running rough (Sam Lam)
16 ohms yesterday when cold. Just checked again with the engine hot and they are 17 ohms except for No8 which is 3 ohms
Does this mean I have a dud injector?
Does this mean I have a dud injector?
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Thread Starter
Racer
Joined: Nov 2002
Posts: 300
Likes: 0
From: Perth WA
Re: Engine running rough (VetNutJim)
The injector reading 3 ohms is bad.
Does the plenum have to come off to get at the injectors?
I wanted to race the car on Sunday. I don't know if I will have enough time to pull it apart and put it back together by then.
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
Re: Engine running rough (vetteguy216)
Here is what I know about the injectors in a 89 model! Rochester made an injector called Multec and these have a 100% failure rate due to gasoline shorting out the injector coils. These were used in 89 to 91 L98 engines. If you have a reading like "3" ohms, she is shorted and that one is not working! These injectors cannot be reworked and you will not like the cost of new ones! Find some used ones and send them out for cleaning. I will give you a good source for this if you are interested.
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
Re: Engine running rough (vetteguy216)
To check the injectors, remove the connector and place a digitial ohm meter on both connections of the injector. The 89 - 91 injectors should read about 16 ohms. This is an easy and quick check!
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: Engine running rough (Unriced)
You might send Rich some email ...rich@cruzinperformance.com..........h e has reconditioned my injectors (and a lot of forum members) too. He will probably have a replacment for you at a good price. He will also take the time to answer any questions. A real good guy. :yesnod:
Burning Brakes
Joined: Feb 2000
Posts: 824
Likes: 2
From: Camden SC
Re: Engine running rough (Unriced)
Hello there,
The 3 Ohm reading suggests a problem.
Run the car, take a long screw driver, place the screw driver on the injector and "listen" to the screwdriver. Best to do this when no one can see you. I like to use a mechanics stethescope.(spelling). The injector "clicking" should be noticeable. Intermittant or no noise is not good. You can also feel the injector moving but tests like this will disclose a failed injector. Intermittant or dirty ones are more problematic.
You could do a leak down test. Place a fuel pressure gauge on the rail, turn ignition on for about 3-4 seconds, note pressure. Turn key off. Should take several minutes to leak down.
OTC, Kent Moore, and others make an injector pulse tester. You hook this up to the injector, use a fuel pressure gauge, turn the key on, pause, then key off, and activate the injector tester. This will pulse the injector a set number of times. OTC can pulse the injector something like 1, 50, or 500 times, depending on setting. If you compare the suspected bad injector with a suspected good injector, the decrease in pressure noted on the gauge is written down and compared. This is the injector balance test on the vehicle. Bench checks are similar but much more accurate.
Your Ohm reading certainly suggests a bad injector.
Good luck with this repair.
dlmeyers 90 coupe zf6 3 speed shocks
The 3 Ohm reading suggests a problem.
Run the car, take a long screw driver, place the screw driver on the injector and "listen" to the screwdriver. Best to do this when no one can see you. I like to use a mechanics stethescope.(spelling). The injector "clicking" should be noticeable. Intermittant or no noise is not good. You can also feel the injector moving but tests like this will disclose a failed injector. Intermittant or dirty ones are more problematic.
You could do a leak down test. Place a fuel pressure gauge on the rail, turn ignition on for about 3-4 seconds, note pressure. Turn key off. Should take several minutes to leak down.
OTC, Kent Moore, and others make an injector pulse tester. You hook this up to the injector, use a fuel pressure gauge, turn the key on, pause, then key off, and activate the injector tester. This will pulse the injector a set number of times. OTC can pulse the injector something like 1, 50, or 500 times, depending on setting. If you compare the suspected bad injector with a suspected good injector, the decrease in pressure noted on the gauge is written down and compared. This is the injector balance test on the vehicle. Bench checks are similar but much more accurate.
Your Ohm reading certainly suggests a bad injector.
Good luck with this repair.
dlmeyers 90 coupe zf6 3 speed shocks
