1989 Corvette Dieseling Issue
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Joined: Feb 2016
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From: Gainesville Georgia
I agree with all you said but I would THINK, and I might be wrong, lets say you are correct, after 1 cycle, the fuel should have ended. Where is the pulse to the injectors coming from and where are they getting fuel unless the pump is running. This is a head scratcher, at least for me.
I know that it comes up rich at startup, at least all my other cars do. It sounds like your idle needs to be adjusted. You can use the FSM method which is pretty easy BUT it makes a lot of assumptions or use IAC counts.
I know that it comes up rich at startup, at least all my other cars do. It sounds like your idle needs to be adjusted. You can use the FSM method which is pretty easy BUT it makes a lot of assumptions or use IAC counts.
Good deal! I think from here, the next thing for me to do is rebuild the gauge cluster, because I've already got my issue with the VSS that I mentioned a while back fixed. It's amazing how a loose connector caused the speedometer, mpg readouts, trip odometer, range, and the shift up light/2nd and 3rd gear lockout feature not to work...
Anyway, once I get the gauge cluster finished, I'll get try setting the base idle using the tachometer readings and see if that fixes it. If that doesn't fix it, then I'll have to bite the bullet and get some ecm data pulled and see what's going on in the computer.
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Even if you get the gauge running, it doesn't mean it is accurate. Even if it is, you don't know if there is anything else wrong like a vacuum leak or the temperature sensor is off. The FSM method assumes stock and everything functions perfect. Kind of why I prefer a scanner.
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this sounds like what my 85 was doing. smelled so rich it would make eyes sting and clothes reak.
i ended up doing the head and intake gasket.
do u think u could have unmetered air getting in? if u have "unmetered air" , ir, air getting in other than past the maf, aka vac leak, (aldl scan info on blm would be good to have) then u might just have the o2's instructing the fuel injectors to put in extra fuel to bring your af ratio back to stoich. you could have a leaking exhaust manifold (i found TWO missing bolts on my driver side exhaust manifold, the side that has the only o2 on an 85) and therefore my o2 was seeing extra air and instructed the injectors to put more fuel in. creating a rich condition.
hope some of that might help.
i ended up doing the head and intake gasket.
do u think u could have unmetered air getting in? if u have "unmetered air" , ir, air getting in other than past the maf, aka vac leak, (aldl scan info on blm would be good to have) then u might just have the o2's instructing the fuel injectors to put in extra fuel to bring your af ratio back to stoich. you could have a leaking exhaust manifold (i found TWO missing bolts on my driver side exhaust manifold, the side that has the only o2 on an 85) and therefore my o2 was seeing extra air and instructed the injectors to put more fuel in. creating a rich condition.
hope some of that might help.
To answer your question aklim, what I was reading was that having too high of an idle speed can cause the engine to have too great of an angular momentum, which will cause the engine to turn just fast enough to sometimes ignite excess fuel in the cylinders because of carbon deposits built up on the piston heads. Having a this supposed rich condition would be where my excess fuel is coming from. So
Replacing the TPS definitely cured my dieseling issue for sure and the car idles at 500 rpm when it's warmed up vs. around like 1,200 rmp before, (with this number being a guess, since at the moment, I can only read up to like 800-900 rpm on the tach). I still haven't pulled any data using a scan tool, so that's probably next on the agenda. Whenever I get that, I'll set the base idle properly and see what other readings it's putting out. As it is now, it's still rich, (I can still smell it, it's especially strong upon startup), and upon cold starting it, it still runs at roughly 500 rmp, but it's really rough, goes up and down, and sometimes, I think it's gonna die.
Replacing the TPS definitely cured my dieseling issue for sure and the car idles at 500 rpm when it's warmed up vs. around like 1,200 rmp before, (with this number being a guess, since at the moment, I can only read up to like 800-900 rpm on the tach). I still haven't pulled any data using a scan tool, so that's probably next on the agenda. Whenever I get that, I'll set the base idle properly and see what other readings it's putting out. As it is now, it's still rich, (I can still smell it, it's especially strong upon startup), and upon cold starting it, it still runs at roughly 500 rmp, but it's really rough, goes up and down, and sometimes, I think it's gonna die.
Last edited by VikingTrad3r; Apr 20, 2016 at 06:39 PM.
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Joined: Feb 2016
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From: Gainesville Georgia
Even if you get the gauge running, it doesn't mean it is accurate. Even if it is, you don't know if there is anything else wrong like a vacuum leak or the temperature sensor is off. The FSM method assumes stock and everything functions perfect. Kind of why I prefer a scanner.
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Joined: Feb 2016
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From: Gainesville Georgia
this sounds like what my 85 was doing. smelled so rich it would make eyes sting and clothes reak.
i ended up doing the head and intake gasket.
do u think u could have unmetered air getting in? if u have "unmetered air" , ir, air getting in other than past the maf, aka vac leak, (aldl scan info on blm would be good to have) then u might just have the o2's instructing the fuel injectors to put in extra fuel to bring your af ratio back to stoich. you could have a leaking exhaust manifold (i found TWO missing bolts on my driver side exhaust manifold, the side that has the only o2 on an 85) and therefore my o2 was seeing extra air and instructed the injectors to put more fuel in. creating a rich condition.
hope some of that might help.
i ended up doing the head and intake gasket.
do u think u could have unmetered air getting in? if u have "unmetered air" , ir, air getting in other than past the maf, aka vac leak, (aldl scan info on blm would be good to have) then u might just have the o2's instructing the fuel injectors to put in extra fuel to bring your af ratio back to stoich. you could have a leaking exhaust manifold (i found TWO missing bolts on my driver side exhaust manifold, the side that has the only o2 on an 85) and therefore my o2 was seeing extra air and instructed the injectors to put more fuel in. creating a rich condition.
hope some of that might help.
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I may actually have found a vacuum leak on the car. There's a small bit of vacuum tubing that's actually cracked into 3 or 4 pieces. I keep forgetting that's there because I have it all taped together. Chances are though that there's still somewhat of a leak. I'll try replacing that tubing later and we'll see if that makes a difference.
Last edited by antfarmer2; Apr 21, 2016 at 09:09 AM.
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From: Gainesville Georgia
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great , is it vac tubing? sometimes a simple piecd of rubber tubing can serve as a bridge with clamps on each side.
check to see if u have all exhaust bolts in themanifold.
check to see if u have all exhaust bolts in themanifold.
Well, let me re-phrase it. It was something I know needs to be fixed, but I keep putting it off, because while it's rich, it runs a lot better than it used to, and I've been driving it as it is for a while. It was taped up when I bought the car, and I re-taped it as a temporary fix. However, I do know that base idle isn't set properly, because I adjusted the screw to get the idle better, (by ear). So both the replacement of the vacuum tubing, and setting the base idle correctly have to be done then.
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From: Gainesville Georgia
Yes, it is Vacuum Tubing. I'll check to see if the bolts in the exhaust manifold are present.
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I've got news everyone, I successfully restored the gauge cluster and it works as good as new! So glad that the solid hour or two removing 27 year old adhesive from the LCDs was worthwhile! 
I will attempt to set the base idle with the rpms later today hopefully, as well as replace the vacuum tubing, and see what that does. Whenever I finally get access to an OBD 1 scanner/software, I'll set it using the IAC counts. I'll post what happens later.
I will attempt to set the base idle with the rpms later today hopefully, as well as replace the vacuum tubing, and see what that does. Whenever I finally get access to an OBD 1 scanner/software, I'll set it using the IAC counts. I'll post what happens later.
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I've got news everyone, I successfully restored the gauge cluster and it works as good as new! So glad that the solid hour or two removing 27 year old adhesive from the LCDs was worthwhile! I will attempt to set the base idle with the rpms later today hopefully, as well as replace the vacuum tubing, and see what that does. Whenever I finally get access to an OBD 1 scanner/software, I'll set it using the IAC counts. I'll post what happens later.
I will attempt to set the base idle with the rpms later today hopefully, as well as replace the vacuum tubing, and see what that does. Whenever I finally get access to an OBD 1 scanner/software, I'll set it using the IAC counts. I'll post what happens later.
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get an aldl cable and then check out the scan/tune section and search it and u should be good to go.
i ordered my cable from aldlcable.com i think
I've got news everyone, I successfully restored the gauge cluster and it works as good as new! So glad that the solid hour or two removing 27 year old adhesive from the LCDs was worthwhile! I will attempt to set the base idle with the rpms later today hopefully, as well as replace the vacuum tubing, and see what that does. Whenever I finally get access to an OBD 1 scanner/software, I'll set it using the IAC counts. I'll post what happens later.
I will attempt to set the base idle with the rpms later today hopefully, as well as replace the vacuum tubing, and see what that does. Whenever I finally get access to an OBD 1 scanner/software, I'll set it using the IAC counts. I'll post what happens later.
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From: Gainesville Georgia
Ok, so setting the base idle according to a guide on this forum ended up making it run worse...
I'm guessing it's because I didn't disconnect the EST, so it tried to compensate by changing the timing for me when I didn't need that to happen. It's now more rich than before. On the bright side, still no dieseling though
Does disconnecting the EST make a difference? I still don't have access to an ALDL cable, but I'll try to order one soon.
I'm guessing it's because I didn't disconnect the EST, so it tried to compensate by changing the timing for me when I didn't need that to happen. It's now more rich than before. On the bright side, still no dieseling though
Does disconnecting the EST make a difference? I still don't have access to an ALDL cable, but I'll try to order one soon.
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From: Gainesville Georgia
I see what you mean. I guess I'll have to go by the FSM, and then tweak it until it runs a little bit better for now.
Last edited by jhend1000; Apr 26, 2016 at 02:47 PM.
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From: Gainesville Georgia
I've checked a lot of places, so far O'Reilly Auto Parts is the only place that sells an OBD1 scanner, but it's over $300. Everywhere I've been so far has told me that they can't scan OBD1 data, like they can for OBD2.
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Don't they loan tools? You can do that in the parking lot if needs be.
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