Rather rough idle after new fuel filter.
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Intermediate
Joined: Jul 2019
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Rather rough idle after new fuel filter.
Ok I've been slowly chasing this down. There are days when it kinda rough idles at stop lights. It's not a violent shaking rather more of a strong massage. I'm guessing fuel injectors as they appear original (1992). I just had the fuel filter replaced and now she shakes very rough now even up to about 1500rpm then she settles down. It's worse when I'm idling in gear than just in park. I disabled each of the injectors and it did run rougher than normal (some appeared worse than others), so it's unlikely a spark plug not firing. I closed off each of the main vacuum lines and she still shuddered, making a standard vacuum leak unlikely. I also replaced the spark plug wires last week, hard to say if that helped or not (placebo effect). It's throwing no error codes. I talked to the guy that replaced the filter, I'm going to take it back tomorrow so they can get a good look at it then. We are both wondering if a new filter could be pushing more gas into the system, making the problem more noticeable. It was hitting 40psi last year. Or could the O2 sensors be malfunctions due to that too? Just looking for some guidance where we can really start looking.
Thread Starter
Intermediate
Joined: Jul 2019
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If the injectors are the originals, "ohm them" when they are warm. 1992 is the last year for the problematic Multec injectors that are affected by ethanol in the fuel. I can never remember the exact resistance value, about 14-18 Ohms. Most of them will be about the same, but if you find a single- digit value, that one is bad. Check them all. If you find one or two low resistance, replace them all. That's where I'd begin.
Oh to rule out a few things, I put new spark plug wires last week and ran normally, also I had to replace the ICM and ignition coil last year, so there's a very likely chance those aren't it.
Last edited by DKlettke; May 1, 2020 at 02:06 AM.
Pro
Joined: Dec 2017
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From: Omaha, NE
I had a missing engine at idle on a 92 Vert. It also was dog when I punched it. Mine smelt rich at idle. I had no codes. I checked it with a Tech 2. Didn’t see anything wrong. I took off each injector connector one at a time and noticed that the engine smoothed out with the #8 injector disconnected. I ended up taking it to a shop and they found 2 bad injectors, #8 & #2. That fixed the miss, the rich smell and the running like a dog. Kevin
Team Owner
Joined: Jul 2004
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From: Hartford WI
Sorry forgot to mention that I already did 12.4 to 13, which seems normal. Now there still could be blockage that's preventing them from firing correctly. I did notice that as I took each injector offline there seemed (I can't prove) a roughness difference between each one. Not getting enough fuel through a certain injector I see could cause an imbalance. I'm still eyeing them as the main culprit, but I'm just looking for areas to investigate. I know we need to look at fuel psi as it's running to make sure it stays steady. If not it could be the fuel pump can't handle the new flow. So many things...
Oh to rule out a few things, I put new spark plug wires last week and ran normally, also I had to replace the ICM and ignition coil last year, so there's a very likely chance those aren't it.
Oh to rule out a few things, I put new spark plug wires last week and ran normally, also I had to replace the ICM and ignition coil last year, so there's a very likely chance those aren't it.
Thread Starter
Intermediate
Joined: Jul 2019
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Well update to the story so far... I went back to where I had the new filter installed for a diagnostic. Only thing he could think of was spark plugs were foiled and the rockers were clicking too much and needed to be tuned. They suggested going to a Chevy dealership to get it done, basically where I got her from to begin with. Well their diagnostics over there wasn't much better. They apparently don't have the tools for something that old. Weird. Anyways their recommendation was to replace the injectors and go from there. Which was why I was doing this all to begin with. So it wasn't a complete loss. And yes I'll be ordering the FIC injectors. Their price is very good and since I have to remove the rail I might as well replace the fuel pressure regulator. Kill two birds with one stone.
Safety Car
Joined: Sep 2001
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From: Glenbeulah Wi
I would look at your cap and rotor and make sure the new wires you put on are properly attached. Most rough idke problems are related to spark in my experience. It could be injectors but rule out issues before you start replacing parts.
Thread Starter
Intermediate
Joined: Jul 2019
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What's strange is this suddenly happened after they replaced the fuel filter. We're suspecting that the new filter allows for an increase fuel flow that is accentuating the injector problems. Either that or the plugs are foiled enough to be unable to handle the fuel.
Team Owner
Joined: Jul 2004
Posts: 28,475
Likes: 3,291
From: Hartford WI
Nice theory for a carb car but I would think the ECM will change fueling enough to compensate
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Well I think I found the culprit. Spark plugs. 2,6,8 were foiled. 4 was HORRIBLE, oil deposits. Leaking valve seal?
I haven't done the drivers side yet, doing the passenger side was enough of an adventure for a while. The good news is she's already idling much much smoother than before. And honestly, I didn't find #8 that difficult, helps to be really skinny.
And to be honest, I found removing the plugs so far has been easier than doing the wires, my hands aren't all bloodied up.
Update: Drivers side are done too, 1&3 were easy, 5 was ehh and 7 actually turned out to be the hardest, even 8 was easier. Took her for a test drive and the rough misfire is gone and idles better than before. There is still some shake, but at this point if you weren't paying attention for it, you'd miss it. Now I'm just letting her cool down a tab and see if this has solved the hard hot restart issue to..
One final update: She still has the shake it did before the fuel filter, but it seems to only happen during idling. Next to do project, clean the throttle body. And the rough hot starting is still present, but at least I can remove the sparks and wires from the possible suspects. I will say she accelerates better now and sounds better.
I haven't done the drivers side yet, doing the passenger side was enough of an adventure for a while. The good news is she's already idling much much smoother than before. And honestly, I didn't find #8 that difficult, helps to be really skinny.
And to be honest, I found removing the plugs so far has been easier than doing the wires, my hands aren't all bloodied up.Update: Drivers side are done too, 1&3 were easy, 5 was ehh and 7 actually turned out to be the hardest, even 8 was easier. Took her for a test drive and the rough misfire is gone and idles better than before. There is still some shake, but at this point if you weren't paying attention for it, you'd miss it. Now I'm just letting her cool down a tab and see if this has solved the hard hot restart issue to..
One final update: She still has the shake it did before the fuel filter, but it seems to only happen during idling. Next to do project, clean the throttle body. And the rough hot starting is still present, but at least I can remove the sparks and wires from the possible suspects. I will say she accelerates better now and sounds better.
Last edited by DKlettke; May 4, 2020 at 05:48 PM.