92 idling funny

[scotts62]

I have a 92 x cab Chevy 350/4l60 that i have basically completely gone through, new engine, trans, drive line and rear end and even ripped out the interior to clean it up and swap the dash to a better looking one (got the truck dirt cheap). My deal is is that when its idling it clearly has a miss to it but when you put it in gear it goes away but if you let it sit there for a min or so, about every 10-15 seconds it has a miss.. I have checked the compression and its perfect, hooked a vacuum gauge to it to see if by chance i got a valve too tight but the needle is dead set still and not jumping around, i did have the ignition module go out of it a few weeks ago and figured since that went out that maybe by chance it could be getting weak even though i have heard that they either work or they dont. And the thing runs fine driving around town or wherever.

It doesnt have an engine light or anything nor has any codes..

If anyone has any ideas im listening

Here is a pic for grins.

[ChevLoRay]

Aggravating, ain't it?

I had a '78 Datsun pickup that had one of those irregular idles and I was not comfortable working on the carburetor that I didn't have any understanding about.

But, we don't have a carburetor on your truck, do we? So, that ain't what it is, but I wonder if it could be fuel-related, without knowing what in particular it might be. What do these TBI trucks have for an idle circuit? That's the only thing that comes to my (damaged) brain.

[scotts62]

yes it is.

No its a tbi setup, i did check the fuel pressure at idle and reving it up slow and it held 13psi consistently. My guess is something electrical giving me fits but i figured i would post it up and see if someone else has ran across this type of ghost

[ChevyTech]

Do you know what the ethanol content is in the fuel you are buying?

Many TBI trucks get a strange rhythmic misfire or stumble at idle when the fuel has ethanol in it. The higher the ethanol content, the more noticeable it is.

The dealership bought a test kit/beaker for testing the ethanol content of fuel samples and we found different ethanol content levels from various local gas stations.

You may want to try buying gasoline somewhere else and see if it helps.

Another thing you should check is:
On these distributors the housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues.

[scotts62]

Originally Posted by ChevyTech

Do you know what the ethanol content is in the fuel you are buying?

Many TBI trucks get a strange rhythmic misfire or stumble at idle when the fuel has ethanol in it. The higher the ethanol content, the more noticeable it is.

The dealership bought a test kit/beaker for testing the ethanol content of fuel samples and we found different ethanol content levels from various local gas stations.

You may want to try buying gasoline somewhere else and see if it helps.

Another thing you should check is:
On these distributors the housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues.

I have never bought the ethanol fuel since i have had the truck its been only 100% gas, even a higher octane, i try and stay away from that crap

Ill have to take the distributor out and check that to see, Thanks!

[ChevyTech]

Originally Posted by scotts62

I have never bought the ethanol fuel since i have had the truck its been only 100% gas, even a higher octane, i try and stay away from that crap

Ill have to take the distributor out and check that to see, Thanks!

Ethanol is mandated by law where I live.

The TBI 350s have a 9 to 1 compression ratio.
The TBI 305s have smaller combustion chamber heads with a slightly higher 9.3 to 1 compression ratio.

I have found the 305s will run best on the 89 octane rather then the 87 octane here where we must use an ethanol blend all year.

When the distributor is worn, it can be felt by removing the cap and wiggling the shaft sideways. You don’t need to pull it to check this. I have run across a few that have extreme up and down play also.

[scotts62]

Originally Posted by ChevyTech

Ethanol is mandated by law where I live.

The TBI 350s have a 9 to 1 compression ratio.
The TBI 305s have smaller combustion chamber heads with a slightly higher 9.3 to 1 compression ratio.

I have found the 305s will run best on the 89 octane rather then the 87 octane here where we must use an ethanol blend all year.

When the distributor is worn, it can be felt by removing the cap and wiggling the shaft sideways. You don’t need to pull it to check this. I have run across a few that have extreme up and down play also.

Oh wow so there is no way around buying good gas for you is there..?

This one is 0.40 over with stock type speed pro pistons in it but its probably around 9.something, nothing fancy.

Ill try and check that out tonight, i kind of hop it is it but then again not because those distributors arnt too cheap, at least my last dealings with them..

[ChevLoRay]

Ethanol is in the fuel I buy. I buy it from Murphy's (WalMart). I buy gas from Kroger (don't know who the mfr is) and I buy it from Exxon (the sign of the double-cross!!). Each pump has a sticker that says it either "contains up to 10% ethanol" or "contains 10% ethanol".

Doesn't matter if it is 87RON or 93RON. I do think that when I two my popup, I'm gonna go with the 93 octane and see if it will let me tow without setting the code that I got a couple weeks ago.

[scotts62]

We have a Valero(better gas) and a Loves store(not so good gas) across from each other and in my wifes car she gets 17mpg from the shell and 24mpg with the valero just around town driving, on the hwy its around 30mpg, so its a pretty big difference in gas around here.

[lurch115]

have you pulled the Idle Air Control valve out to see if maybe its carboned up. my uncle's '92 was giving him fits so we pulled the IAC valve, cleaned it, and reinstalled. sure enough that was the cause of several issues with idle and just off idle conditions.

[scotts62]

Originally Posted by lurch115

have you pulled the Idle Air Control valve out to see if maybe its carboned up. my uncle's '92 was giving him fits so we pulled the IAC valve, cleaned it, and reinstalled. sure enough that was the cause of several issues with idle and just off idle conditions.

Yeah i took the whole throttle body apart when i built the engine and cleaned everything, it idles better in gear but you can feel it slightly still. Ill check it again just to be sure though, thanks.

[scotts62]

About to go check the distributor now but figured i would post up what it was doing today. I started it up a few mins before i left work to let it warm up and it idles at 800 rpm then drops down to 400 then 1000 then to 800 for a few seconds then repeats a couple times and died once but only does it until it warms up then it just has the miss and not the funky rpm thing. But anyways im going to see if the dizzy is sloppy and worn out now..


EDIT----- I took the cap off and it has some movement in it but how much is too much? My guess is .010 to .015

[70BLAZERX2]

This is a very common problem on TBI motors..You need to change your dist. And i bet the problem goes away..I work on taxi cabs..91-93 caprices and they all have over 500,000 miles on them...still on the road..I keep distributor on the shelf.

Originally Posted by ChevyTech

Another thing you should check is:
On these distributors the housing/upper bushing area gets so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues.

[scotts62]

Originally Posted by 70BLAZERX2

This is a very common problem on TBI motors..You need to change your dist. And i bet the problem goes away..I work on taxi cabs..91-93 caprices and they all have over 500,000 miles on them...still on the road..I keep distributor on the shelf.

Im just trying to make sure it is it before i throw $150 bucks at it, if it is suppose to have that much movement then i guess its good but if not ill have to get one..

[SiCk_DiAbLo]

Originally Posted by scotts62

I have a 92 x cab Chevy 350/4l60 that i have basically completely gone through, new engine, trans, drive line and rear end and even ripped out the interior to clean it up and swap the dash to a better looking one (got the truck dirt cheap). My deal is is that when its idling it clearly has a miss to it but when you put it in gear it goes away but if you let it sit there for a min or so, about every 10-15 seconds it has a miss.. I have checked the compression and its perfect, hooked a vacuum gauge to it to see if by chance i got a valve too tight but the needle is dead set still and not jumping around, i did have the ignition module go out of it a few weeks ago and figured since that went out that maybe by chance it could be getting weak even though i have heard that they either work or they dont. And the thing runs fine driving around town or wherever.

It doesnt have an engine light or anything nor has any codes..

If anyone has any ideas im listening

Here is a pic for grins.

What's the canister on the left of the breather that attaches to the fender, I never really knew what that was..

[scotts62]

Just part of the breather, there isnt anything special inside or anything though..

[TennesseeZ]

Those trucks have an air intake from the grille area/radiator core support that snakes it's way thru the fender to that tube, factory version of a "fresh air", or "cold air" intake I suppose, that particular piece contains a kind of inverted cone inside they call a silencer. Some people consider it restrictive and remove the cone. Not real real hard to do with a hacksaw blade, not sure of the benefits tho. The system is pretty restrictive before it ever gets to that point.

[scotts62]

Yeah seems like a cheesy way to run the ducting to have it get air but it works i guess, ive been wanting to change it all together but ill leave it for now, i have other problems

[ChevyTech]

You should not be able to feel sideways movement of the distributor shaft with your hand.

It does not take a lot of movement to cause problems. You should get a distributor.

I bought a TBI distributor at the local U-Pull-It for $25 that was in very good condition.

A common cause of an idle that hunts up and down on these trucks is a lean fuel mixture, usually from low fuel pressure, but you said you have good pressure. The fuel pressure must be tested with the engine running. An IAC sticking and a worn distributor can also cause idle issues.


Note:
When you replace, remove and cleaned an IAC, or unplugged the IAC with the key on, the ECM may need to relearn the IAC position. This will not happen without driving the truck and meeting specific conditions or taking other steps the cause it to relearn the idle.

[ChevLoRay]

When ChevyTech "speaks" I pay attention, because I learn from him. Thanks for teaching us and guiding us through some tough issues.

[scotts62]

Originally Posted by ChevyTech

You should not be able to feel sideways movement of the distributor shaft with your hand.

It does not take a lot of movement to cause problems. You should get a distributor.

I bought a TBI distributor at the local U-Pull-It for $25 that was in very good condition.

A common cause of an idle that hunts up and down on these trucks is a lean fuel mixture, usually from low fuel pressure, but you said you have good pressure. The fuel pressure must be tested with the engine running. An IAC sticking and a worn distributor can also cause idle issues.


Note:
When you replace, remove and cleaned an IAC, or unplugged the IAC with the key on, the ECM may need to relearn the IAC position. This will not happen without driving the truck and meeting specific conditions or taking other steps the cause it to relearn the idle.

Ok Thanks i appreciate it, i checked one i had from a v6 and it hardly moved at all so that kinda told me that mine was in fact in bad shape. I will try and hit the local pull a part this weekend and hope it cures the bug.

[k5hart]

I'm also putting my vote in for the distributor. Check the parts stores. I don't remember paying that much for mine last year.

[ChevyTech]

Thank you for the vote of confidence ChevyLoRay.

Scotts62 take a look at how little clearance there is between the shaft reluctor tips, and the points on the pole piece for the pickup coil, when you get your replacement distributor. These distributors can also have a problem maintain their magnetism and the parts hitting against each other has to hurt the magnetism.

[scotts62]

I looked at they one that is in it and the points are shiny so it is hitting. I pulled the 454 out of my crew cab last night and checked out the distributor on it and am going to use it for now since its in WAY better shape but im just wondering why it looks different around the pickup coil area, its different around where the reluctor points are and more bulkier, now im sure it will work but was just wondering why they are different? Is this one a replacement from the same thing happening before? ill get a pic later to better explain what im talking about.

[ChevyTech]

I don’t know if the big block distributor is the same or not. I have not worked on a big block in years. We just don’t see many of them where I am. Most of the trucks in this area are used like a family car.