1994 k1500 wild misfire

[name]

Well I got to summit racing, got some parts, the condition is still there :

1) Replaced cap and rotor with the ones that came with the new aftermarket distributor I mentioned earlier = No effect on misfire at idle .

2) Replaced wires with summit brand witch I had good luck with in the past = No effect on misfire at idle .

3) Replaced coil with a summit brand that was listed as a 30,000 volt coil ( witch I figure is probably what the OEM's are ) = No effect on misfire at idle .

4) Cleaned up the old plugs and re gaped them at .035 just to eliminate problems with the new CR43TS and re set timing to 4* BTDC = No effect on misfire at idle .

5) Decided to recheck my work and re clean MAP sensor and EGR solinoid with electrical cleaner, when I took apart the plug from the map sensor I broke them round plastic deviders that surround the terminals, soliderd in a new plug = No effect on misfire at idle .

6) Grabbed a can of WD-40 and just started spraying in every vaccume hose I could find and even down the TBI unit itself, the RPM's kicked up a little and it appeared to smooth out a little, but I did disconnect the battery and I am not sure if it was the result of the WD-40 or the ECM learning where it likes to be .


My questions are :

How long does it take the ECM to settle down and figure what it wants to do after disconnecting the battery ?, It seems like it will work the idle down to 500 rpm in park and about 250 rpm in gear when it is warmed up ( is this to low ? ) There is no drivability issues up to 70 MPH and it seems to like the 4* advance around town , but every time I come to a stop it is fine for about 1-2 minuits and it starts to have a random miss, ( not like it is missing on the same cylinder on every rotation ) the longer I sit at idle the worse and more frequent it gets. once I take off and drive it for a while then stop again it is good for the first 1-2 minuits then starts to act up again.

It is not throwing any SES lite or loging any codes, I did put a timing lite on each plug wire to check for iregular flashes t kinda looks like one of the wires flashes more than the others but I am not 100% sure, I did re rout this wire but doing so did not have any effect on the miss.

Just before I did this tune up I cleaned up the known grounds under rthe dash, frame and inside engine bay area, when I did that I also added a couple of ground wires to firewall to fender and frame to fender, then I started reading another post where they are talking about a " ground loop " What is a ground loop and could this be my problem ?

 

[Schurkey]

5) Decided to recheck my work and re clean MAP sensor and EGR solinoid with electrical cleaner, when I took apart the plug from the map sensor I broke them round plastic deviders that surround the terminals, soliderd in a new plug = No effect on misfire at idle .

MAP or MAF? I have no idea how you'd clean a MAP sensor.

6) Grabbed a can of WD-40 and just started spraying in every vaccume hose I could find and even down the TBI unit itself,

WD-40 is not the right product for that. Aerosol carb cleaner or throttle-body cleaner, would be more reasonable.

How long does it take the ECM to settle down and figure what it wants to do after disconnecting the battery ?

Up to 50 miles of varied driving--in town, highway, etc., is what I've heard. Potentially longer than that if it involves the computer doing OBD2 testing of the various systems. But you don't have OBD2, so the relearn should go relatively fast and easy.

The scan tool will tell you if the fueling is "learned" or not.

It seems like it will work the idle down to 500 rpm in park and about 250 rpm in gear when it is warmed up ( is this to low ? )

WAY too low. Have you ever dicked with the minimum idle speed screw, hidden behind the tamper-resistant cover (at least until someone removes the tamper-resistant cover.)

Does this have the idle vacuum solenoid and vacuum throttle kicker? Does it work?

every time I come to a stop it is fine for about 1-2 minuits and it starts to have a random miss, ( not like it is missing on the same cylinder on every rotation )

How do you know it's not the same cylinder?

the longer I sit at idle the worse and more frequent it gets. once I take off and drive it for a while then stop again it is good for the first 1-2 minuits then starts to act up again.

Connect a scan tool, find out what the sensors are showing after a minute or two of idling.

I started reading another post where they are talking about a " ground loop " What is a ground loop and could this be my problem ?

A ground loop is very unlikely to cause a misfire only after a minute or two of idling.

 

[name]

MAP or MAF? I have no idea how you'd clean a MAP sensor.

MAP Remove MAP sensor, hose down with electrical contact cleaner including the port , let dry and reinstall

WD-40 is not the right product for that. Aerosol carb cleaner or throttle-body cleaner, would be more reasonable.

I used carb cleaner in the beginning but it had no effect, then I read a post saying it was not good to use carb cleaner on the sensors, decided to re do the work with electrical cleaner witch is suppose to be the same as MAF cleaner, used wd-40 to check for vacume leaks because I heard it works for that.

WAY too low. Have you ever dicked with the minimum idle speed screw, hidden behind the tamper-resistant cover (at least until someone removes the tamper-resistant cover.)

Does this have the idle vacuum solenoid and vacuum throttle kicker? Does it work?

This unit did not idle this low before I did the tune up, when I found the broken magnet in the dizzy and and needed to replace it I decided to pull all the stuff that might make me more room to get it in correctly. I am disabled and crawling up on that engine and shimmying my fat *** all the way back there was not something I was looking forward to. I pulled the EGR, MAP sensor and bracket, the coil and the IAC. I replaced the EGR because it was throwing a code, cleaned the MAP sensor as described above and also cleaned the IAC. But when I cleaned the IAC with carb cleaner I started screwing the ram in and out, Not knowing how they really worked or If I messed it up I simply threw in a new one.

After everything was put back together the unit would idle way high and throw an IAC code. After reaserching this new problem I found that the pigtail will fit into the IAC 90* out if the clip is missing and cause a way to high idle condition. After re intsalling the plug the correct way the idle would come down to the above mentiond RPM's witch were a lot closer to where the unit orginally idled at, so I called it good and moved on looking for the soure of my original problem witch was the miss at idle .

I have never messed with the idle speed screw, the cover plate for the adjustment screw is still in place so I figure it has never been touched by a PO either . I have no clue if this unit has a vaccume solenoid or throttle kicker, But there is something mounted in the front of the intake by the thermostate housing that has an electrical connection and a hose that goes to the evap canister. No clue what it is or does though...

How do you know it's not the same cylinder?

If it was the same cylinder, on every rotation, then I should see that on the timming light.

 

[Schurkey]

This unit did not idle this low before I did the tune up... ...I pulled the EGR, MAP sensor and bracket, the coil and the IAC...

...I found that the pigtail will fit into the IAC 90* out if the clip is missing and cause a way to high idle condition. After re intsalling the plug the correct way the idle would come down to the above mentiond RPM's

I'd be looking in the service manual for the proper procedure for replacing the IAC.

One wonders if it's now messed-up due to the connector being installed improperly.

I have never messed with the idle speed screw, the cover plate for the adjustment screw is still in place so I figure it has never been touched by a PO either .

Excellent!

If it was the same cylinder, on every rotation, then I should see that on the timming light.

Not if it's a compression or fuel problem. You might if it was an ignition issue.