Developed a miss today.

[Z06scentair]

Took the car out this morning was running fine. Then about five miles later it began to miss at idle. You can hear the dual mass rattling. It appears to miss under load key on and off?

No DTC codes on a 12

The injectors were changed last year. I swaped plugs out two weeks ago with denso iridiums.

Original coils, wires, and fuel pumps to my knowledge.

With the key on the FP is 47 psi, after the key is shut off it dropped to 43 about ten minutes.

With the car running it shows 45 psi.

Any thoughts?

[Dynomite]

Just for starters

Did it run fine after you changed plugs? I assume so.
Since that is the last item you changed, maybe check plugs (are they tight) and wire boots one more time.

Could be a wire short/failure since you moved wires around when changing plugs.
You might also pull a plug and see what it looks like.

[Z06scentair]

Originally Posted by Dynomite

Did it run fine after you changed plugs? I assume so.
Since that is the last item you changed, maybe check plugs (are they tight) and wire boots one more time.

Could be a wire short/failure since you moved wires around when changing plugs.
You might also pull a plug and see what it looks like.

I suspect wires too....as the number 7 is oil soaked from the cam cover o ring failure.

The car ran fine the last few times I drove it, about fifty miles altogether.

I just pulled the fuel sending unit....should I go ahead and replace the pumps since there out?

Does the posted above fuel pressures look acceptable?

[Paul Workman]

Originally Posted by Z06scentair

Took the car out this morning was running fine. Then about five miles later it began to miss at idle. You can hear the dual mass rattling. It appears to miss under load key on and off?

No DTC codes on a 12

The injectors were changed last year. I swaped plugs out two weeks ago with denso iridiums.

Original coils, wires, and fuel pumps to my knowledge.

With the key on the FP is 47 psi, after the key is shut off it dropped to 43 about ten minutes.

With the car running it shows 45 psi.

Any thoughts?

Some more info?

1. Were the injectors new or "rebuilt"?
2. Is it only one cylinder or two, and which one/ones?
3. Plug heat range? (for reference, the AC/Delco 41-602s are a good place to start. Deviating far from there would require some special circumstances, methinks)
4. Did the car idle for a long time? (I.e., fouling the plugs)
5. Did you pull the plugs yet, and if so what do they look like?

I understand no DIC but are you saying the ALDL test returns a "12" code?

Fuel pressure looks about normal, Leak-down fuel pressure is a tad more than I have experienced, but I don't think that you have a leak issue to be concerned with...unless there is one cylinder getting flooded, I suppose. (others will have to add focus to this).

P.

[Z06scentair]

Originally Posted by Paul Workman

Some more info?

1. Were the injectors new or "rebuilt"?
   
   new
2. Is it only one cylinder or two, and which one/ones?
   
   not sure
   
3. Plug heat range? (for reference, the AC/Delco 41-602s are a good place to start. Deviating far from there would require some special circumstances, methinks)
   
   deviated one heat range colder as that was the only available Denso plug number 20 maybe?
   
4. Did the car idle for a long time? (I.e., fouling the plugs)

car ran fine for 20 miles and was filled with fuel then straight home

[Z06scentair]

So should I put the fuel pump assembly back in the car? Or just replace the pumps since I have it out? They are 24 years young now, with little exercise over the years 19k miles.

[Paul Workman]

Originally Posted by Z06scentair

So should I put the fuel pump assembly back in the car? Or just replace the pumps since I have it out? They are 24 years young now, with little exercise over the years 19k miles.

Well, that's your call. I'm of the opinion that if it ain't broke, don't fix it! I've had cases of "infant mortality" where chit dies right out of the box. That can really throw a curve into the troubleshooting process. (But, if you do replace them, be sure to verify they're both working - by taking a drive and monitoring fuel pressure under normal driving (closed loop) and WOT (open loop). Closed loop pressure to be between 43-48 ish. WOT pressure should be in the 52-53 ± a pound or two. And, should the dynamic pressure be on the low side, I'd suggest changing the in-line filter (behind the right front wheel, next to the frame)).

[Z06scentair]

Originally Posted by Paul Workman

Well, that's your call. I'm of the opinion that if it ain't broke, don't fix it! I've had cases of "infant mortality" where chit dies right out of the box. That can really throw a curve into the troubleshooting process. (But, if you do replace them, be sure to verify they're both working - by taking a drive and monitoring fuel pressure under normal driving (closed loop) and WOT (open loop). Closed loop pressure to be between 43-48 ish. WOT pressure should be in the 52-53 ± a pound or two. And, should the dynamic pressure be on the low side, I'd suggest changing the in-line filter (behind the right front wheel, next to the frame)).

Paul

Thanks for jumping in.

Im going to put the pumps back in and take a drive or crank it and see what happens......gimme twenty minutes!

[Z06scentair]

Ok I stuck the fuel pump assembly back in the car.

When I changed the plugs the number seven plug valley had fair amount oil inside the boot and the od of the plug.

I cleaned the valley out pretty well hoping the cam cover seal would seal back up. Then installed the plugs, I put di-electric grease in all plug wire ends.

Drove the car around and it ran great.

Fast forward to yesterday and the mis started. After putting the fuel pump assembly back in i decided to recheck the plug wire grease.

To my surprise all the grease had hardened or thickened up and was lacking.

Re-applied new grease to all the plug wires.....once I got to #7 I saw once again the oil had saturated the plug and wire boot. I cleaned the oil off again re-applied grease and once the car was started the mis was gone. Drove it up the road and it ran fine.

Guess I have found my culprit.

[Paul Workman]

Originally Posted by Z06scentair

car ran fine for 20 miles and was filled with fuel then straight home

Well, first step would be to isolate the cylinder(s) not firing.

That said, funny you should mention filling it with gas and then having a miss. I had that exact problem this past week. Truck ran fine, filled it with gas and let it sit over night. Next time out...missing like a muthah! Ran some liquid "Heat" into the tank and now it runs as if nothing happened, except for the SES light, and even that went out this morning.

We've gotta know which cylinder(s) are involved, methinks...