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]

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]

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?


Were the injectors new or "rebuilt"?
Is it only one cylinder or two, and which one/ones?
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)
Did the car idle for a long time? (I.e., fouling the plugs)
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]

Some more info?


Were the injectors new or "rebuilt"?

new
Is it only one cylinder or two, and which one/ones?

not sure

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?

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]

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...

[Z06scentair]

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...

Yeah i agree filled with fuel and then. The tank was about empty maybe I stirred some setiment up?

Man not sure how to find the dead/weak cylinder?

[Paul Workman]

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]

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.

[XfireZ51]

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.

Sounds like you'll be pulling a cam cover.

[Z06scentair]

Sounds like you'll be pulling a cam cover.

:-({|=

How bad of a job is the drivers side? Do you really have to remove the brake booster?

Will i be able to lay the ac compressor over and not have to bust those lines loose?

[GSJoe]

I'm not sure what to tell you about the effect of the oil leak in the sparkplug well (oil, after all, is not a conductor), but I can tell you I've had a similar miss experience after changing plugs. After a bit of--hell, a lot of--chasing, it was suggested to me that the problem might be spark tracking on the outside of the plug thanks to ionized air in the boot. Removing the spark plugs once again, I found several of them had very fine track marks outside on the insulator. (I had to look hard to see them.) After replacing the plugs a second time and actually filling the sparkplug wire boots with dielectric grease, the miss was gone, and it never came back. I must emphasize that you have to fill those boots with dielectric grease! Hope this helps.

[Z06scentair]

Thats great news.....I too filled mine this time with grease. Where are you located in Charlotte?

Always glad to see someone close to me with one of these cars.

[GSJoe]

Glad you asked. I live in Highland Creek--north end of town, so to speak. I've had two of these great cars. The first was a 1990 which I bought new in 1990. The second 1990 I bought near here in 2011 with 53K miles on the clock. A friend of mine here in Charlotte bought a '91 a few years ago too but has just sold it. For a long time he and that car resided at my house. Our cars were similar, but there are some differences too. SIR issues, for example, seem to be more prevalent in the MY 1990 than in MY 1991.

[Z06scentair]

Glad you asked. I live in Highland Creek--north end of town, so to speak. I've had two of these great cars. The first was a 1990 which I bought new in 1990. The second 1990 I bought near here in 2011 with 53K miles on the clock. A friend of mine here in Charlotte bought a '91 a few years ago too but has just sold it. For a long time he and that car resided at my house. Our cars were similar, but there are some differences too. SIR issues, for example, seem to be more prevalent in the MY 1990 than in MY 1991.

My boss lives in highland creek right in front of one of the golf holes. Just tackled the SIR issue.

Im in Belmont NC and my car is a 1990 Red on Red.

I will pm you my phone number.

[rhipsher]

Paul the injectors are brand new FIC's from the same guy most of us get them from here.
If needing dielectric grease for the plug wires was true then mine should be missing like a mofo. Mine have been bone dry for 7 years and doesn't miss at all and I know that my plug wires are at least 12 years old.
Have you re torqued the cam cover bolts? Sometimes they will back out over the years an that's all it takes for the spark plug ring seal to allow oil to get in. Either way you have got to fix that. You will have to pull the brake booster. Oh and did I mention it's a bitch to pull. And it's even worse if your a fat guy:p And after you take care of that and still have a miss I'd look at the coils.

[Dynomite]

You will have to pull the brake booster.

Actually I was able to remove cam covers without removing Brake Booster ;)

Removing Cam Cover and Camshaft Timing Inspection (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-4.html#post1581665190)

[rhipsher]

Actually I was able to remove cam covers without removing Brake Booster ;)

Removing Cam Cover and Camshaft Timing Inspection (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-4.html#post1581665190)That will work as long as the cam bolts come out easily. But it they don't and you have to use an impact driver you will need all of the room you can get. Sometimes there's just no way around it. When I removed my can covers almost half of them would not come out without the torx stripping right out of the head. Using the impact driver was the only way I was able to get those out. Its an awesome tool.

[Z06scentair]

Just went out and checked the bolt torque and they all seem good an snug!

It efforts to not strip the heads off the bolts I will remove the brake booster for easier access.......ordered the o-rings from jerry today. Anything else I will need or should replace during this venture?

[XfireZ51]

Just went out and checked the bolt torque and they all seem good an snug!

It efforts to not strip the heads off the bolts I will remove the brake booster for easier access.......ordered the o-rings from jerry today. Anything else I will need or should replace during this venture?

You'll need the sealer for the cam cover. There is no gasket.

[rhipsher]

Once you get the cam covers off I'd replace that filter material that is stuffed into where the breather tube comes in. You'll find that the 24 year old stuff will crumble like the 10 commandments as soon as you touch it. I just used stainless steel brillo pad and stuffed it in there. But if you want the original stuff Jerry might sell it. The brillo works fine and will last forever.

[rhipsher]

You'll need the sealer for the cam cover. There is no gasket. Loctite 518 anerobic sealer is the stuff you will need.

[Z06scentair]

Cool fellows.....as soon as my brother gets caught up at the shop we will tackle this joker!