Why the miss ?

[roger longman]

Hi everyone, I'm hoping someone can point me in the right direction. If my vette is in overdrive below 53 mph and pulling it misses a beat. plugs, wires, cap, etc. I changed. The engine just doesn't like pulling at low rpm. A vette specialist told me that OD. was just to high a ratio and I should wait until I was doing over 55 mph before before selecting it. Having serviced my car for the previous owner, he also said it was quicker than standard but could not say what had been done to it. I wonder whether the cam had been changed or something else done to make it a little less "forgiving". Could someone please give me ideas ? roger.

 

[vetteboy86]

I've never had any issues when my car shifts into OD at speeds lower than 55. As a matter of fact I have conducted many tests lugging the car up inclines in overdrive and checking for spark knock.

Is it occasional or does the car shudder?

 

[roger longman]

Hi vetteboy86, thanks. It's occasional, seems like every 100 revs or so. Is spark knock pre-ignition ? If so it isn't that. Roger.

 

[vetteboy86]

I'm having a hard time imagining what is actually going on. Take a look at the attached file. A pretty good read.

So is the car jerky? You can actually feel it chugging?

 

[roger longman]

Hi vetteboy, No it's neither pre-ignition nor detonation. It's not missing as in "running on 7" it's as if it were sometimes missing a beat, such as if a plug was partially breaking down under load at low rpm but I've just replaced them with wires trying to resolve the problem. It's not jerky nor chugging. Roger.

 

[roger longman]

Now it's getting worse. If I start off in OD it changes gear at lower rpm and when reaching 35 mph Starts chugging badly and I have to change down also it is getting about 3 mpg less in town. Please help. Roger.

 

[Vettefan87]

What brand of plugs, wires, and cap did you put on? Did you change the coil and the rotor as well?

 

[vetteboy86]

Confirm the work you have done, starting with plug wire routing. I have done it at least twice. Mis routed a wire, when I new I had it correct.

Is the SES light on? You didn't mention it so I suppose not. What does the car do idling? At similar RPM's in other gears does the condition exist as well?

 

[Schrade]

Hi everyone, I'm hoping someone can point me in the right direction. If my vette is in overdrive below 53 mph and pulling it misses a beat. plugs, wires, cap, etc. I changed. The engine just doesn't like pulling at low rpm. A vette specialist told me that OD. was just to high a ratio and I should wait until I was doing over 55 mph before before selecting it. Having serviced my car for the previous owner, he also said it was quicker than standard but could not say what had been done to it. I wonder whether the cam had been changed or something else done to make it a little less "forgiving". Could someone please give me ideas ? roger.

Can you post the name of the 'vette specialist', and business #? TPI DOES like low rpm's, so this 'specialist' ISN'T... Never mind any of his 'words'. Words go away when the sound stops. Get him to show you stuff.

Someone finally asked about codes (8 posts - ;squint: ). I'm bettin' you have one.

If not, do the basics - air, fuel, fire.
Air filter clear?
Fuel - static and dynamic pressure ok? (you NEED TO know - search my posts for FP tests).
Fire. Plugs and wires okay? Properly routed? Open the hood, running, PITCH dark, and look for the 4rth of July around the wires. Get a water spray bottle, and spray around the wires, and look for more discharge uh huh...

 

[roger longman]

Hi vetteboy,Vettefan and shrade, Thank you all for taking the time to help me. plugs FR5LS,wires Borg Warner 8mm, cap and rotor Accel. I didn't change the coil. The wires I replaced looked to be the originals ! One of which had been shorting. SES just flashes 12 and the fan comes on. Idles at 600 rpm when warned up. Only does it when OD selected but chugged badly at 35 mph, of course not fast enough to actually be in OD. Air filter clean,haven't checked fuel pressure, routed wires to avoid any contact and put additional insulation where they were close. Will run it tonight in the dark,just to be sure. Many thanks once again. Roger.

 

[vetteboy86]

As you might already know, 12 is the status LED, so it doesn't seem that there is a code set.

Do you suspect that perhaps the computer tune was edited at some point? So at 35, and shift selector in D you do not have this problem? What are the RPM's when this occurs in OD? It might be possible for the car to shift into OD at 35. At 40 mph in OD my RPM's are at 1k. No chugging, just normal driving.

 

[Schrade]

SES just flashes 12 and the fan comes on.

Fan coming on is a diagnostic clue. Can't remember if it's L98 or LT1, but you DO have an electrical problem. Seen it in FSM...

Cleaned my air filter once, and forgot the air mass sensor connector. Fired right up, stumbled, and started the fan (as it should have).

Knew right away too...

 

[vetteboy86]

With the key to run, and a jumper between terminals a and b on the diagnostic connector, the fan will run while retrieving codes. This is a normal function, at least in all my experiences it is. I can dig my FSM out tomorrow after work.

I have incorrectly programmed a tune, or accidentally put the IC in backwards on my moates adapter, and as soon as I keyed the ignition the fan ran.

 

[toptechx6]

Check fuel injector resistance with an ohmmeter both cold and hot.

 

[roger longman]

Hi everyone and thanks, Ran it in the dark, no arcing to be seen. I think it could well be shifting into OD at 35 mph when selected but in any event it would not run at 40 mph in OD unless on a decline. I will check rpm when I next take it out and report back. Problem with ohmmeter is, that as an electrician, I make a good road sweeper, but thanks toptechx6 I'll get it some how. I don't think the computer was edited but I don't know. The vette guy did say it was faster than standard ( Schrade, it's "THE FIBERGLASS BODY" in Inglewood California ). It's certainly fast enough for me. Roger.

 

[toptechx6]

Hi everyone and thanks, Ran it in the dark, no arcing to be seen. I think it could well be shifting into OD at 35 mph when selected but in any event it would not run at 40 mph in OD unless on a decline. I will check rpm when I next take it out and report back. Problem with ohmmeter is, that as an electrician, I make a good road sweeper, but thanks toptechx6 I'll get it some how. I don't think the computer was edited but I don't know. The vette guy did say it was faster than standard ( Schrade, it's "THE FIBERGLASS BODY" in Inglewood California ). It's certainly fast enough for me. Roger.

Check this link to some good information and a "how to" video on another forum, look at #5 to understand the testing procedure using an ohmmeter.

injector videos and questions - Corvette Forum

 

[roger longman]

Hi toptechx6, thanks a lot very informative. Roger.

 

[roger longman]

Hi everyone, O.K. here goes. I ohmed the injectors, all read exactly 18. I put the meter back into the box. THEN I SAW IT (hangs head ) sitting there in its blue and red box was the spark plug I hadn't replaced. That couldn't be the problem the other 7 were in very good condition. Remembering that no. 4 cylinder had been beyond the capabilities of my tools I had decided to do it at a later date with a different socket adaptation AND PROMPTLY FORGOTTEN THE FACT. Well I might as well do it now, so asked a mechanic friend if he had any suitable sockets, he came up with a "Snap ON" plug socket with a swivel base I had not seen nor heard about before. Out it came and ........ it was completely carbon fouled. New one in. Car is completely different, even exhaust note and resonance. I guess this was the plug that suffered from a bad wire and was breaking down. How can I be so stupid ? It gets easier the older I get. Thanks all, for the help and sujestions. Roger.

 

[LT4man]

Don't beat yourself up about this. We ALL make mistakes. I have almost forty (40) years in the auto & truck repair business. I still have a brain fart every now and then. Some of my friends (are you listening junk?) maintain it is more NOW than THEN!

At least the fix was easy and relatively painless! How about those swivel spark plug sockets? Cool, huh? I have several. And sometimes I still need to use my fingers!

AFTER REPLACING YOUR SPARK PLUG, PLEASE SAVE THE !

 

[Vettefan87]

...4 cylinder had been beyond the capabilities of my tools I had decided to do it at a later date with a different socket adaptation...

I think you can get that one out if you get a long extension and there is a little hole in the wheel well that you can slide it through. I know I have to get one plug out that way. Not sure if it is that one without looking.