Need Help With Engine Miss

[Zo6 LVR]

1995 LT1 55,000 miles. Up until a couple of weeks ago I have never had a problem with my engine. I changed the plugs with the OEM Delco plugs. No problem for a while but just yesterday when headed for the Bloomington Gold show I noticed only when the A/C is on at idle in drive the engine misses frequently. A/C off or in neutral with the A/C on no miss. I realize that with the A/C on there is more load and apparently just enough to cause the miss. I have not changed the plug wires or cap & rotor or the opti unit. If it is a bad plug or wire, what is the best way to isolate the culprit? Or any other thoughts anyone may have as to the cause of the miss or related cures.
Thanks

 

[Itshakes]

Engine Miss

Tighten your intake manifold bolts. It sounds like a vacuum leak. Look for loose/broken vacuum hoses too.

 

[Zo6 LVR]

Thanks, I'll check that.

 

[John Robinson]

I noticed only when the A/C is on at idle in drive the engine misses frequently. A/C off or in neutral with the A/C on no miss.

Under the right side fuel rail cover is a vacuum check valve it has two vacuum hoses coming out of it one is for the cruise control and the other is for the temperature control unit in the car. Check to be sure that the plastic hoses have not become brittle and are leaking at the connection to this valve. You can check the valve by sucking on the vacuum side and putting your finger over one hole at a time on the two outlet holes. If you can pull air through either side the valve is bad. Be sure to get the OEM valve they are less than $10.

 

[Zo6 LVR]

John,
I had to replace that valve when I bought the car because it was brittle and broken, I checked it again and all is well there. What is the reason you are thinking vacuum rather than ignition? The A/C needing to be on to have the miss occur?

 

[John Robinson]

John,
I had to replace that valve when I bought the car because it was brittle and broken, I checked it again and all is well there. What is the reason you are thinking vacuum rather than ignition? The A/C needing to be on to have the miss occur?

It could be ignition but I usually start with the things l can do without spending a lot of money at first. With these cars it seems that most people jump right on the opti or ecm or whatever cost the most. It could be the opti has corrosion in it from not being driven and heated up to evaporate the moisture that naturally would creep into it in storage. It also could be corrosion in the electrical connector that goes to the opti. (this happened to me) My point being start small and work your way up the food ( money) chain. And don't forget all the ground wires that could also have corrosion giving you a week ground on part of the wireing circuit.
Or the wires that were chewed by a mouse while in storage.

 

[LT4man]

1995 LT1 55,000 miles. I changed the plugs with the OEM Delco plugs. No problem for a while but just yesterday when headed for the Bloomington Gold show I noticed only when the A/C is on at idle in drive the engine misses frequently.Thanks

After spending almost forty (40) years working on and diagnosing engine problems, I have learned a few things.

First one is: Go back to the scene of the crime. In other words check the work you have most recently done.

Make sure ALL of your newly installed spark plugs are snug and not loose. At the same time make sure that ALL of your ignition wires are securely attached to the spark plugs. If you need to crimp the end of an ignition wire a little to make it "click" onto to the plug, go for it!!! Each spark plug wire should attach with an audible "click"!

Then, report back to us!

AFTER CHECKING YOUR PLUGS & WIRES, BE SURE TO SAVE THE !

 

[John Robinson]

After spending almost forty (40) years working on and diagnosing engine problems, I have learned a few things.

First one is: Go back to the scene of the crime. In other words check the work you have most recently done.

Make sure ALL of your newly installed spark plugs are snug and not loose. At the same time make sure that ALL of your ignition wires are securely attached to the spark plugs. If you need to crimp the end of an ignition wire a little to make it "click" onto to the plug, go for it!!! Each spark plug wire should attach with an audible "click"!

Then, report back to us!

AFTER CHECKING YOUR PLUGS & WIRES, BE SURE TO SAVE THE !

Right on. When I did my plugs I thought I had the number 8 in tight but by rechecking all the plugs I found it was loose I also had a plug wire that had pulled down the wire far enough that the connector did not go over the plug. I also had spark jump because I had not correctly routed the wires back into the wireing looms.

 

[Schrade]

1995 LT1 55,000 miles. Up until a couple of weeks ago I have never had a problem with my engine. I changed the plugs with the OEM Delco plugs. No problem for a while but just yesterday when headed for the Bloomington Gold show I noticed only when the A/C is on at idle in drive the engine misses frequently. A/C off or in neutral with the A/C on no miss. I realize that with the A/C on there is more load and apparently just enough to cause the miss. I have not changed the plug wires or cap & rotor or the opti unit. If it is a bad plug or wire, what is the best way to isolate the culprit? Or any other thoughts anyone may have as to the cause of the miss or related cures.
Thanks

A/C demand sends a signal to the PCM to increase rpm's for the increased engine load. Even an intermittent signal shouldn't make it 'miss' (maybe lope, like a vacuum leak, maybe).

Misrouted wires will emit radiation, just like a nuclear bomb (so says the FSM, and so says me, after chasing down faulty codes for 10 weeks last summer, due to one slightly bad wire which you couldn't even tell at idle).

Look under the hood in COMPLETE darkness, idling, and watch for a 4rth of July show from misrouted wires.


edit:
copy on your last post..........