SentimentalValue

A few months ago after doing a full tuneup on my car it ran perfect for about 24 hrs, then decided it would start missing on a couple of cylinders. I had the car diagnosed and then I replaced the spark plugs and wires on the two pistons that were not firing under a load. Now a month later after the car was running perfect, it is missing again on one cylinder this time.

So, how can you find out which piston is missing without getting charged for a diagnosis every time. Will TTS Datamaster, LT1 Edit, or Tuner cat do the job or is there an old-school method of doing this?



P.S. Last time when piston 2 and 5 were misfiring the mechanic said it was the plugs and not the wires. They were brand new AC Delco plugs and I am just wondering if the heat coming from the pacesetters that I just put in would cause the plugs to quit firing. Seems crazy to me, but just wondering. I am also going to order OTVC wires in the next 5 minutes...

Thanks.

fredmr39

not sure,

maybe you would notice a temp difference on headers (lower = missing?)

pull a plug wire - on the plug that's missing - it should sound "different" than the noise when you pull all the other plugs?

--I can't see any of this working unless it is a constant miss though...

brokegenetic

you might need to get insulators for your wires, the heat probably melted through the rubber somewhere on the plug wire causing to arc to the headers. only methods I know is to check the plugs to see which one is not firing.

crazydavez28

i'd imagine that an good old timing light would tell you if it's firing or not

Kevin Blown 95 TA

Well, the old Sunscopes were good for dropping a cylinder electronically, then you just watch the rpm's on a dwell meter and see if they drop or not. No drop, dead cyl. On your car you could pull a plug wire or remove an injector connector and watch the tach, but it's hard on a car that tries to adjust the IAC to regulate the idle - maybe you could disconnect that to disable it just for the test, i don't know. Like the other guy suggested, if you can borrow an infrared thermometer, maybe you can get a clue from looking at the headers. If you are OBD2, then you can get misfire info from a scanner. Check it at night and spray water on the suspect wire from a squirt bottle and see if there's some arcing. you could also swap injectors from side to side and see if the problem moves, if you suspect those.

EnerjetF67

A GM tech 2 will allow one to shut off each injector, which will allow one to spot a miss...that's what I use.
Any tool that will allow one to shut off fuel or spark to individual cylinders will allow one to spot the dead one.

SentimentalValue

What is the GM tech 2? That's not the ridiculously expensive machine they use to diagnose cars at the dealership is it?



I am not OBD2 so that option's out.

If I use a timing gun won't that just light up if the spark is going through the spark plug wire? So if the problem is the plugs I would never know the issue.

Also, I have the 1200 degree sleeves on all of my wires.

IllusionalTA

1200 deg radiant heat.. not 1200deg direct heat.. Check the wires.. the boot's are not going to burn.. but they will transmit the heat through to the wire.. don't ask me how i know...

cehan

Does it misfire at idle? Old school method is to get a probe (like an icepick) and attach a ground jumper. Then probe each spark plug boot with the engine running, and listen for the cylinder that doesn't cause the engine RPM to drop as much as the others. This is more effectively done with an automatic car, because you can have someone in the car put it in drive, bring the revs up while holding the footbrake. This puts the engine under load and makes the misfire more pronounced.

SentimentalValue

If it does misfire at idle, it's not as easy to feel it. Why is it that sometimes cars misfire under load vs. at idle, seems to me like if they would do it they would do it all the time.

EnerjetF67

A GM Tech 2 works with both OBD 1 and OBD 2 vehicles, and yes, it is the "ridiculously" expensive (Around $2,000.00) tool the dealers use.