rednari2

iTrader: (1)

I have a miss while cold. It runs great when warm. It usually takes two minutes or so before running smooth. There are no codes and I sprayed the intake manifold at start up to check for vacuum leaks. I am leaning toward a dirty AIC and not defective since there are no codes. Any thoughts??

Che70velle

iTrader: (6)

AFR’s ok for first couple minutes?

rednari2

iTrader: (1)

Don't know about AFRs, meaning I do not know if the motor is running too rich or lean. My scanner only does codes and I do not have HP tuners,so I have no way to check the trims. But, spraying the manifold tells me it is not sucking air and so it is not lean.

I saw an interesting vid on you tube.The guy was having the same problem. It turned out to be a dirty AIC.

chevymec

iTrader: (19)

Leaking injector possibly. You could always pull the rails/injectors up and place a paper towel under them. If they drip any fuel with the key on or off, you know they are leaking. Or very possible it is the intake gasket even though carb cleaner doesn't make a difference or set any codes.

rednari2

iTrader: (1)

Nice tip about the injectors. I suppose the manifold could suck air from underneath where the spray wouldn't go.I am going to clean the AIC first and then go from there. Thanks to both of you for the input.

gagliano7

Take a temp gun and check all the exhaust primaries and if one is a lot lower that is the cylinder with the miss. I had a coil that would miss when cold at idle and at part throttle but was fine wot.

rednari2

iTrader: (1)

Thats a good point. I suspected a coil earlier but moved on from there after I checked the spark while running. This was on # 1, and it was good but the motor was hot. Besides, I was thinking about a temp reader. So, going to Harbor Freight this week is in the cards.

RB04Av

A few drops of water on each header tube after about 10 seconds of running was what we used back in the Ice Age.

rednari2

iTrader: (1)

Yea! I usually start a cold motor and touch each pipe with the back of my finger. :-)

RB04Av

That would probably work fine if your nerve endings are properly calibrated but is a little too up close and personal for me.

Che70velle

iTrader: (6)

I use a thermal laser point gun, as you guys are talking about, on the headers up by the flange to help tune with. Lots of other uses on/under the car as well.

rednari2

iTrader: (1)

I tried my tongue once....

CattleAc

iTrader: (7)

Was it cold out...did it stick like it does to the flag pole in the school yard...???

00pooterSS

iTrader: (40)

Inspect the plugs for excessive gap too. I've had that problem a few times with worn plugs. Fuel lights off much easier once the engine warms up. Could also be lean.

As chevymec said, could be intake gaskets leaking too. Had many that leaked that didn't respond to spraying with brake clean.

CattleAc

iTrader: (7)

To bad you don't have a way to scan it...I've had a bunch come through the shop that didn't change the idle with a shot of carb clean...but, with monitoring the O2 sensor voltage, would drive them pig rich after the shot without changing the idle...

00pooterSS

iTrader: (40)

Agree, after seeing it hardly ever work after 20 years of being a tech I've pretty much given up on spraying to find vacuum leaks. It works for me about 1 out of 20+ times or maybe even less.

I use a stethoscope to find vacuum leaks. I pulled the end off and attached a length of vacuum line to the end of the rubber hose with a vac line coupler. Then I stuck a piece of brake line up in the vacuum hose so I could also run the tip across exhaust looking for leaks, it works really well on vacuum leaks, exh leaks, I even use it for evap leaks sometimes.

Che70velle

iTrader: (6)

Brilliant!

LilJayV10

iTrader: (39)

Trying to find a vacuum leak with something with 02 sensors is pointless unless you are watching the 02 voltage and STFT. The PCM will immediately pull fuel out and you will not get the increase in RPM's like you will trying to find a leak with a carb engine.

You can also use a water bottle, drill an 1/8 hole in the cap, point and shoot. If you do have a leak, it will suck with water in and no you won't hydrolock your engine.

00pooterSS

iTrader: (40)

That works too. I start by watching STFT and LTFT, if I see overly positive number I know I likely have a leak.





Che70velle, this thing is wonderful for pin pointing, and I mean pin size hole pin pointing, leaks. Here's a pic of how I arranged it. I recently found a intermittently leaking bypass actuator on a whipple blower with this after the truck went to a couple shops and they couldn't find it. Some people like smoke machines but if it's a small leak it won't smoke enough to see the leak, but you'll hear it like a heavy wind noise through the stethoscope.

Che70velle

iTrader: (6)

I’m gonna build one of those. I like the hard line at the end for heat, but better yet accuracy. Sometimes plastic will rub and it makes its own noises. The metal line wouldn’t do that...I wouldn’t think.