Carguy00

I have a 97 Malibu 3.1 that has an intermittant starting problem. It does it when hot or cold. It happens about 3 times a month. Have tried a few things.

Fuel pressure regulator.
Idle-air control x3.
Reprogrammed computer.
Fuel injector flush.

When it is not staring I can take out the IAC and spray carb cleaner into the port, reinstall the IAC and it will start.
I can take off the intake hose and spray cleaner into the TB and it will stay running until I quit spraying. BTW I can always hear the fuel pump running.
When it first started doing this I would tap firmly on the IAC and it would start? Who knows why, I can't figure this thing out. NO codes in the computer either.

Any help is greatly appreciated. You guys have helped me out before with my TA hopefully we can do business again.

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86 Trans Am
red/silver t-top
305 TPI

ede

do you have good fuel preasure? no codes would seem that your iac and other eletronic controls are working correctly. air cleaner, fuel filter, a good tune up.

Carguy00

The fuel pressure has been checked twice and it's ok. I have never checked it when it is acting up though.
Has new fuel and air filter.
Also has new plugs and wires.

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86 Trans Am
red/silver t-top
305 TPI

sparky

have ever checked for injecter pulse when it doesnt start?
could be problem with crank or cam sensor

86Z

iTrader: (4)

that's what i was thinking, most likely it's the crank sensor.

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86 Camaro with 88 305 LB9 converted to carb, edelbrock performer manifold, S/R Torquer Heads, Hedman Headers, Crane Compucam 2032 edelbrock cat-back, gutted cat, slp underdrive pulley, mallory ignition, 305 h.o dual snorkel air cleaner, hypertech thermomaster chip,160 degree thermo, and fan switch, 5-speed, 3.23 posi

95 Beretta Z26, 3100 V6, 4 Speed auto, stock

zippy

haven't seen that problem yet, but i can check it at work. need to check fuel pressure though when the problem occurs and check for injector pulse when it's happening. also check for spark when it happens.

Carguy00

I have checked for spark when it is happening and that is not the problem. How do I check for fuel injector pulse?

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86 Trans Am
red/silver t-top
305 TPI

sparky

unplug an injecter and plug a noid light in
basicly its an led
then start and watch for the light

zippy

if you are showing spark when it happens, you not likely to have a crank sensor problem.

Carguy00

Do you guys think it coould be the contol module? The car wouldn,t start abain this morning and I had to take off the IAC and spray into the port to get it started again. Why would the extra fuel make it start and keep running? It sounds like it wants to start, but just wont.

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86 Trans Am
red/silver t-top
305 TPI

Vader

CG,

You've got spark. You've got compression. Your fuel pump is apparently running. You obviously aren't getting fuel when this occurs, or the spray cleaner wouldn't do anything but clean.

Tapping on the IAC is actually indirectly tapping on the throttle body. If this has helped the condition, you might want to take a look at the TPS connector, and TPS itself. If you have a "dead" spot in the TPS, you might be getting no fuel injector pulses since the PCM has no reference voltage to learn as a "zero" throttle point. The next time it occurs, shut off the ignition and operate the throttle pedal from idle to WOT a few times to move the TPS wiper to a different position. You might even try cranking with a little extra throttle applied to get a TPS reading to the PCM.

One more thing about spray carburetor cleaners. They are a solvent designed to dissolve varnish, gum, and carbon. Remember the TPS? It has a metal wiper that rides on a carbon block to vary resistance in the circuit to the PCM. If you are over-zealous with the spray cleaner, the carbon in the TPS can be dissolved along with all the external contaminants. Just a hint.

By the way, even with a completely shut IAC, you should be able to compensate with the throttle to get enough air to start the engine.

The other main possibility is that the MAF is not sensing any air flow at cranking, so the fuel pulses may be too short or non-existent. Check the electrical connections at the MAF, and inspect the air intake ducts and hoses for leaks, splits, cracks, etc. I'm not sure about your PCM, but you might not get fuel without a MAF signal, just like the TPS.

A failed IAT or CTS sensor would likely be an open circuit, which would signal the PCM that the temperature was extremely low. This would tend to admit more fuel, not less. Shorted IAT/CTS wiring or sensors would indicate a hot engine, but still not completely cut fuel pulses. And the HO2S are basically ignored at immediate startup, and even a heater/sensor failure would not cut fuel. About all that's left is the crank trigger, and if you're getting spark, that is essentially ruled out.

Good luck.

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Later,
Vader
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[This message has been edited by Vader (edited September 20, 2000).]