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Old 10-09-2009, 03:14 PM   #16
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94 chevy 4x4 truck problem


Has this truck see any run time recently? If you are not running it long enough, you will not get into closed loop operation and it will run rich.

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Old 10-11-2009, 04:18 PM   #17
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94 chevy 4x4 truck problem


Possible MAP sensor or vacuume line is broken.

Usually the check engine light will go off if any of the sensors are out of range.

You could also have a problem with the Mass Airflow sensor. Tap on it while its running to see if the idle changes.

How is the idle? Smooth or choppy? Are the converters removed? If so this could be the problem, as the converters burn off the unburnt gas.
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Old 10-11-2009, 07:27 PM   #18
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94 chevy 4x4 truck problem


I changed the thermostat, old one was rusty, but didnt appear stuck.
I dont see any gas in the vacuum lines. There is no check engine light on. It wont seem to hold idle, runs choppy, and has unburnt gas smell in smoke its letting out. Dont have smell of bad eggs like convertor is plugged. Is this still possible? All vacuum lines seem good.
Is there a way to check map sensor? or mass air flow sensor ?


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Possible MAP sensor or vacuume line is broken.

Usually the check engine light will go off if any of the sensors are out of range.

You could also have a problem with the Mass Airflow sensor. Tap on it while its running to see if the idle changes.

How is the idle? Smooth or choppy? Are the converters removed? If so this could be the problem, as the converters burn off the unburnt gas.
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Old 10-11-2009, 09:52 PM   #19
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94 chevy 4x4 truck problem


Usually the thermostat will have very little to do with how the vehicle runs, unless its over-heating or you dont have heat inside the cabin.

Another thing that can cause the vehicle to dump too much gas is a coolant temp sensor. If this is out of range it will make the vehicle run rich or lean.

The Mass Airflow sensor will usually set off the check engine light, however it is located up stream of the throttle body, usually between the rubber snorkles. While the vehicle is running tap on it (Not too hard) and see if it effects the idle. Sometimes the filaments can be loose.

The MAP sensor has one vacuum line going to it, with a three wire plug. Some of them mount directly to the manifold to get vacuum. Usually this will set a code also, however if the fault is in the vacuum side, it wont.

Also be sure that all the plugs are gapped proper, and the fireing order is correct.

You wouldnt happen to have a photo of the engine would you? I might be able to point it out.
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Old 10-13-2009, 11:57 AM   #20
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94 chevy 4x4 truck problem


have also seen bad gasket at intake plenum causing low vacuum to MAP sensor, making the engine run rich
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Old 10-13-2009, 02:56 PM   #21
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94 chevy 4x4 truck problem


47_47
what pins are A & B?
it has the D shaped plug.

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This truck has OBD. I think Autozone can read only OBDII codes. The OP did not state if the SES light is on, usually that is the first complaint stated. To read the codes on this truck, turn the key on and jumper pins A & B of the ALDL. You will count the flashes of the SES light. You always will read one flash, a brief pause then two more flashes (code 12, no RPM and is normal). The MIL will flash this code a total of three times, then proceed to the next code.
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Old 10-13-2009, 03:09 PM   #22
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94 chevy 4x4 truck problem


Instead of trying to explain, this link will show the pins to jumper.

http://www.troublecodes.net/GM/
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Old 10-13-2009, 04:02 PM   #23
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94 chevy 4x4 truck problem


I clicked it after I posted last post, I thought it was only codes, not a diagram.
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Old 10-13-2009, 05:20 PM   #24
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94 chevy 4x4 truck problem


whats the plug gap suppose to be on this engine., and firing order to recheck it ?

also I changed the temp control sensor, it was only $13. so worth a try.
still didnt fix problem.

truck sputters on acceleration, really dies out when trying to drive, chuggs when in N, and begins to pick up rpm's seems to clear up some, but not all the way.
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Old 10-13-2009, 07:02 PM   #25
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94 chevy 4x4 truck problem


Usually AutoZone will perform a scan test at no charge.

Spark plug gap should be at .035

You can also test the TPS (Throttle Position Sensor), however the problem sounds a lot like a MAP or MASS AIR problem.

Are you able to get a photo of the engine? I can put little pointers to all the sensors so you know what ones to start tapping and testing.

Are you SURE the firing order is right? Having two switched will yeild the same kind of complaints you are talking about, was it was doing that before you did the tune up?

Are you letting the vehicle warm up to 190 degree's?
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Old 10-13-2009, 07:13 PM   #26
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94 chevy 4x4 truck problem


I will try to take pic wednesday. What is the firing order. I have the plugs gapped at .045. I read some other sites posts saying .045. It dont show on the schroud, tag is gone.

I havent let it get to 190degrees, it basically wants to stall too much.

Last edited by tecate1987; 10-13-2009 at 07:32 PM.
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Old 10-13-2009, 07:31 PM   #27
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94 chevy 4x4 truck problem


I checked on the AutoZone web-site and it claims it is .045

This will make a little hotter spark. I usually gap any copper plugs at .035 on the Chevy engines as they burn down so fast. If your using a platinum plug then keep it at .045

Most all 350's are at .035 and the 4.3 is really a 350 with two cylinders shaved off.

Being a 1994 its right on the edge. Your truck could be a port fuel injected engine, and it could also be the older central fuel injection. The PFI models will have an injector at each cylinder, while the CFI will have one centeral injector in the center of the intake. The CFI unit will almost look like a carb. Also important to note is the CFI engines do not have a mass air sensor, so they rely heavy on the MAP (Manifold Absolute Pressure Sensor) to control fuel.

Here is a photo of what the MAP sensor looks like


Here is a photo of what the air charge sensor looks like (This is NOT the mass air sensor)



I would really need a photo of the engine to figure out what injection system your truck is running, and if it has a Mass Air Sensor.
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Old 10-13-2009, 09:23 PM   #28
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94 chevy 4x4 truck problem


I almost forgot to ask,

How is the cap and rotor? How about the wires?
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Old 10-14-2009, 06:49 AM   #29
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94 chevy 4x4 truck problem


Should be 1-6-5-4-3-2, check on the intake.

Added: There have been too many guesses so far. What exactly does the truck do, when did the problem start (did you do something prior), what testing have you done and what parts have you changed?
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Last edited by 47_47; 10-14-2009 at 07:00 AM. Reason: Added
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Old 10-14-2009, 02:23 PM   #30
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94 chevy 4x4 truck problem


the truck has the central intake system,

started couple weeks ago, its not used much, just for plowing. I had it running in the summer just to move it etc.
truck is running rich, sputtering when acceleration in neutral, will barely idle.
smoking with gassy smell. no check engine light ever came on. It will light when first starting the engine, but dont stay on.
got no errors when searching for codes, just 1 then 2 flash.

plugs are bosch gapped at .045
has new air filter, temp control sensor, and thermostat. wires are only 1 year old,
going to check cap and rotor and timing today.

I did put some gel for batteries on the plug ends so they wont stick, but I cant imagine this would hurt, its mostly on the rubber boot.

for firing order which is #1 plug on the cylinder fire wall or rad driver side.


Last edited by tecate1987; 10-14-2009 at 03:06 PM.
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