# 94 chevy 4x4 truck problem



## tecate1987

94 chevy truck 5 speed, vortec 4.3 v6 engine.

truck is running rich, has new air filter, plugs. 
What can be causing this ???


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## Gary_602z

Thermostat stuck open or a bad computer temp sensor could cause it to run rich.

Gary


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## tecate1987

*truck*

it happens pretty much from start up.
is the temp sensor the same part as this on ebay.? item #250355290617

temp control ?


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## Gary_602z

tecate1987 said:


> it happens pretty much from start up.
> is the temp sensor the same part as this on ebay.? item #250355290617
> 
> temp control ?


No that is an A/C temp control. 
I was talking about the Computer temp sensor that send the engine temp to the computer. There is also a sensor for your temp guage or light which would be different

Gary

Have you checked for any codes?


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## mspeckhem

another thing you might try to check is, pull the engine oil dipstick out and smell the oil on it, if it smells like gasoline, you could have a fuel injector or fuel injector line problem, those vortec engines have plastic lines inside the intake plenum that sometimes will crack, and make the engine run extremely rich, and dump fuel right down into the crankcase and evantually ruin the engine., i would also check for codes , it is very possible it could just be a coolant temp sensor, or even a different problem, i've seen bad vacuum lines to the map sensor also, although i cant think right off the top of my head if that particular one has a vacuum hose or if it is directly mounted into a vacuum port. 20 plus year ase master mechanic, just thought i'd throw some quick ideas at ya.


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## ratherbefishin'

Check the fuel pressure and pull codes. Could just be the fuel pressure regulator. If so, the only code it would throw would probably be one indicating the O2 sensor is detecting a rich condition.


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## tecate1987

*chevy*

I am going to see if my coder will read with this year truck.
If the weather clears up some today. I will also check the oil smell.
thanks for the help, I will reply with updates.


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## Rehabber

VERY high possibility of bad fuel pressure regulator. The diaphram pops and leaks fuel into the intake manifold. A pressure check may not determine this leakage.


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## 47_47

A fuel pressure regulator will fail in one of two ways. Either cause high fuel pressure (measure with a gauge) or bypass internally as Rehabber stated. To check for a bypass, remove the vacuum line from the regulator and check for fuel.

I'm leaning toward a bad ECT or thermostat.


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## newbsauce

Is it showing a code? Please pull the code (or go to advanced auto/autozone) to have them pull it.

Alot of people jumping to some serious conclusions on this thread. My thoughts (in this order):

1> O2 sensor
2> FPR
3> Temp sensor
4> Dinosaur attack caused fuel problem


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## 47_47

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.

http://www.troublecodes.net/GM/

Engine control diagnosis starts with retrieving codes, undertanding what it takes to set the fault, following trouble trees and knowing what normal readings are. It does NOT mean read a code and hang a part. 

I'd start by getting a scanner, measure and compare the ECT readings. If you watch the scanner, you will also know when the tstat opens at around 190°. Good luck.


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## newbsauce

47_47 said:


> 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 time, then proceed to the next code.
> 
> http://www.troublecodes.net/GM/
> 
> Engine control diagnosis starts with retrieving codes, undertanding what it takes to set the fault, following trouble trees and knowing what normal readings are. It does NOT mean read a code and hang a part.
> 
> I'd start by getting a scanner, measure and compare the ECT readings. If you watch the scanner, you will also know when the tstat opens at around 190°. Good luck.


Good information. Not sure about the setup of your car, but rather then using the scanner, I simply grab my upper radiator hose. There is a huge temperature difference when the Tstat opens  Granted, I know my cars normal operating temp, and trust my gauge.


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## Clutchcargo

How do you know it's running rich?
Is the check engine light on? 
Pull the codes for a start.
My guess would be the O2 sensor.


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## 47_47

newbsauce said:


> Good information. Not sure about the setup of your car, but rather then using the scanner, I simply grab my upper radiator hose. There is a huge temperature difference when the Tstat opens  Granted, I know my cars normal operating temp, and trust my gauge.


Yes this would tell if the tstat is opening, but will not give any information about the coolant temp the computer senses vs the actual engine temp. BTW this truck should have 2 coolant sensors, one for the gauge and the other for the ECM. 

To the OP, with a scanner look at the integrator. Ideally it is at 128. With a rich running engine, the integrator will go down. Usually down around 100 I start looking for rich conditions.


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## tecate1987

*truck running rich*

ok, I havent checked must due to cold and wet weather.
But,

there is not check engine light on, it does work cuz it lights before starting engine. It has obd, and my scanner is obdII, I cant plug that in.
Also, truck is plow truck and not street legal to take to autozone. 
Oil smells fine. going to try to check thermostat for sticking, and also pull vacuum line off fpr to check for extra fuel.
thanks for all the help so far, if I run into more info I will provide and any other ideas are appreciated, thanks.


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## 47_47

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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## SELLC

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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## tecate1987

*chevy*

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 ?




> 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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## SELLC

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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## mspeckhem

have also seen bad gasket at intake plenum causing low vacuum to MAP sensor, making the engine run rich


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## tecate1987

*pins*

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



> 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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## 47_47

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

http://www.troublecodes.net/GM/


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## tecate1987

*thanks*

I clicked it after I posted last post, I thought it was only codes, not a diagram.


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## tecate1987

*4.3 engine*

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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## SELLC

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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## tecate1987

*chevy*

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.


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## SELLC

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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## SELLC

I almost forgot to ask,

How is the cap and rotor? How about the wires?


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## 47_47

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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## tecate1987

*truck*

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.


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## 47_47

tecate1987 said:


> 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 bearly idle.
> smoking with gassy smell. no check engine light ever came on. It will light when first starting the engine, but dont stay on.
> 
> 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.


Does this have TBI (throttle body injection, looks like a carb) or ported injection? How many miles?

Start with the basics check the cap and rotor for carbon tracking.

Check the PCV and EGR valves. Both are calibrated vacuum leaks and will give a lean misfire. 

With the air cleaner installed spray carb cleaner around the intake and vacuum line. If it changes you have a vacuum leak.

If you have a good pair of insulated spark plug wire pliers you can carefully remove one plug wire at a time at the plug and note idle. If it changes, that cylinder is working. Be careful, secondary ignition voltages are high.

High mileage check timing chain. Remove distributor cap and by hand rotate the crankshaft pulley in opposite normal rotation, until the rotor moves. Rotate crank by hand in direction of rotation and note the number of degrees the crank moves until the rotor moves. It should not be more than approx 10°.


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## SELLC

tecate1987 said:


> the truck has the central intake system,
> 
> for firing order which is #1 plug on the cylinder fire wall or rad driver side.


#1 would be on the forward most mounted head twards the radiator.

CFI or "Central Fuel Injections" is another term for TBI or "Throttle Body Injection". One and the same. You do not have a mass air meter.

Bosch Platinum are not the best for your model, but they will work. Best to have Delco plugs in there.

If the vehicle sits most of the time, you should be starting it once a week and letting it get up to temp. A vehicle that sits for long periods of time without being driven is not good. The rot seems to set in.

Sounds like you are getting a code 12, which just means you are in diagnostic mode. Best to check that ignition system real good.


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## tecate1987

*truck*

I did find the numbers for the firing order on the intake. It is also correct firing order.
I took off the dist cap, didnt look real good. corrosion, little ball in the middle was about gone, replaced cap and rotor. Still no better.
It wont even move, it does seem to get worse when it gets warmer.
I sprayed carb cleaner around the vacuum lines the other day, no change in idle. I tried running truck in the dark to see if any sparks in wires or anywhere. Nothing.

Truck does have 186,000 miles on it, ran good all last winter, and few times this summer. Yes, throttle body injection. I will try pulling plugs when running, and


> Rotate crank by hand in direction of rotation and note the number of degrees the crank moves until the rotor moves. It should not be more than approx 10°.


 but I wont be able to get to it til friday.
Thanks for all the help so far, very informative.
where is the egr valve on this truck ?


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## 47_47

Also remove the wires from the distributor cap (one at a time) and check for corrosion.


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## tecate1987

*truck issue*

got to work on the truck a little today. 

It runs, when I took plug wires off, the right side 6, 4, 2 wires, one at a time it changed engine very little when I disconnected a single wire.
Even put #6 and 4 wires in each others location, really didnt change the idle as much as it should.
The left side, it made the engine either stall or chug really bad like it should.

Sprayed carb cleaner around vacuum lines, no change in idle.


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## 47_47

I'd do a compression test next. Not familar with the exhaust system, but does your truck have one convertor and one muffler or do you have one for each bank?


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## tecate1987

*truck*

it has single exhaust, single muffler and convertor.
all comes from engine thru Y pipe.


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## tecate1987

*truck*

I did a compression test, all cylinders were approx 150-153.
cyl number 2 was 146.

got a different coil to try, hopefully today.
any other ideas ?

coil didnt make any difference


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## tecate1987

*truck*

here is some pics of the engine.
I have read some other site and all keeps pointing to gas lines under the plenum, does this type of injection system have this and to I have to take the whole intake off or just the throttle body ?


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## BigWalt

Here's what you should do....[one step at a time]
1... turn the key on with engine off. Look at fuel injectors .....they should not be dripping with fuel....if they are, then no amount of cleaning will fix it....replace it...

2...You got throttle body injection system, the fuel pressure regulator diaphragm are known to leak and dumped fuel badly.

3.... remove oxygen sensor(s) from your exhaust pipe. Start engine, observed your engine running condition, if it smooth out, then your cat converter is clogged!


FYI... I know I'm newbie here, I'm ASE certified Technician, Senior Ford Master Tech and GM Tech....no bull manure about it...


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## tecate1987

*truck*

I checked the injectors, there is no leaking or drips from them.
Does this have the spider injection system in it ?


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## BigWalt

tecate1987 said:


> I checked the injectors, there is no leaking or drips from them.
> Does this have the spider injection system in it ?


 
Did you make sure the key is on fully?

No you do not have spider injector system......

do you have fuel pressure guage?
If not, rent one or buy one.
If you don't know how to use it then get mechanic friend to show you, it must be handle with care otherwise you got fire hazards.

Hook up fuel pressure guage and observe fuel pressure with* key on, engine not running.*
Fuel pressure system should hold pressure, if not then you got rupture fuel pressure regulator.

One more thing.....you asked me about spider injector system......you shouldn't be asking me that question if you did actually look at fuel injectors.
You have 2 fuel injectors, see if you can use MS paint shop and circle the injectors and then post it back here....I want to make sure you know where to look for.


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## 47_47

In the second photo, are the injector wires insulation nicked?


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## tecate1987

> One more thing.....you asked me about spider injector system......you shouldn't be asking me that question if you did actually look at fuel injectors.
> You have 2 fuel injectors, see if you can use MS paint shop and circle the injectors and then post it back here....I want to make sure you know where to look for


I did look at the injectors, but everything I found online about the 4.3 says spider injection unit, so I didnt know if I had the injectors, that went into a spider unit below the throttle body. I knew it didnt have the normal plenum style.
Anyways, thanks for the info. I will check fuel pressure.


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## tecate1987

*still need help*

truck still not running, wont hold idle, barely runs.
still running very rich, passinger side dont appear to be firing.
new 02 sensor, cat removed. 
checking pressure today.


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## tecate1987

*truck*

fuel pressure is about 12 lbs. seems to hold at this pressure also.

a wire does have a small nick in it onthe injectors. but its on the side that seems to be firing ok.


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