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Amedee
Amedee, ASE Master Tech
Category: Car
Satisfied Customers: 21884
Experience:  ASE Master Tech advanced level specialist. Wisconsin certified emissions state inspector
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1993 isuzu: 4x4..with a 3.1 V6. it is back fireing and stalling..cap

Customer Question

i have an 1993 isuzu 4x4 pickup with a 3.1 V6. it is back fireing and stalling. i just changed the distributer cap ,rooter, wires and plugs. is therer anything els i can do to it before i put it in the shop. oh and would the map sensure have anything to do with it
Submitted: 3 years ago.
Category: Car
Expert:  Amedee replied 3 years ago.
Hello!

Are there any codes in the computer?

When does the engine back fire? At idle or under a load?
Customer: replied 3 years ago.
i didnt get the codes and it idles fine just back fires under a load
Expert:  Amedee replied 3 years ago.
Have you checked the fuel pressure when this happens?
Customer: replied 3 years ago.
how do you do that
Expert:  Amedee replied 3 years ago.
It sounds to me like you might just have a bad/weak fuel pump. Just hook up a fuel pressure gauge to the fuel rail and take a reading when this problem is happening. Check to be sure that the fuel pressure is within specs. Fuel injected cars are very fuel pressure sensitive. Fuel pressure is very important and must be within specifications! But if the pressure is low, it does not mean the pump is bad. A plugged fuel filter, a pinched line, and low voltage at the pump can contribute to low fuel pressure. All three must be check before replacing the pump! Fuel pressure testing is frequently overlooked but it is one of the common causes of poor performance and hard/no start conditions.

A good way to check your fuel pump is to run an amp test on the fuel pump while it is running or while battery voltage is being applied ot it (turning the key on, cranking your vehicle or even when your engine is running. The amount of amps your fuel pump will pull will depend on how much fuel pressure your fuel pump should supply to your fuel rail. A good rule of rule of thumb for this test is as follows:

14 to 15 psi 3 to 4 amps

30 to 45 psi 4 to 7 amps

45 to 50 psi 7 to 8 amps

50 to 70 psi 8 to 12 amps
Customer: replied 3 years ago.
i think its getting to uch fule
Expert:  Amedee replied 3 years ago.
How do you know?
Customer: replied 3 years ago.

it smells fluded

Expert:  Amedee replied 3 years ago.
I would check the fuel pressure regulator. It is located on the fuel rail. It is round, about a quarter size and has a vacuum line going to it. If the regulator is leaking gas than it can cause this problem. Pull off the vacuum line that goes to the regulator. Be absolutely sure there is no gas in the vacuum line. If there is, the diaphragm has ruptured and there is gas entering the engine that is not accounted for and the regulator will need to be replaced!
Customer: replied 3 years ago.
does it need to be running when i check it
Expert:  Amedee replied 3 years ago.
I would check it with the engine off.
Customer: replied 3 years ago.
there is nothing on the fule rail .the fule rail comes from the filter to the corb
Expert:  Amedee replied 3 years ago.
Do you have 6 individual injectors?
Customer: replied 3 years ago.
no i have a double barrel corb with two injectors its a gm 3.1 V6
Expert:  Amedee replied 3 years ago.
That would be correct. Sorry about the confusion.. i pulled up the wrong vehicle.

Lets pull codes from the computer. You can jumper terminal A and B on the diagnostic connector and turn the key on. The computer should flash the check engine light to display any codes in the computer.
Customer: replied 3 years ago.

the check engine light is going to flash to give th the code

Expert:  Amedee replied 3 years ago.
YUP! You got it!
Customer: replied 3 years ago.
i ant find the plug to put the jumper it aint under the dash on driver side
Expert:  Amedee replied 3 years ago.
It should be under the dash on the drivers side. Look towards the center of the vehicle under the dash and then over to the left if you do not see it.
Customer: replied 3 years ago.
its not under the dash anywhere
Expert:  Amedee replied 3 years ago.
Ok... no problem.

You might just have a bad distributor or maybe the o2 sensor or map sensor is bad. Just be sure that the fuel pressure checks out ok as well as the engine coolant temp sensor.
Customer: replied 3 years ago.
thats another thing i have a two sensores in front the throdel body on top of the thermostat housing and one of them the plug is block off .but i cant match that sensure or find out what kind of sensor it is anywhere
Expert:  Amedee replied 3 years ago.
Are you saying there is a sensor unplugged up by the throttle body that you are not sure what it is?

Can you upload a picture?
Customer: replied 3 years ago.
yea but it aint a part of the throttle body and give me a min on the picture
Expert:  Amedee replied 3 years ago.
Sounds good!

Take a few pictures..
Customer: replied 3 years ago.
k
Expert:  Amedee replied 3 years ago.
I will be waiting for your reply!
Customer: replied 3 years ago.
its not letting me attach the pics
Expert:  Amedee replied 3 years ago.
The pics may be too large. Save them as a Jpeg pic in your computer and then it should work.

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