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Amedee
Amedee, GMC Technician
Category: GM
Satisfied Customers: 24409
Experience:  ASE certified tech with advanced level specialist. Wisconsin certified emissions state inspector
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Ok so I have an 05 impala with the 3.8 motor in it and I

Customer Question

ok so I have an 05 impala with the 3.8 motor in it and I have an issue with it stalling and I have been chasing this problem for 2 weeks I am down to tracing wires now and I think I have found the problem but I cant figure out where the hell to look so parts I have replaced harmonic balancer crank and cam sensors ignition control module all coils and yet I still have the problem and the idle air control valve so it fires up then dies if I don't hit the gas and keep it running has crank sensor codes still I tested the wires and seemed ok so this is what I have come up with looking for my 5 volt reference I have 5 volts with the sensor unplugged as soon as I plug it in it has 2.5 I'm pretty shure that's not normal also has the same issue with the air temp 2.5 when plugged in and 5 when out I am assuming I have a short somewhere but cant figure out where if I unplug all the sensors still the same pulling my hair out here makes no sense even at the pcm 2.5 when plugged in and 5 when out
Submitted: 5 months ago.
Category: GM
Customer: replied 5 months ago.
o and when I got the car there was a code for a maf sensor of which someone else has replaced
Customer: replied 5 months ago.
one more thing my scanner says that the ignition control module is in bypass mode I don't think that is correct either since when scanning a 02 montty carlo same motor says yes in the same box I and when I take a reading on that bypass wire at the pcm its like 3.9 volts gahhhhhhh
Expert:  Amedee replied 5 months ago.

Hello and welcome! My name isCustomerand I can assist you with your question. Was the PCM replaced? If not, it might just be as simple as that. Especially if your loosing the 5 volt reference. You are going to want to check all powers and grounds going into the PCM first before replacing it. Also check to be sure that the 5 volt reference is not getting shorted out by any other sensor on that circuit.

Expert:  Amedee replied 5 months ago.

Some other possible causes are an air or a vacuum leak, bad or dirty throttle body, MAF/MAP sensor, fuel pressure regulator and or weak fuel pump.

Expert:  Amedee replied 5 months ago.

The sensors that share the 5 volt reference are the MAP, TPS, EGR valve and the fuel tank pressure sensor

Expert:  Amedee replied 5 months ago.

Here is a wiring diagram of this circuit.

Expert:  Amedee replied 5 months ago.

I am glad I can help!

It has been a pleasure working with you. Please dont forget to honor your good faith deposit by rating my answer as "Excellent Service" for assisting you today.

Please let me know if you have any further questions.

Customer: replied 5 months ago.
ok so I kinda answerd my own question with the 5 volt reference on the maf I tested another car today with the same results so I spent hours last night for no reason lol but this thing when I first got it would run excellent until you shut the car off once temp comes up if you shut it off is when it will not idle or start without pushing the gas pedal and holding it at idle for a few mins then eventually you vould drive it until the next time you shut it off o and I did forget to mention very very strong rotten egg smell from the cat and also black some occasionally when u rev up I assumed it was just due to the fact it wasent running correctly misfiring and all got new plugs and coils on it but I am wondering what should the fuel pressure be exactly to me it seems low most cars are 50 I have a suspicion the regulater maybe bad but cant verify no change it I pull the hose off it please help I am a chevy guy but this car man has me burnt out work all day then all night on this pos gotta side business hhaha
Expert:  Amedee replied 5 months ago.

Engine running the fuel pressure should be 43 to 56 psi.

Customer: replied 5 months ago.
why do you think it has a very strong rotten egg smell I pulled and 02 out to see if the cat was plugged made no difference
Expert:  Amedee replied 5 months ago.

This is because the air fuel ratio is way off.

Customer: replied 5 months ago.
Think I may grab a fuel pressure regulator on the way home
Expert:  Amedee replied 5 months ago.

Sounds good. Also, dont forget to check the fuel pressure regulator for leaks

Expert:  Amedee replied 5 months ago.

Hello! It'sCustomerfrom just answer.

I am just checking in to see if you need any further assistance?

Let me know!

Customer: replied 5 months ago.
ok sorry it took so long to get back with you still have the same problems things I have replaced lets start there iac maf tps icm coils cam crank harmonic balancer and as of recently the intake manifold gaskets upper and lower and still starts in the morning ok and runs fine till you shut it off and it does not want to restart and idle on its own I can give it gas and keep it running just fine as soon as I let off it dies cant for the life of me figure out why I just got my oscilloscope tonite and thought I saw a problem with the 3x crank sensor but when it doesn't wanna start its working just fine and if I keep it running its fine I am almost outa options here I have taken the throttle body off and cleaned it also
Expert:  Amedee replied 5 months ago.

Hello and thank you for that information. Have you checked the coolant temp sensor? How about the MAP sensor? Based on my experience, this is going to be a fuel delivery issue. Not an ignition system failure.

Customer: replied 5 months ago.
Coolant temp seems to be working fine has accurate readings and no irregularities with the map sensor so is this the same motor that had trouble with the timing chain camshaft sensor not reading correctly due to that little button on the gear only reason I can think of I am getting crank codes and physical it's workin
Expert:  Amedee replied 5 months ago.

So are you saying that you are getting cam/crank sensor codes?

Customer: replied 5 months ago.
just crank codes says its workin I can see it on my scope this all started after I replaced the icm then these codes came up replaced all sensors twice and checked all wiring here's the weird part I put back in the old icm no crank codes only codes for replacing the icm same overall problem tho dies after start up and warm won't idle in its own
Expert:  Amedee replied 5 months ago.

Can I get the codes stored in the computer?

Customer: replied 5 months ago.
P0385 and p0336 everytime I clear it it comes back even though visually they are working with a scope and everything every now and then I see a lil dead spot in the graph
Expert:  Amedee replied 5 months ago.

Please send me your VIN

Customer: replied 5 months ago.
2g1wh52k059280085
Expert:  Amedee replied 5 months ago.

Thank you for that information. These codes indicate an issue with the crankshaft position sensors.

Customer: replied 5 months ago.
I know this they are working just fine tho motor isn't tho stalls and jumps and jerks then runs fine for awhile replaced cam and crank sensors twice and balancer and checked wires
Customer: replied 5 months ago.
it doesn't do that when I put old icm back on just has codes for icm replaced 2 icms to I dunno what to think here
Expert:  Amedee replied 5 months ago.
Well obviously something simple is being overlooked. You need to retrace your steps. It would not throw these codes if there wasn't an issue with these sensor circuits.
Customer: replied 5 months ago.
i noticed u never answerd my question about the timing chain and gears being a problem with the signal interrupter on the camshaft i have heard that it was a big issue
Expert:  Amedee replied 4 months ago.

Hello! YES, it is same set up and yes, it can be a problem. However, this would set a code based on my experience.