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Canuck Tech
Canuck Tech, Auto Service Technician
Category: Car
Satisfied Customers: 524
Experience:  Red Seal Journeyman Technician, 20 Years experience
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gmc sierra: I have a 2000 gmc 1500 5.3 167,000 miles. I have

Customer Question

I have a 2000 gmc 1500 5.3 167,000 miles. I have a problem with it stumbling mostly after a restart: Ex: runs fine when first started in morning, but if you go for a short drive shut if off then start it again it will stumble and hesitate with no power under load, until the gas pedal is released for a few seconds, then it clears out and runs alot better, and the more short trips i do the worst it gets. started doing this at around 100,000 miles. replaced plugs, wires, fuel pump, fuel regulater. no codes
Submitted: 1 year ago.
Category: Car
Expert:  Canuck Tech replied 1 year ago.

It sounds to me like there is a fuel issue - what I mean is that I suspect the fuel pressure is leaking down - after a hot soak. Do you have access to a fuel pressure gage? Because you have already done the fuel pump and regulator, the gage is going to be a necessity to check for leaking injectors. Put the gage on, close the hood and get the engine good and warm, and then see how long it takes for the fuel pressure to leak down. Leaky injectors cause a few problems. 1. the hard restart you have described. 2. washing down of the cylinder with raw fuel - removed the small amount of lubrication that needs to be present 3. the fuel now boils in the fuel rail, and vapor in injected into the other cylinders. So you have rich cylinders with the leaking injectors, and the rest of them are lean.

 

Engine doesn't start well hot... I would be looking at fuel pressure, and the possibility of leaking injectors. Please do not run out and buy a set of injectors. Diagnosis is required. If you do go down the injector road, get good ones, not remanufactured. I have had no luck with remanufactured injectors.

 

Best, Canuck

Customer: replied 1 year ago.

it starts just fine and idle's. Its when you take off that is when it starts to stuble and will keep doing it until you let off of the gas pedel for a few sec then get back into the gas it will come out of it. The only time it will not do this is when i run it for a long time, then it will run pretty good. I checked the fuel pressure and it was 52 psi at idle. I had it good and warm. it took about 25 min before it dropped below 50 psi. any another ideas??

Expert:  Canuck Tech replied 1 year ago.
OK - have you tried cleaning the mass airflow sensor? There is a special solvent for this purpose. Get the right stuff at the parts store. Look for any crushing of the intake tubing that could cause an air leak that the mass airflow sensor is not measuring
Customer: replied 1 year ago.

I did clean the MAS about two years ago, I will try it again, I have never check the intake tube, I will go give that a look. another thing to run by you is it seems to be worse when it has sat outside in the rain or when is really damp

Expert:  Canuck Tech replied 1 year ago.
The weather-related poor running often points to the spark plug wires, but it seems like you have those covered. Regarding the MAF, there are customers that I see once a year to clean it, and the symptoms are the same as your truck. Hopefully, this is an easy fix, and inexpensive. Wouldn't that be great!!!!
Customer: replied 1 year ago.

K I cleaned the MAF and the intake tube look good. Now it will be a little while to see if it worked. and yes that would be great!! I have been putting up with this for a long time. It is so dam hard to fix somthing when it will not break. Another thing this truck will do, if the battery ever goes dead or I disconnect the battery I have a hell a time getting it started again. I have to hold gas petal down and when it starts it have to fether the petal for about 2 to 3 min before it will stay running. This truck has me fooled

Expert:  Canuck Tech replied 1 year ago.
The battery disconnect thing is indeed strange. Do you have access to a scan tool? I would be curious to know what the "Fuel Trim" numbers are, short and long term at idle. Let me know if the MAF cleaning works. Cheers, Canuck
Customer: replied 1 year ago.

Yes I have elmscan 5 on my labtop. I will hook it up tomorrow and I will let


You know the number

Expert:  Canuck Tech replied 1 year ago.
Ok!
Customer: replied 1 year ago.

Got the numbers.


Short term fuel-bank 1 -1.6%


 


long term fuel-bank 2 -9.7%


 


I think these are the averages.


 


I'am also going to "TRY" to send you a recording numbers in microsoft excel.... Nope dont look like I can get them to from here

Expert:  Canuck Tech replied 1 year ago.

Good day, the fuel trim numbers are not holding any clues for the battery disconnect issue. Has the starting issue been resolved?

Customer: replied 1 year ago.

no change after cleaning the MAF. I did take off the throttle body and cleaned it really good and took it for a drive and it seemed to be better. I was thinking about trying some seafoam, what do you think??

Expert:  Canuck Tech replied 1 year ago.
What type of spark plugs are you running? I recommend running AC Delco, gapped to .045. The spec says .060, but that is too much. There even was a bulletin on it. I know some people swear by seafoam, but I don't have any experience with it.
Customer: replied 1 year ago.

I think they are champion's.... but not 100% I will take a look. I think i'am going to get know plugs and wires just to see. going to try ac delco and see what happens. So what do you think I should be focusing on, fuel, air, spark or a sensor?

Expert:  Canuck Tech replied 1 year ago.
The intermittent nature of this problem is going to drive us both nuts! The spark plugs are an easy start - sort of my square 1 place to start. You have covered fuel pressure... did you toss a fuel filter at it when you did the pump? By the symptoms, it appears the engine is going lean... Injector cleaning might be a good option as well. I'll do some more digging.
Customer: replied 1 year ago.

going to start with seafoam. I'am also going to rig my fuel pressure gauge so I can see it while iam driving to see if the pressure changes when it stubles. I have changed the fuel filter with no luck. I do know that I'am just going to have to spend some money to finger this out.

Expert:  Canuck Tech replied 1 year ago.

The recommended spark plug is part # XXXXX pregapped at .040. It is an iridium tip plug, so the price will get you attention, but I think the key with this problem might be with injector cleaning. GM's recommendation is a can of this stuff at every oil change - part # XXXXX 20 oz bottle - AC Delco number - treats 20 gallons of fuel or 10-3004 treat 12 gallons of fuel - basically on once of this product per gallon.

 

Sea foam might be a good option... although I have no experience with the stuff.

 

With this type of driveability issues, it is tough because there aren't many clues, like a trouble code!

Expert:  Canuck Tech replied 1 year ago.
I like the fuel pressure gauge idea - I've done that a few times and have caught some issues that way. I would go down the injector cleaning road...
Customer: replied 1 year ago.

K that is what I will do. I will let You know what happens. If I rate your service will it close this chat session?

Expert:  Canuck Tech replied 1 year ago.
You can rate and close, but we can still carry on the conversation - no problem. When we continue to chat back and forth, just don't hit "Accept" again, because then you will be paying twice. Cheers, Canuck.
Canuck Tech, Auto Service Technician
Category: Car
Satisfied Customers: 524
Experience: Red Seal Journeyman Technician, 20 Years experience
Canuck Tech and 15 other Car Specialists are ready to help you
Customer: replied 1 year ago.

Thanks for all the help!! I will get back to you

Customer: replied 1 year ago.

the spark plugs I have are BOSCH PLATINUM HR9LPX GAP .60 Do you think that could be the problem?? Once I really start thinking about it all these problems started not to long after I put these in. It ran really good before I installed these plugs.

Expert:  Canuck Tech replied 1 year ago.
Entirely possible. I don't want to run down Bosch - they work in European cars, but in my Chevy... AC Delco. I have run into problems with other plugs, honestly. Go with the recommended plugs, and let's see what happens.
Customer: replied 1 year ago.

I will do that.

Expert:  Canuck Tech replied 1 year ago.
Ok! Let me know how it goes. Canuck

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