2006 TB - engine cranks for a long time before starting

mike_new

Original poster
Member
Aug 17, 2019
3
alabama
I'm the original owner of an 06 trailblazer with a 4.2 engine and i have to pat the gas pedal to start the engine. The vehicle has 290K miles and 2 weeks ago the fuel pump was replaced (not failed) as a precaution. The engine starting problem has been going on since before the fuel pump was replaced. I've replaced both solenoids (the one near the tank and the one on the engine) in the evap system. There was a p0171 code and I replaced the MAF. Code cleared. Throttle body is now clean. The car starts up perfect every time I do the previously mentioned changes. I need some solid advice. Thank in advance.
 

mrrsm

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Oct 22, 2015
7,639
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Welcome to GMT Nation...

To get you 'Off to a Good Start...' (pun intended) Please visit this next link and Download the GM OEM Full Digital Service Manual (Courtesy @Mooseman) and follow his Instructions to single out and obtain the one for your Particular SUV. This Reference Guide (PDF) is the Compass necessary to Guide you through the "Crank- No Start" issues and the related "No Start-No Crank" problems bu following the Diagnostic Trees covering these Issues.

Having a Good OBD2 Scanner, a"Scope on A Rope" Lighted Continuity Probe and a Decent Digital Multi-Meter along with a Fully Charged Battery offer much assistance as you to try to run each problem 'To Ground". The Chapters in these REAL Service Manuals make the other "Repair Books" look like Thumb-Nail Sketches on the back of a Party Napkin.

Remember that your 'underhood' Power Distribution Center...with various Fuses and Relays along with the Fuses/Relays with the BCM under the Left Rear Seat are often the Best Places to Check First once you examine their 'undercover' Lids for the #s and Locations of the ones you think are related to the problems:


These Three Diagrams cover the Ignition-Starter Circuit and the Fuel Pump (Two Separate Diagrams) that can help you with Diagnosing the Circuitry and Components that begins with 'The Turn of The Key"...and everything in between that can go wrong to stop the Engine from Running Right. Please Post ALL of the GM Codes you are able to Read on the OBD2 Scanner ...and Remember to take them in their Order of Appearance to obtain the Best Solutions:

TRAILBLAZERFUELPUMP.gifTRAILBLAZERFUELPUMP1.gifIGNITIONSTARTERCIRCUIT.gif
 
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gmcman

Member
Dec 12, 2011
4,656
The car starts up perfect every time I do the previously mentioned changes

Are you referring to having to pat the gas pedal?

Can you confirm you don't have any vacuum leaks?

Air filter clean?

How old are the spark plugs... mileage on plugs?

Does this happen on cold starts only or everytime?
 

Maverick6587

Member
Dec 16, 2018
730
Sterling Heights, Michigan
Do you have any CELs on your dash?

I had a similar issue that was solved by replacing the crankshaft position sensor and running a crank relearn with a Tech 2. It would take a second or sometimes two seconds of cranking to actually start the vehicle.

You may also want to inspect and clean your camshaft position sensor, crankshaft position sensor, and the VVT solenoid. Make sure that you use a flashlight and inspect the area where the plug plugs into the VVT solenoid (where the two/three prongs are). If you see ANY oil at all. Replace the VVT solenoid, as it is bad/going bad.
 
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mike_new

Original poster
Member
Aug 17, 2019
3
alabama
I’ve learned that the problem goes away if you turn the key on and let the fuel pump build pressure.So, I believe the new fuel pump is not holding pressure. That tells me the check valve is leaking by on the discharge line.
 

Maverick6587

Member
Dec 16, 2018
730
Sterling Heights, Michigan
@gmcman had some good questions for you.

What brand of fuel pump did you use?

After you cleaned the throttle body did you disconnect the battery for any period of time? It will need that so that it can run it's relearn procedure.

Also, referring to my post #4. I had the same thing happen to me as you mentioned in your post #5. If I let the fuel pump fully prime vehicle would start almost right away. It would still be milliseconds off from perfect but it was close. As soon as I did the crank (CASE) relearn it started perfectly.

I would have thought they (fuel and crank) were completely unrelated but, it worked in my case.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
You should do a fuel pressure check and see if it's within spec, that it holds that pressure for a while after priming and that the pressure is also within spec while running.

*** Please be careful when attaching the pressure gauge's hose to the valve on the fuel rail. It's in an awkward position and any strain on that valve WILL crack the rail. Ask me how I know.
 

mike_new

Original poster
Member
Aug 17, 2019
3
alabama
The mechanic used a delphi. I always disconnect the negative cable. All seems good now and I’m going to take it back to the mechanic for the pressure test. Full disclosure-I’m not physical able to do some work I once did so I shelled out 8 Benjamin for the fuel pump.
 

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