please help me troubleshoot-no start 2004 trailblazer

cc2001

Original poster
Member
May 24, 2013
11
Hello everyone i was wondering if anyone could help me troubleshoot this, 2004 trailblazer LT spins but no start, i have checked the pins at the fuel pump relay and there is no power on top right relay socket, , also when i jump, top left pin socket to bottom right socket which is supposed to complete fuel pump circuit, i hear an air sound at engine but still no start, if anyone could help me go farther i would really be grateful.
 

MAY03LT

Member
Nov 18, 2011
3,412
Whaddup? That top right pin only gets power for like 2 seconds after the key is turned to "run". You should have someone turn the key while you watch the test light or whatever you're using. Since something happens when you jump those pins, something is happening with the pump. Do you have a fuel pressure gauge? If not, can you get a hold one?
 

cc2001

Original poster
Member
May 24, 2013
11
hey may03lt,
thanks for reply, i dont have a fuel pressure gauge and the only way i could get one would be buy it, i am just trying to not put a fuel pump on that is not needed, your you tube videos are great, i didnt know the power on the wire left after about 2 seconds, i followed your you tube video on how to check the fuel pump circuit and there was no power on the upper left cavity with key on. Should i recheck?
thanks
chris

is the only way to check the fuel pressure the gauge? i also meant to tell you it blows the pcm fuse #28 right when i try to crank
thanks again
 

MAY03LT

Member
Nov 18, 2011
3,412
cc2001 said:
is the only way to check the fuel pressure the gauge? i also meant to tell you it blows the pcm fuse #28 right when i try to crank
thanks again

Chris.....that changes everything. Fuse 28 is mandatory for the truck to run. That fuse is not only for one of the circuits that the pcm needs to turn on when the key is in run/start, but also for the positive side of the coils and injectors. The problem is, GM never told anyone exactly what that circuit does inside the pcm, so there isn't a definitive list of things to check. I've read cases where everything from the fuel pump to the pcm harness to the pcm itself being the culprit.

I think the first test to do next would be to remove the fuel pump relay, put in a new fuse 28, and crank the engine. We're looking to see if 28 blows again, prette much a process of elimination.

cc2001 said:
hey may03lt,
thanks for reply, i dont have a fuel pressure gauge and the only way i could get one would be buy it, i am just trying to not put a fuel pump on that is not needed, your you tube videos are great, i didnt know the power on the wire left after about 2 seconds, i followed your you tube video on how to check the fuel pump circuit and there was no power on the upper left cavity with key on. Should i recheck?
thanks
chris

Man I hear you there a good pump aint cheap lol. Based on my reply above this I don't think we have to worry about testing fuel pressure right now. But, for anyone else that might read this, a pressure gauge is the only way that I know to definitively know what the deal is. I've had more then my share of vehicles that you could hear the pump run but the pressure was 10-15psi, not nearly enough to run the engine.
 

cc2001

Original poster
Member
May 24, 2013
11
ok thanks alot
im gone go out in about 30 mins and check that fuse, like you told me, i will report back shortly

thanks!!
chris
 

cc2001

Original poster
Member
May 24, 2013
11
Hey
just tried procedure, fuel pump relay removed turned key on, fuse 28 blew immediately

thanks
chris
 

cc2001

Original poster
Member
May 24, 2013
11
Hello
i wanted to post an update on this thread
finally got the truck running by replacing #28 fuse, one finally held and did not blow, upon cranking truck is missing terribly, flashing check engine light, i failed to mention the following and a friend of mine said i should, i had just put this truck in the body shop, had the front right fender replaced, and battery ran dead in shop, body shop man said he recharged the battery and the truck would spin and not crank, truck was towed to my home, this is what led me to this update, i am not sure that something didnt happen in the body shop is why i posted the update, and help is appreciated
thanks
 

MAY03LT

Member
Nov 18, 2011
3,412
cc2001 said:
....truck is missing terribly, flashing check engine light

Just a misfire now? Cool.

Do you have a code reader or know someone who does? I'd scan for codes next. Usually I'd say take that thing down to autozone for a free scan but if you drive it with the check engine light flashing you could cook the converter.
 

cc2001

Original poster
Member
May 24, 2013
11
had truck scanned which produced the following codes

u1041 ebcm/ebtcm comm.

p300 engine misfire

p1516 elect throttle module performance

p1682 switch circuit failure

u1152 loss of acm/hblab comm.

any help on where to go from here is greatly appreciated and thanks
 

cc2001

Original poster
Member
May 24, 2013
11
Thanks
is there a way i could definitively check the switch?


thanks again
 

cc2001

Original poster
Member
May 24, 2013
11
Just replaced switch....same issue. Any further help is appreciated

thanks
 

MAY03LT

Member
Nov 18, 2011
3,412
Hey man just got your message. Did you guys clear the codes/restart truck/re-read codes?
 

cc2001

Original poster
Member
May 24, 2013
11
you mean after installing the ignition switch? if yes, then no we havent, only replaced switch

thanks
 

Ryda55555

Member
Apr 11, 2013
1,111
cc2001 said:
you mean after installing the ignition switch? if yes, then no we havent, only replaced switch

thanks

Yea i suggest clearing the codes/restarting the truck and see how it runs and what codes reappear, its pretty much a process of elimination here

Theres a possibility the garage boosted the battery by the fusebox and fried something but you're gunna have to take it one step at a time
 

MAY03LT

Member
Nov 18, 2011
3,412
cc2001 said:
you mean after installing the ignition switch? if yes, then no we havent, only replaced switch

thanks

Nah, before, but now would be a good time too. Since someone else was messing with it, who knows what they may have unplugged in the process.

Really we only need the current P codes for now. The U codes aren't necessary.
 

cc2001

Original poster
Member
May 24, 2013
11
Okay
so just to be clear, i should get the pcm reset and get the codes reread at this point... correct? Also i failed to list one code in previous post

p0106 map or Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem

I realize it could have been vital that i listed this code and am sorry i overlooked it in my notes, anyway, thought it was important so i included in this post, thanks for all the help
 

cc2001

Original poster
Member
May 24, 2013
11
finally got access to code reader, cleared codes, and only p0300 comes up, if you can direct me farther i would appreciate and thanks
 

CaptainXL

Member
Dec 4, 2011
2,445
cc2001 said:
cleared codes, and only p0300 comes up

Don't clear the codes. Disconnect the battery to erase them. There should be no codes if you disconnected the battery and then read the codes immediately after.

A P0300 mean that multiple cylinders aren't firing. Either it's a lean mixture, bad plugs or multiple bad coils. But now that you have cleared the codes we won't know what coils were misfiring. I would do a compression test and vacuum test next.
 

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