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With a crank-no-start I often resort to a quick (no more than 2 seconds) spray of starter fluid to the air filter then crank and see if it at least sputters. That would prove at least some spark and maybe a lack of fuel. Have you examined the fuel injector wiring harness? I have seen a couple of owners have some issues with degraded wiring at the connector near the rear of the engine under the resonator.
Per TJBake post is a great idea with starter fluid. Mine acted the same way and found a mouse/Squirrel chewed wires on top of the engine going to injectors. Resolder and all is good.
 

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White 2002 Trailblazer EXT; Dark Charcoal/Green 2005 Trailblazer EXT
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Per TJBake post is a great idea with starter fluid. Mine acted the same way and found a mouse/Squirrel chewed wires on top of the engine going to injectors. Resolder and all is good.
In January, those pesky varmits built a nest under the "air resonator" over my 02 TB EXT 4.2's coil packs and proceded to eat the insulation off of 4 inches of the harness and one of the wires at the back top of the engine just in front of the quick connect. I went to a wrecking yard and got a short section of wiring and the connector and patched it in. I took that crappy box off and built a new pipe to go between the air filter assy and the throttle body so the rodents won't have a place to hide. I'm going to do the same pipe mod on my 05 when I get a few minutes.
 

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I have a 2003 Trailblazer 4.2L that will crank but will not start. It will turn over all day long, but it seems like it isn't getting fire.
I ran diagnostics on it and it threw a couple of codes: P1515,P1516, AND P0107. The first two have to do with the throttle body and the last one has to do with the Map sensor supplying too few votes to the ECM.
I replaced the throttle body with a brand new AC Delco one and it stopped showing P1515 and P1516. I tested the map sensor and it appears to be fine. My test was as follows:
Using a multimeter on DC Volts, I tested the gray wire and it showed 5 volts (black lead was grounded to negative battery terminal). Next, I tested the ground by touching the red lead to the positive battery cable and the black lead to the orange/black ground on the map sensor and the multimeter read 12 volts. Finally, I tested the voltage on vacuum and the voltage dropped as vacuum was applied.

If the MAP sensor is good, why am I still getting the error code and the engine still isn't starting?

All of that being said, when it turns over, it really seems more like it isn't getting fire/spark, but I'm not getting any codes for coils. I tested the coils just to be safe and they're all working as they should be. Plugs appear to be fine, as well...

I thought perhaps it could be the ignition control module, but, from what I understand, that's built into the coils on these vehicles.

Overlook my terminology. I'm anything but a mechanic and could use all of the help y'all could give me to help me figure out what the heck is going on.

Oh, and, for the record, the fuel pump is running, new fuel filter, fuel pressure gauge read 50 when testing, I tested fuel pump relay and ecm relays/fuses and they all appear to be fine, too.

Could it be that I need a new ECM?
Have you tried unplugging the MAF and try to start it? If it starts, then you have the culprit
 

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2004 chevy trailblazer_ls_ext
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Per TJBake post is a great idea with starter fluid. Mine acted the same way and found a mouse/Squirrel chewed wires on top of the engine going to injectors. Resolder and all is good.
Yea, the tree rats did a number on the wiring harness next to the steering column on the wife's '06 TB last year! A local shop fixed the damage, cost us about $350! The rodent's really decimated the harness, though, so for the amount of damage that had to be fixed it wasn't too bad. The shop said that they do that repair all the time. I don't mean to sound like I dislike squirrels. Baked in cream of mushroom sauce they're actually pretty tasty!
 

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Discussion Starter · #65 ·
I haven't forgotten about y'all. I originally ordered cheaper coils from Amazon that were due to arrive this past Wednesday, but I read reviews where people were getting sets of 6 and only 3 or 4 of them working, so I cancelled that order and ordered Delphi coils.

They shipped this morning, so hopefully I'll have them some time toward the first of next week.
 

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I haven't forgotten about y'all. I originally ordered cheaper coils from Amazon that were due to arrive this past Wednesday, but I read reviews where people were getting sets of 6 and only 3 or 4 of them working, so I cancelled that order and ordered Delphi coils.

They shipped this morning, so hopefully I'll have them some time toward the first of next week.
Sounds like you might have this figured out...
I had a crank no start problem a couple of months ago. Drove me nuts! Finally found fuse 28 (15 amp) for PCM1 was blown. Replaced it and it kept on blowing. I did some internet research and saw it was somehow related to the fuel pump. Cleaned up the ground to the frame which looked like it went to the fuel pump and yay! Problem was gone.
There are so many inter-related circuits with cars these days that a symptom here can be related to something which seems totally unrelated. BTW...my vehicle is a 2004 GMC Envoy.
 

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Discussion Starter · #67 ·
Alright fellas..... Coils arrived today. Already installed them and turned it over and it started right up, but it's raining rough.... Really rough and my check engine light is flashing. It isn't showing any codes.
A quick Google search basically said "cut it off immediately". I'm gonna have to research what would cause a flashing check engine light, but, at least, it starts and runs, now.

Y'all got any ideas?
 

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Discussion Starter · #68 ·
Alright fellas..... Coils arrived today. Already installed them and turned it over and it started right up, but it's raining rough.... Really rough and my check engine light is flashing. It isn't showing any codes.
A quick Google search basically said "cut it off immediately". I'm gonna have to research what would cause a flashing check engine light, but, at least, it starts and runs, now.

Y'all got any ideas?
Decided to run some seafoam through it today just to see if it seemed to help at all. It didn't.... However, after running for a while, the check engine light stopped flashing and remained solid. I checked for codes once again and I had p0300 random/multiple cylinder misfire.

Now, I'm trying to diagnose that. It's still idling rough. I'm determined to get this thing going again.

Anyone got any ideas on where to start?
--Coils are new (didn't test them before installation, but highly doubt Delphi sent me a bag coil)
--plugs are good (all tested for spark and gap before installation)
--gas in it is new, fuel filter is new...
 

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2004 GMC Envoy SLT 4.2
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Seafoam can do wonders , but , not instantly . If you're gonna try it , give it a chance , like a tank full , at least .
 

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Dtharp
You mentioned you checked the spark plug gap. With the irridium plugs that can damage them, A/C Delcos are pre gapped.
 

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Discussion Starter · #71 ·
Dtharp
You mentioned you checked the spark plug gap. With the irridium plugs that can damage them, A/C Delcos are pre gapped.
Yeah I checked them by firing each one individually while connected to a coil and turning the engine over.

Last night about 7pm, I went ahead and replaced all 6 plugs with brand new AC Delco iridium plugs. Put everything back together, started it and I noticed the radio wasn't on and the interior lights were flickering like crazy. It's been so long since I drove it that I forgot it did that before. Now, I'm wondering if I might have an electrical problem somewhere that would somehow cause the coils to short out.

I have a new battery, all new coils, all new plugs, new fuel filter, 50psi fuel pressure, thoroughly cleaned throttle body, new map sensor and I still have a rough idle, code p0300 (random/multiple misfire) and the return of flickering interior lights and a radio that doesn't come on.

Any ideas?
 
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