Cranks but doesn't start

tomsmith

Original poster
Member
Mar 12, 2013
30
Hi,

I've read a couple of other threads for 'crank, no start' problems but I can't seem to figure out my problem. I have a 2004 Trailblazer LS that refuses to start, though it seems to crank over pretty healthily.

I have a fully charged battery that doesn't dim the lights when I crank and there are no codes stored or pending.

I will say this .. I just finished replacing my front differential so I had to undo a LOT of stuff, but mostly mechanical, not electrical. The only exception being the A/C compressor, but I've double checked that and it's on fine, the connector is on fine and the serpentine belt is nice and tight.

The one thing that is bugging me is when I dropped the power steering rack to get the oil pan out, I had tied up the steering wheel with the seatbelt to stop it from moving. At some point, I wanted to full drain the old power steering fluid so I undid the belt and turned the wheel a couple of times both way to force the fluid out. Immediately, I thought, "I should be tracking the number of turns I'm doing" - but by then it was too late, I have already spun the wheel :sadcry:

I got the steering wheel back to center and it seemed to line up with the tires just fine .. when the steering wheel is 'straight on', the tires are also straight. However, I'm wondering if somehow, I've managed to mis-align the ignition switch with the rest of the steering system and that's why it's not starting?

When I turn the ignition on, I can hear the pump so I'm assuming that should be OK. I'm not sure of course, but the trailblazer was absolutely fine before I starting working on it, just won't fire up now :sadcry:

Thoughts? Advice?

I really, really (really), don't want to have to drop the steering rack again .. it was a LOT of hassle
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Our ignition switch is located on the steering column, but really isn't connected to the steering shaft at all. We don't have an anti-theft steering wheel lock.

Assuming you have a voltmeter, start by poking about at the ignition switch wiring if you want to feel better about it:

RED on the ignition switch is 12V, fused by underhood fuse #34, and feeds the following three circuits:

White is hot in ACCY, RUN, START
Orange is hot in RUN
Yellow is hot in START

RED/WHITE is another 12V, fused by underhood fuse #36, and feeds two circuits:

Brown is hot in ACCY, RUN
Pink is hot in RUN, START

At the same time, check every fuse under the hood and the rear seat for being blown from a pinched wire or something.

Did you download the available schematics? I'd continue by tracing the power for the coils, throttle body, PCM, and so forth. It's good to hear that you can hear the fuel pump. That eliminates a lot of items, since the PCM won't even command the fuel pump relay to run or the starter relay to spin the starter unless a lot of other stuff (including the PCM) is working pretty well.
 

tomsmith

Original poster
Member
Mar 12, 2013
30
I checked all the fuses in the engine bay and under the rear seat with a voltmeter, all of them passed.

I haven't tried the volt check on the ignition switch yet .. Will try that later as I'm having some problems getting the steering plastic pieces to separate in two.

I just want to confirm something .. when I turn the ignition key to 'ON', I can hear some whirring which I assumed was the fuel pump but now I think I might be mistaken. It's hard to tell but it sounds like the whirring is coming from the front rather than the rear where the pump is right. Unfortunately, I don't have anyone to turn the key on while I put my ear to the rear of the vehicle yet .. wife'll be home in the evening so I can try it again then.

I should expect some whirring/whining/priming noise from the rear right? That would mean the fuel pump is doing something or does it make a different kind of noise?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
After you break a tab on the ignition switch cover, you'll know where they are to push on next time. :wink:

Fuel pump is typically a couple of seconds. You can confirm it while working alone by pulling its fuse or relay, and seeing that the noise goes away. I don't know of a whirring up front before start-up. (except maybe a flutter position check on the throttle body?)
 

tomsmith

Original poster
Member
Mar 12, 2013
30
I think it's the fuel pump - I can't hear anything from it at all. I can't believe the fuel pump is bad .. it was running absolutely fine before I changed out the diff and I wasn't working anywhere near it.

I tried tapping the tank with a rubber mallet a couple of times but that didn't work.
 

tomsmith

Original poster
Member
Mar 12, 2013
30
Could you explain a bit more please? I looked at that diagram and pulled #41 relay but not quite sure which two of the 4 slots needs to be jumped. If I'm standing at the front and facing the windscreen, the slots are:

1 2
3 4

Can you let me know which of those should be jumpered?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The schematic is certainly unclear, but it's easy to figure out. The relays GM uses in those locations (the gray rectangular ones) can be rotated in their socket, so you can't put it in backwards. That can only happen if it's rotationally symmetrical.

Look on the bottom of the relay. It should be marked:

30 86
85 87

The coil of the relay is always between 85 and 86
The contacts of a normally open relay are always from 30 to 87.

That plus a voltmeter should give you the clue you need. Find which socket pin is hot without the relay in.
 

tomsmith

Original poster
Member
Mar 12, 2013
30
OK, I got it. According to my voltmeter, #2 on my diagram is always hot. I jumped #2(87) and #3(30). I still didn't hear the fuel pump prime so I tried starting it anyway, still no luck.
 

tomsmith

Original poster
Member
Mar 12, 2013
30
the roadie said:
Check resistance to ground on #3. If it's open, then the wiring to or the fuel pump itself have issues. Or the fuel pump low side connection to ground.

The resistance on #3 to a good ground hovers around 150

On my voltmeter, 1 is full resistance (e.g. the two prongs aren't touching) 0 (the two prongs are touching directly).

So .. 150 would suggest that it's not a perfect connection but that some resistance does exist. If it's 150, does that mean that maybe the wire to the fuel pump is not making a good connection? Is there a way for me to trace that back and check?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Without a scale, the reading doesn't mean too much. But at 12V, I'd expect the fuel pump to draw at least an amp or two, which should make the resistance 6-12 Ohms. If you have 150 Ohms, that's too high. See if you can find a buddy with a trailblazer to compare readings to. I suspect checking the resistance of the fuel pump at its connector would involve dropping the tank, which is 80% of the job of changing the pump.

Hey, wingmen! Anybody else got any ideas?
 

Sir ffeJ

Member
Dec 1, 2011
543
Sorry not much help here, but if your going to change the pump yourself, I did find this video on you tube.

[video=youtube;IA-p2hKeXx8]http://www.youtube.com/watch?v=IA-p2hKeXx8"]http://www.youtube.com/watch?v=IA-p2hKeXx8[/video]
 

tomsmith

Original poster
Member
Mar 12, 2013
30
Thanks guys, this is awesome.

From what I can see, the relay/fuse box side of things seems to be OK, which means the problem lies somewhere between the fuse box and the pump. Now .. while I was changing the diff and dropping cross members etc. maybe I pinched one of the power lines from the fuse box going to the pump?

I was careful when working but I also know I banged around a bit under there, especially when getting the front drive shaft off the yoke which is pretty close to the fuel lines.

I slid back under the car to see if anything was obviously amiss but it all looks pretty good. No evidence of a broken or exposed wire though, to be fair, I'm not exactly sure which wire it could be.

This is my plan of attack:

1. On the weekend, get back under the car and do a thorough inspection of all electrical wires running on the drivers side frame rail.
2. If all seems to be well, hook up a fuel pressure gauge (will rent one) to the port on the fuel filter and test pressure while jumping 87&30 and turning ignition to 'ON'
3. If there is no pressure, I'll have a go at dropping the fuel tank using that Yotube video as a guide

Wish me luck :smile:
 

tomsmith

Original poster
Member
Mar 12, 2013
30
Hey,

Quick update. If I spray starter into the intake and then start the engine, it runs for about 2 seconds so there is spark and reinforces the fact that the fuel pump is the culprit here.

I want to make an offer to the board though .. if anyone wants it for parts or to fix up and keep, you can have it for $600CDN :smile: My weekends just got busy so I won't have time to work on it and I need the garage space so rather than having the local scrapper come take it, I figured I'd reach out to the good folks here to see if they are interested.

It's a 2004 LS with 4wd and the body is in OK shape. If anyone is serious, I'll take a bunch of pics and send them along. I live in the Kitchener/Waterloo area of Ontario for anyone who is tempted :smile:

Just thought of something, if you'd prefer to swap something rather than pay cash, I might be interested. I don't want another car but maybe some tools or other workshop stuff?
 

gmcman

Member
Dec 12, 2011
4,656
Any chance you may have pinched a fuel line? I would check the fuel pressure as well before I pulled the pump.
 

tomsmith

Original poster
Member
Mar 12, 2013
30
Hey all,

Just wanted to provide some closure to this thread. I sold it to a local guy and it got trailed around an hour ago.

Many thanks for all your help and guidance .. good luck for the future!
 

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