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Discussion Starter #1 (Edited)
Hey guys new to this forum, I usually don't have to ask questions. but looking for some hints/tips, with this truck. I bought this 2004 Colorado for my son it has the I5 3.5 motor, the old one ran fine, it had 230+k miles on it and was wore out. Thought it would be a good father son project to put a new motor in.
We did a refab motor from autozone, the swap went good, no abnormal issues (i've done this a few times, not a complete newb). We didn't do any mods either, just old motor out new motor in. We got the new motor in, the motor turns over but no ignition.

On install we replaced the alternator, crank position sensor, double checked all the ground leads and connections.
It's getting fuel pressure, though not sure how to check fuel injectors are firing since they are burried under the intake manifold.

I pulled the codes, but nothing, though I'm not sure it would through any codes until it actually starts.

The only sensors I know of that will flat out keep it from starting are the crank position sensor and cam position sensors. We will replace the cam sensors today.

I'm looking for any other insight as to what could be keeping it from starting.

Thoughts?
 

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CALI BOSS
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You can test fuel pressure at the throttle body. There aren't any hidden injectors. Check for spark by pulling a coil and attaching a plug and grounding it. You should be able to smell fuel at the tail pipe if you've cranked it over several times
 

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You didn't make it clear, but I'm assuming that the replacement engine is a 3.5. Was it purchased as a short block or long block? Do you know for sure what year truck the engine came from? The fuel system for the 2004-2005 is a "return" system, the 2006 is not. You said "no ignition", but it appears that you haven't ruled out either the ignition or fuel system yet.

A simple engine swap shouldn't have any effect on the security system, but is the PassLock light flashing when start is attempted?

Have you tried spraying starter fluid or brake cleaner into the throttle body?
 

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Discussion Starter #5
Thanks for the quick responses.

It was a complete long block 3.5L. The truck is an 04, the refurbished motor is an exact match with the one I pulled out, so I'm thinking it was factory.

I did the newb thing and completely skipped the check for spark and fuel. I automatically went to the idea it wasn't getting spark. I was wrong. I went back and checked for spark and dumped starter fluid down the throttle. It's not getting fuel, it will run-ish on starter fluid.

I am getting 50psi at the fuel rail. My current theory is the injectors aren't receiving a pulse. I checked all the fuses I could find in the box by the battery. Are there others in another location? I changed a few and swapped some off the relays around, but nothing worked from that.


I tried to put a multi meter on the main injector harness plug (flat connector back side of valve cover) for the electric signals, but not sure the deflection would register on a digital meter.


My next try is to put a signal to each injector and see if it will dump some fuel to the intake. Anyone know what the voltage requirement is for these injectors?


If that works then it must be a fuse, a bad wire/connection in the harness or the PCM? Anyone have any additional thoughts?
 

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Need a GM tech 2 or similar expensive diagnostic tool. Usually engine will still start and run even of a relearn is needed but will throw a code
 

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Are there any warning lights on when attempting to start?

Usually all warning lights will light up for 2 or 3 seconds then disappear. Is this happening? If it is are there any warning lights that stay lit like the passlock/security light?
 

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Discussion Starter #10
no lights that I can tell. granted the idiot that owned the truck before me did cut the wire to the "check engine" light, but I believe that's the only one, that has been messed with. and I have a scan tool to keep an eye on the codes. But to this point there hasn't been any codes...
 

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But do all the warning lights light up for a few seconds when the key is turned to the on position?

The fact that wires have been cut is concerning, there is a passlock cheat/bypass that involving cutting a wire but when the battery is disconnected it causes starting problems when the battery is reconnected. Maybe the previous owner did this?
 

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Passlock is one of a few factory security systems that GM has used over the years. When passlock is triggered the starter will crank but no fuel pulse is sent to the injectors. Usually the passlock light will flash on the guage cluster when attempting to start then stay lit solid after. But if wires have been cut... who knows?
 

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You can test fuel pressure at the throttle body. There aren't any hidden injectors. Check for spark by pulling a coil and attaching a plug and grounding it. You should be able to smell fuel at the tail pipe if you've cranked it over several times
Fuel pressure is checked at the fuel rail. The throttle body just controls air flow. No fuel goes to the throttle body
 

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no lights that I can tell. granted the idiot that owned the truck before me did cut the wire to the "check engine" light, but I believe that's the only one, that has been messed with. and I have a scan tool to keep an eye on the codes. But to this point there hasn't been any codes...
The wire to the IPC, that turns on the "check engine" light, is the Serial Data Bus. If that was cut, there would be other problems. Can you identify which circuit has the cut wire? Have you tried connecting that wire?

Did you ever determine if the PassLock light was flashing during start attempt?
 

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Hmmm... well you can try doing a security relearn. You can do it yourself it takes about 30 to 40 min just make sure the battery is fully charged or hooked up to a charger. It requires cycling the key to the accessory on position and leaving it there for 9 or 10 min, I think you have to do this 3 or 4 times. I'll try to find the procedure.

Or you can take it somewhere that has a high end scanner that can read bcm codes. Most store bought readers can only read engine and maybe abs codes.
 

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Discussion Starter #19
yeah problem with taking it anywhere I need a tow truck...so if it comes to that it's either going to the shop or a dump.
 
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