02 Burb - Replaced motor...won't start?

[mrharris32]

I'm in an interesting situation with this vehicle, a 2002 Suburban. I agreed to help a friend and swap the motor for him (original motor had 200k+ and 2 rod bearings knocking badly). I have 12 years of mechanic experience and several years of custom frame off restoration experience.

I scored my buddy a clean 5.3 with 70k miles from another 02 suburban. After about 30 hours of labor (did it all myself!) the new engine was ready to crank last night. I turned it over, oil pressure jumped right up, all looked well, engine studdered (never started), I hit the fuel purge valve on the incoming fuel line (top of manifold) to release the air. Air out..good. At this point I assumed she would fire right up...wrong. When the motor cranks it is hitting on at least a couple cylinders...sounds like it wants to start but is severely out of time...the fuel or spark is off. I confirmed the engine had spark and fuel of course. Interestingly enough during the troubleshoot I pulled the plugs, 1 was soaked in fuel, the rest were dry.

The only variables that were changed were as follows...the crankshaft position sensor connector/pigtail (back of intake manifold) broke when the motor was pulled. I replaced it with a new pigtail and used the wiring diagram found in the Chilton's for 2000-06 Burbs, Tahoes, 1500 pickups. Also, the driver side head has 1 bolt that was snapped off (exhaust manifold mount) when the salvage yard took the motor out...so it does have a tiny exhaust leak..nothing that should prevent a start however. I will note however the plug that was soaked in fuel was aligned with where the leak is.

I put a scanner on, pulled no codes. Questioning the new pigtail I pulled the plug on the CPS, and immediately got a low code for the CPS...making me more sure the wiring is correct?

I'm not sure what to do here, did I miss a pre start step? Is the PCM retaining old information (had no voltage for 2 weeks)? Could there be air in the fuel rails at the injectors preventing a start? Being the LS there's no way for me to manually adjust the timing without a more expensive scanner...and even so that shouldn't be necessary? ANY help would be appreciate here, 12 years of wrenching and I've never been so stumped.

On a final note the Security light comes on when I open the door flashing, it turns off when I turn the key forward or shut the door...it's not the typical Chevy security issue (i.e. turn the key and nothing happens). This may just be normal?

Thank you in advance!

[PitchBlackC3]

What is the fuel pressure?
Did you reuse the original intake manifold & injectors or did these come with the new engine?
Check the grounds on the back of the heads, one on each side.

[mrharris32]

I will check the grounds again, I did put a jumper on the primary ground last night to ensure solid connectivity with no response. As I recall I had one ground strap on the passenger side (bolts to one of the tranny bolts), and then 1 heavy gauge/1 smaller gauge ground that bolted to the lower block on the driver side.

I have not yet checked the fuel pressure, it is strong at the incoming line purge valve. The intake and injectors on the motor now are the ones that came on the new engine, I did swap the coil packs (the ones on the new motor appeared to have been exposed to heavy moisture). Thank you for your response. I've yet to be defeated on a repair/swap...this will not be the first one!

[classic1]

It's probably the VATS or Vehicle Anti- Theft System. You or someone with the ability needs to unlock it. I did a swap into my 92 and had the same problem but once I unlocked it with HP tuners it fired right up.

[George C]

vats shouldnt do anything if its a replacement motor in the same vehicle


that isnt the crank sensor in back of intake its teh cam sensor and if you messed this up it wont run right. it would also throw a code asap if a wire is wrong somehting along the lines of high Freq

[Mr.Cornelius]

Hey guys im having the EXACT problem with the same issues can anyone PLEASE Help..

[truckinL33]

I don't know exactly what you did during the swap, but I would put the cam sensor from your buddies old engine into the new one and see what happens. The way you describe that cylinder 1 is soaked but the rest are dry, this may be because the cam sensor is damaged or something. It's free to do, and relatively easy. Furthure more, that exhaust bolt that broke off is common. It also happens to be on cylinder number 1 that it happens to. This is why I am assuming that cylinder number 1 is your fat cylinder, which is also why I am considering your cam sensor to possibly be faulty.

[oleshifty]

02 also had option of normal or flex fuel. It is possible the injectors on the NEW motor are a different size then his old motor. I would assume this would still start, but run pig rich, but it's hard to tell. I THINK the flex fuel injectors have a different plug, so it may not be possible to hook up wrong ones. Obviously make sure the coil packs are hooked up correctly on both sides. All injectors are plugged in, etc.

I would think a cam/crank sensor would throw a code immediately, but if you have spare parts laying around, won't hurt to throw them in and see if anything changes. They are just magnets. If motor sat a while, might be tarnished up and not reading correctly.

[Mr.Cornelius]

Thanks guys for the suggestions, Im going to try everything tonight. Would a cracked oring in the fuell supply or return line cause it not to fuel? It runs perfect when i spray fuel into the throttle body. IDK what to do I need my truck

[oleshifty]

If you have fuel at the schrader valve on the rail, it's probably hooked up right.


Double check the main injector harness, and make sure each one is plugged in all the way. If it 'runs perfect when you spray fuel in the tb, it's not a timing issue. It's a plastic intake that is only supposed to carry air, I'd be careful with that, good way to backfire and blow intake off. I'm assuming you have intake off, have you tried running it with the maf and everything hooked up? My truck doesn't run with the intake tube off the TB and nothing is wrong with it