Hi folks,

I've posted an extensive thread at S10Forum.com about this ordeal and I recieved some great suggestions but none have turned out to solve this.

Some background.. I have a 2000 S-10 pickup that had a 4.3 and 4L60E. I replaced that with a 5.3 Vortec and 4L60E from a 2000 Sierra. The only internal mods are a 2002 LS6 cam and springs. The wiring harness is from Current Performance Wiring and plugs into the stock power distribution box in the truck.

What's happening is on first crank, I get a few revs of firing/ignition and then nothing. Continuous cranking yields nothing, it just cranks with no activity. Every time i let off the key and re-crank, it sputters again for a few revs. I have HP tuners and have logged some of the important bits. After a few revs, the injector duty cycle drops to 0% and continues there until i let off the key.

Here is a screenshot of 4 distinct crank attempts.


Sometimes it'll fire for a few more revs but never gets to 'running' status. It runs longer (2-3 seconds or so) on a squirt of starting fluid but I don't have arms long enough to spray and crank at the same time.

The fuel pump is stock, and I think the check valve is dying. Prime fuel pressure is 62, and bounces between 55 and 65 during crank. It drops off quickly after the pump shuts off. I have a new pump en route. A GM tech suggested I try pinching the return line a bit to maintain some pressure, and I did, and no difference.

I have checked the CKP and cam position wiring and sensors and they are good, and brand new. I have good data from the coolant temp sensor which is new, IAT, MAP, and MAF which are reused. I have disabled VATS through HP Tuners. The rest of the tune is stock 2000 Sierra.

I have a new PCM en route as well, thinking it might be something there. I have ground straps running everywhere to try to rule that out.

Any leads would be most helpful. I can't spend any more time on it this week but Friday I plan on installing the new fuel pump and trying the new ECM.

 

Here's 1 test you can try. Grab a can of brake cleaner or throttle body cleaner and spray into the TB or vacuum port while cranking. If it starts and continues to run with brake cleaner, it's a fuel delivery issue. If it dies, it's a security issue. Get a noid light that fits your injector, and see if you have a signal during cranking, and see if it goes out when engine dies. This indicates a security issue where PCM allows cranking and fire for 2 seconds, then kills injector signal so vehicle can't be stolen.

2Barrel

 

Yes I can keep it running for a while on starting fluid. I didn't want to go too long but I ran it for 10 seconds or so.

 

" I replaced that with a 5.3 Vortec and 4L60E from a 2000 Sierra"...How long did the "new" engine sit B4 you tried to start it?
Injs fresh?
See this frequently w/ jy engines my bud sells. When I get the injs, they are frequently so full of crud, they are junk...Especially, if there's rust present.

 

The injectors are free. As mentioned in the original post they all squirt about 3 times at first crank and then there's no injector duty cycle. That is to say, they fire when they are told to, but they stop being told to. Something in the PCM is telling them not to fire after about 3-5 revolutions.

 

You need to have vats(security) disabled in tune.

 

It is set to 'none' in HP Tuners as stated in the OP.

 

Thought I'd give an update here, since I've had some time to play with it.

Got a new PCM, tried a few different stock tunes from HPT repository. No change. Rechecked all the grounds and vacuum sources and all appear ok. Pulled the injectors and fuel rails and flushed those out, they seem to be ok. I have strong spark on all cylinders. Added a VATS status bit to my HPT scan and it says 'PASS'. Replaced the cam position and map sensors. All of this and it still does the same thing. A few injector pulses and then nothing.

 

Well guys, it runs. despite my testing, it turned out to be the crank position sensor. I feel stupid for not just replacing it in the beginning, because I hate believing that brand new sensors can be bad, but this one was. Thank you for everyone's help.