4.8M37

What would cause this condition? Engine is a 4.8 from 2004 express 2500. using stock PCM(Not reprogrammed yet), trans, harness, ign switch and key, fuse blocks (underhood, and body), and BCM. Also running stock fuel pump and corvette filter/reg(60 psi when cranking). I have spark, but no inj signal (checked with noid lite). I do have full batt voltage at inj. ABS, Evap, and airbag wiring has been removed from harness. The only DTC showing was fuel tank pressure out of range, and that was only a pending code. Any thoughts on where to look next????

Thanks
Brett

4.8M37

Hasn't anyone got any ideas, I'm pretty well stumped.

Thanks,
Brett

nunan0219

iTrader: (2)

possible ckp issue? or even cam sensor issue. check to see if your getting any voltage signals from the cam/crank sensors while cranking. without them you wont have an injector pulse.

Jones'n

You answered the question in your first post.
"using stock PCM (Not programmed yet)"

The computer needs to be programmed and the VATs turned off. The ant-theft system in these computers disables the Injectors.

nunan0219

iTrader: (2)

i thought it would fire up and than shut off after a second or two.

4.8M37

There should be no issue with VATS this van did not have it. Plus I'm using the Van harness, Ignition switch, and Key.

Will an issue with the cam or crank sensor not fire the injectors but still have a spark. I haven't look too deep into those issues, because I thought it needed both of those to make a spark as well.

I'm not really ready to run the truck yet, Its just I'm far enough along that I really wanted to start it for motivational reasons.

I'm thinking the best thing to do is put aside my desire to hear it make noise, keep working on the truck, and find some one to tune and check out the PCM. There's a side of me thats thinking the PCM may be bad.

Who would you guys recommend for tuning? I'm not really looking for performance gains just deleting emmisions etc.

Thanks Again
Brett

nunan0219

iTrader: (2)

check all of ur grounds, make sure theyre all connected.

id check the ckp and cmp sensors just to be on the safe side.

jefferyallison

I recommend Sinister Performance (http://www.gmtuners.com/) Ryan has done a couple of reprograms for me and is extremely helpful. Note: He only works through email, but he does respond quickly.

gMAG

iTrader: (1)

Do you have a schematic? I couldn't find one online unless I 'signed up'.
Find all of the pins on the end of your wire harness connectors which should have grnds. Verify that they are grounded.
The ECM ckt which controls the rotating (firing ord) grnd which controls your spark should be the same ckt which controls injs. If coils work, then injs should work.
However, I'm thinking that the grnd which comes from the BLOCK TO ECM for COILS might be separate from the grnd from the BLOCK TO ECM for INJS. I don't know this for sure.
Does a 4.8L have two cylinder banks? If so, I might check for inj (noid) on a cylinder in each bank.
As mentioned above, verify the 3 leads on your CKP harness for continuity, & verif if they have grnd, 12v?, & control voltages. Again, if you already have spark, I would think that inj should be OK as well.
Unless I've misunderstood your comment, a tuner won't be able to solve your problem, other than to lend you advice.

4.8M37

Thanks for the help with this guys.

I've been out of town for a couple of days so I haven't been able to do much. As far as grounds go. I have diagrams and pinouts from alldata, and i've already verified all the grounds at the pcm with a voltmeter. I've checked 2 or 3 injectors on each bank with a noid lite and get nothing. I've checked continuity between each injector and the pcm connector with a voltmeter. I've also confirmed that i've got 12v at each inj in both run and start.

I'm going to confirm everything between the crank and cam sensors and the PCM just to be sure. After that the only thing I can think to check next is the PCM. Is it possible for them to fail in this manner? I'm also assuming that whoever I send it out to for a tune will be able to check it out. Am I off on this thinking?

Thanks
Brett

SS69LS1

iTrader: (108)

I have the exact problem on my 02 LS1 motor. If I shoot some carb spray in the intake, it will run for a few secs. My vats was turned off last night. How do you check the crank & cam sensors? I have an 02 Fbody computer & speartech harness. Will keep an eye on this thread and check things out as they are suggested here. Scott

gMAG

iTrader: (1)

Brett,

This sounds correct. What I might try is this...If you still have your NOID lamp, I would pick out one lead responsible for inj pulse (cyl 1,2,3,etc,)leaving directly at/from the ECM. Disconnect the harness at THAT particular inj @ the engine. Tap into the lead @ ECM with your NOID & wire 12v to the other side of NOID & look for pulse. This may sound nit-picky, but I feel might be valuable. Then, depending upon this outcome, you can continue to the sensors. Even though you said there is no VATS, I'm wondering if there is something else on the ECM/programming which needs to be verif. Good luck!

jefferyallison

I'm also assuming that whoever I send it out to for a tune will be able to check it out. Am I off on this thinking?

When I send my pcm to Ryan @ Synister Performance, he provides me with a list of everything I want to remove and change and then he does the reprograming based on that. I don't know if he actually applies a test to the pcm but I am guessing that it would not take the reprogram if there were any problems with the unit itself.

gofastwclass

iTrader: (2)

I've never fried one of my own but the people I have heard who did had an error during reading or programming so there was a hint at disaster before the PCM was used.

4.8M37

Its alive.

I'm here to eat my words. VATS was the issue. Looking back, I'm not sure why I thought there was no vats on the vans. Any way the issue was with the fact that the ignition switch was not from the van I bought. The guy I bought the van from wanted the original column because the air bag was still good, and I didn't want it, so he gave me a column from a different van. I had forgotten all this. I just had to let the computer relearn the security signal from this switch and she fired right up.

Thanks for all your help

Brett

gMAG

iTrader: (1)

Very good, Brett.
I've had several of those "forgot I had done that" moments.
As you know, there are so many details going on, that it's easy to lose track of the context.

ponjohn

How do you "allow" the relearn?

pdsq98gt

You have to have a passlock lock cylinder with a passlock sensor in it. Turn the key on for 10 minutes, turn it off, on 10 mins, off, on 10 minutes...start. I think you also need the bcm installed.

4.8M37

You do have to have the BCM. The security programing is in the BCM. Alldata had a good run down on the procedure. It took me a while to find it though. It also took me 3 tries to get it right. the first time I read the procedure on the computer in the house and did it from memory it was so simple right, Wrong. Second time I printed it off, but got distracted doing something else and let it go too long. Third time I stole the wife's cooking timer, and everything was good. The procedure was as follows

30 Minute Learn Procedure

1)Turn ON the ignition, with the engine OFF.
2)Attempt to start the engine, then release the key to ON, vehicle will not start.
3)Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF. (I had no cluster, so I just set the timer for 10 minutes)
4)Turn OFF the ignition, and wait 5 seconds . (this is what I missed doing it from memory)
5)Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes , the vehicle is now ready to relearn the Passlock(TM) Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK. IMPORTANT: The vehicle learns the Passlock(TM) Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.
6)Start the engine. The vehicle has now learned the Passlock(TM) Sensor Data Code and/or password.
7)With a scan tool, clear any DTCs if needed. History DTCs will self clear after 100 ignition cycles.

On another note, I just realized that the 4L80E doesn't have a speed sensor in the tailhousing. Does the PCM need a vehicle speed signal in order to shift correctly? On my truck the speedometer cable is attached to the divorce mounted transfercase output. I don't think I would be able to adapt a electronic pick up to this because It would be way off when in low range. Hopefully this is not needed.

Thanks
Brett