4.8 Truck norris cranking with no start

[Mike Heyboer]

Hello,

I am very new here and definitely a novice to tuning as I have only messed around with a couple cammed silverados. I just finished up putting together a 4.8 with a truck norris cam, pac 1218 springs, 77lb decapped injectors that were all flow matched to within 2%, gapped rings, trunion upgrade, and a 7875 turbo. I am really struggling getting this thing to fire off and I am sure I will be getting some heat over the fact that I am using decapped injectors. The engine is cranking but will not fire off...the best result I can get is some flames coming out of the headers. I have verified that all injectors are spraying properly and the rail is maintaining 58lbs of pressure on the stock vacuum referenced regulator (return style system). We have also added a gm style flex fuel sensor and have copied all data to the 2002 tahoe flex fuel tune (Changed the vin on the flex fuel tune to match my own data and disabled vats). I will post a log of the vehicle cranking...i'm sure I am missing some essential PID's that could be useful so any advice there would also be appreciated. I am also attaching the tune file for the stock unit so that you may compare to my current tune to see where I am going wrong.

[gtstorey]

So to recap:

Decapped injectors so no real tuning data so no way of verifying " that all injectors are spraying properly".

You modified a file from another vehicle and wrote that file to your ECM instead of modifying your existing tune to match the desired tune?

[Mike Heyboer]

Sorry, when I say they are spraying properly I mean they are all visually working when the car is cranking lol. Correct, if I could have integrated a flex fuel sensor with the stock file on my P01 ecm from a 2002 silverado I would have but those tables are not available. This is why I pulled a p01 2002 tahoe flex fuel tune off the repository, unlocked my stock tune and the tahoe after changing the VIN and disabling VATS. As far as I know, that is the only way to run e85 on this setup and I have read about a lot of people doing this on these forums.

[gtstorey]

The writing of the other tune may work on these. I can't keep track on what you can do this on.

[edcmat-l1]

I would unplug all the injectors, pull the plugs and check to see how wet they are. Crank the engine over with all the plugs out of it to get all the fuel out. If the plugs are wet, replace them.

Then, with the injectors still unplugged, open the throttle body and spray some carb cleaner or flammable brake cleaner in the intake. See if you can get it to fire off of that first. If it won't you know there are other issues.

Those early year LS engines, you couldn't swap the coil packs from side to side. They're wired differently. If the engine is from a 2002 Tahoe like the PCM says it is, you need to pull a wiring diagram and make sure the coils are on the correct sides.

[Mike Heyboer]

I can always go back to the original tune and modify that for now but I don't think that is the issue here. Would you mind taking a look at the log that I posted and see what is going on with the cranking situation? I am mostly concerned with how low the commanded AFR is while cranking and my injector pulse average for each bank...i'm unsure of what these values should be on any setup to be honest.

[Mike Heyboer]

Okay edcmat, thank you for the advice... I can do this on friday morning and post an update on what I find. I didn't know that this could potentially be an issue when doing a complete swap and reworking a harness on these early gen 3 engines, i'll check the coil packs when I get off work this evening. I appreciate the input!

[edcmat-l1]

I can always go back to the original tune and modify that for now but I don't think that is the issue here. Would you mind taking a look at the log that I posted and see what is going on with the cranking situation? I am mostly concerned with how low the commanded AFR is while cranking and my injector pulse average for each bank...i'm unsure of what these values should be on any setup to be honest.

Put your laptop away. Stop trying to "fix" it via tuning. Clear the motor out, put fresh plugs in it, disable the injectors and see if it will pop off on spray.

Check to make sure you have spark. Your laptop won't tell you if you do or don't. You need to test with a spark tester.

[blindsquirrel]

DTCs P0101-103 are set to No Error. It must be able to set those codes for it to run without a MAF. Set those to MIL on First.

[gtstorey]

Start with edcmat's suggestions.

Probably no one has a clue what to expect for injector pulse width. "decapped injectors". What did you do for all of the other injector data other than "flow"?

[Mike Heyboer]

Thanks blind squirrel, I will get that changed...not sure why I did that. Probably doesn't help that I make most of my edits at 2 am after work lol.

[gtstorey]

Would "flames from the headers" not indicate at least some level of ignition firing?

[edcmat-l1]

Would "flames from the headers" not indicate at least some level of ignition firing?

Absolutely. Would also indicate incorrect firing order unless it took off and ran.

Even with the DTCs set to NER it should pop off and try to run. Not very well, but it'll run. The data log shows no run at all ever.

[blindsquirrel]

What table would it use for fueling if there's no MAF installed and it's unable to set a current code for P0102/P0103?

[edcmat-l1]

What table would it use for fueling if there's no MAF installed and it's unable to set a current code for P0102/P0103?

It'll still give you a shot of cranking fuel. It'll still fire off and kinda stumble.

[SiriusC1024]

Cranking VE and Prime Pulse.

[connerterry24]

Nothing wrong with decapped injectors. Ive been running them on my truck for a little over 2 years now. as long as you have a close idea of what they flow (lb/hr), you should be able to tune the VE no problem. I will attach my tune and let you take a look at it.Turbo 4.8 Tune BTR NSR cam current.hpt
My cam is a 224/230 with a 76/65 turbo so not exactly the same but a similar setup. hope this helps

[blindsquirrel]

Knowing the flow rate does not help with the offsets & short pulse adders, which are what determines if it will run nice at small pulsewidths. One person's idea of 'runs good' might be completely unacceptable garbage to someone else.

[edcmat-l1]

Nothing wrong with decapped injectors. Ive been running them on my truck for a little over 2 years now. as long as you have a close idea of what they flow (lb/hr), you should be able to tune the VE no problem. I will attach my tune and let you take a look at it.Turbo 4.8 Tune BTR NSR cam current.hpt
My cam is a 224/230 with a 76/65 turbo so not exactly the same but a similar setup. hope this helps

That tune is in open loop and the VE is um, odd to say the least. I guarantee if you put it in closed loop it would have real issues trying to idle at stoich. I would imagine you have a meth system or some other form of fuel system (secondary pump that comes on via hobbs switch). But it doesn't even look right for that situation.

[Mike Heyboer]

So I looked over the coil packs and they were definitely wired backwards...fixed that and the car fires right up. I can't put it in closed loop right now anyways since I haven't welded in my O2 bung and finished the exhaust yet. I appreciate the advice edcmat, you definitely put me in the right direction by saying to put the laptop down lol...now I can get the rest of the car finished up.