no ignition trigger one cylinder
 

Hello All,

2010 Chevrolet Suburban 5.3L
P0300 & Stabilitrac, Traction Control in message center -
160 psi each cylinder,,,cept one 80 psi

Purchased this truck recently from gentleman that done a AFM delete,with an AMS Racing kit,, cam,lifters,trays,,Diablosprt Predator2 in kit
Since putting the motor back together has always idled rough,he got tired of chasing it,,decided to sell it,and I bought the truck as is.
Only have an entry level scanner so makes things very difficult to pinpoint problems,
1. After putting infrared heat gun on exhaust manifolds could see have three cylinders that are not producing any heat. Checked injectors with stethescope,and these three cylinders,,the injector pulse will stop for 10 - 15 seconds then starts pulsing again. Only one of the three dodgy injector cylinders are on what would have been AFM cylinders, for completeness.
2. Also, checking spark with old school inline spark checker one cylinder is never firing at all. Changed known good coil , wire, spark plug to the spot and still no fire. Checked ground,reference wire, ignition wires at coil plug,,resistance vales seems the same as known good firing cylinder. Checked the signal wire on non triggering cylinder from the ECU connector up to the coil connector,,,4-wire and has continuity.
The AFM delete was done in the ECU with the provided Diablosport Predator2

Is it possible the ECU would have a blown ignition driver on only one pin, one cylinder ? Any way of checking ECU ,each IGN pin,,for resistance to verify?

TIA

That one 80 psi cylinder tells me you need to tear it down again.

That's bizarre. Yeah, I think likely on the failed driver on the ECU. Not sure how you could check that. Probably another known good ECU?

Do the injector pulse fall off regardless of engine rpm or load?

Do you have a scope? It'd be worthwhile looking at the waveform of the crank sensor. Maybe the ECU is not firing if there's for some reason a signal that's inconsistent?

@strutaeng

Have thought about getting a scope just to try and learn something from it. That sure would tell what kind of vibes the crank sensor is sending..Thanks for idea.

this is just a stock lift non AFM cam,,,no high lift,,,,yada,,yada,,, cam,,

This happens simply idling. On cold startup,,you cant tell it is missing at all,once the rpms spools down from 1200 rpm,,it gradually starts running rougher and rougher.
The CEL will start flashing even at idle. The only fault code thrown is a P0300,,strangely enough. Really wondering if maybe the Predator2 didnt write back the AFM delete correctly,,I tried the option to set to stock tune again with AFM delete.. makes no difference at all. I got the Diablosport Predator2 with the truck. have read some odd stories on these untis when it comes to the E38 ecu in particular. Without having a spare ecu is hard to narrow things down,it goes without saying.
BTW, The low compression on the one cylinder is push rod a tad too long,hanging the intake open, ,just figured this out a couple days ago.

Aside: Wonder if one of the cheap China ECU simulator units would be able to tell anything in this situation. Dont think they actually interface with the ecu itself though?.. Just curious,more than anything.

TIA

Can write the ECU tune and maybe someone can go through it and see if the AFM was deleted from it? Or maybe on the LS1TECH website? I'm not savvy enough to know that stuff, just basic reflash on HP Tuners.

Wait, so you know why you have low compression? Doesn't that have to be fixed before fixing the misfire? I was also thinking you'd have to tear it down to figure out why you had low compression. Maybe not a complete teardown? Why was the pushrod bent? 🤔

@strutaeng

Good point on the miss. The push rod for some reason, a little too much preload..just hangiing the intake valve just a tad. Not bent.if i back off the rocker bolt half turn,am only getting 10 % leak down at this point.. Don't know why even with the low compression,,all other cylinders ignition fire ok,,and one doesn't ignition fire at all. Going to order a .25 shorter push rod,
Also, the downside is of all things. The Predator2 saves the original tune/bin file in an encrypted format, so really no way of making anything useful out of it. I didn't know a thing about these things,,until getting this old truck,honestly. Had heard of them,but never studied anything about these units. They were one of the first handheld,canned tuners,,I believe. This generation of Diablosprt product has of course been discontinued for newer genertaion tuners they provide to keep up with newer gen ECU's The Predator 2 is pretty much Gen1 era hardware.

Leaning towards a good used ECU replacement at this point.

I kinda think you have a miss BECAUSE you have low compression. Seems like the ECU senses this and maybe that's why it's pulling spark and injector pulse.

I'd fix that before swapping an ECU. You need to fix the low compression no matter what.

I don't think you need a PCM. You have an obvious mechanical issue that you are choosing to ignore.

BTW a good scope is going to cost $$$

Looks like you found your problem, get the correct length pushrods.

Didn't even read that part lol