Timing drop and Knock Retard, 1999 Suburban 5.7

[ccline746pk]

First, Im a newbie, not sure if im posting this in the right area of the forum.

Ive got a Chevy Suburban, 5.7 with 157K miles that im just starting to tune. But, ive got an issue at the moment that I cant seem to fix. It has a shudder/stutter that shows up when under load, high throttle settings. It goes away if I back off the throttle, or it downshifts. Ive run VCM scanner, attached is the latest data log file. Ive replaced numerous sensors and the usual tune up items in misguided/lazy attempts at troubleshooting. The data consistently shows two things that I dont understand. First, the timing drops erratically, sometimes from 30 degrees advance down to -10 degrees. Second, it goes into Knock Retard mode which is, I believe, why it is shuddering under load. I just dont know whats causing it to go into knock retard. I have not replaced the knock sensor(s) yet as I dont know if they are bad. Of course that hasnt stopped me previously.... Also attached are two screen shot, one of the timing drop and the other of the knock retard event.

99 Suburban Timing Anomoly.PNG99 Suburban Knock Retard Anomoly.PNGBurban scan after Brake booster.hpl

[cobaltssoverbooster]

attach tune file


i dont see a wideband channel. i see a commanded afr channel that doesnt change. the oem sensors cant be used for tuning pe ranges. it is likely the fueling up on the top end is way off.
still need a tune to verify a few other things aren't interfering when they shouldn't be

[ccline746pk]

Cobalt,

As im new im not quite following your request. When you say "attach a tune file" what do you mean, or where do I find that? Im sure this is very basic, sorry. Thanks for the post, I can use all the help I can get.

Chris


Is this what you're looking for?

Burban Baseline 8_12_18.hpt

[orange ss]

replace distributor cap

[cobaltssoverbooster]

yeah thats what i was requesting. have to look at it when i return to the shop later today.

Cobalt,

As im new im not quite following your request. When you say "attach a tune file" what do you mean, or where do I find that? Im sure this is very basic, sorry. Thanks for the post, I can use all the help I can get.

Chris


Is this what you're looking for?

Burban Baseline 8_12_18.hpt

[ccline746pk]

Cobalt, thanks!

Orange SS,

Ive replaced:

Cap
Rotor
Distributor (Accel aftermarket) with pickup sensor
Plugs and wires
Crank Sensor
TPS sensor

and a brake booster and master cylinder, but I digress.

The problem has not changed, it existed before all these parts were swapped and it remains. The truck still runs great, with the exception of the aforementioned occasional knock retard episodes under heavy load.

Thanks for the help guys!
Chris

[cobaltssoverbooster]

ok so first thing i notice is the pe settings need refining.
to determine the value to enter into your pe ratio table take your stoich value 14.7 and divide it by your target afr.
so for na application requesting 12.3 you would get a value of 1.195.

once you set these target values you dont change them. instead to correct the fueling you tune either the VE in Speed Density mode or the MAF in Maf mode.

COT (catalyst over temp) can cause rich modes because it calculates cat temp based on commanded values. i suggest turning this off until things are sorted out and if you feel you need that feature then turn it back on after tuning and accept that performance may change when COT mode triggers.

set your spark retard vs. torque reduction table under torque management to '0'. if tqm does trigger then it will pull ignition and this prevents that from happening.
disable drivetrain abuse mode by setting the value to 0 mph. if you mash first gear then it will trigger abuse mode and try to use the spark cut tqm table.


try logging these items to help us out a bit more:
rpm
coolant *f
advance *
knock *
iat *f
maf hz
map kpa
commanded afr or equivalence ratio
injector pulse ms
injector duty %
stft b1
ltft b1
stft b2
ltft b2

i highly suggest you get a wideband installed and logging in the scanner software. you can tune the entire fuel map off the wideband by disabling the trim system and when your done you just re-enable it for daily driving and call it good. the wideband is the only way you can tune the WOT range of the ecu.
since you replaced all physical components related to this im going to assume the physical side of the system is good to go. this means you either have a large fueling error causing issues with detonation or you have a tqm event removing ignition as a safety precaution.

[orange ss]

Did you perform CASE relearn after swapping crank sensor?

[Fast4.7]

set your spark retard vs. torque reduction table under torque management to '0'. if tqm does trigger then it will pull ignition and this prevents that from happening.
disable drivetrain abuse mode by setting the value to 0 mph. if you mash first gear then it will trigger abuse mode and try to use the spark cut tqm table.

I would HIGHLY RECOMEEND NOT DOING THAT if you want to keep your weak 4L60E in one piece! My tuned but otherwise stock 350 Vortec broke hard parts in a 4L60E in 38K miles and with a mild cam broke a built up 4L65E in 40K miles. From that experience I warned a buddy about doing the same but he begged and begged me to disable the TQ management in his 0411 swapped 1997 C1500 with a built 4L65E. His stock 350 with shorty headers, exhaust, electric fans and a cold air broke his "BUILT" trans in 15K miles.

[cobaltssoverbooster]

its to diagnose where the pull is coming from.

[Fast4.7]

its to diagnose where the pull is coming from.

I can tell you without a doubt the first screen shot is Decel fuel cut-off and timing retard is completely normal there. The second screen shot is from the engine running too lean. If the fuel is E10 aka 10% ethanol the commanded air fuel ratio needs to be changed from 14.7:1 to 14.1:1. I would also get a can of CRC MAF cleaner and spray the maf filiments. If the fuel pressure is normal and the truck is stock at that point the fuel trims should be much more neutral. Then set the high MAF failure code to error on first occurance and set the MAF high failure frequency to Zero. Tune the VE tables in speed density mode. Then turn the MAF on amd set the exit RPM for dynamic air calculation to a very low rpm and tune the MAF table. Once the fueling is right then concentrate on the spark map.

[Fast4.7]

Also once the fueling is correct I would drop the PE enable threshold down to something more reasonable. I usually go down to about 40% TPS on a Vortec 305 or 350 when I tune them. There is absolutely no reason to be standing on the pedal more than 1/2 way with a high MAP reading indicating heavy engine loading and not having any additional fuel enrichment.

[Fast4.7]

Finally knock retard showing has nothing to do with abuse mode or torque management. Both of those show up as a SA reduction compared to the timing map on the Vortec PCMs. Even vurst knock retard settings show up as SA reduction not as knock. If knock is showing up it is being triggered by the knock sensor. Either real knock or noise.

[Fast4.7]

I will also add that my Express van L31 when it still had a distributor and single coil started shuddering under load and misfiring. Kept getting progressively worse. We had cold wet weather followed by an overnight freeze. The next day it would not start. I pulled the doghouse cover and quickly doscovered it did not have spark. The coil itself a crack in it and was arcing itself out internally to the metal coil bracket. Changed the coil with a used spare I had laying around and it fired right up. I had ALOT more power all around and the misfiring disappeared. That coil had less than 100K on it at the time. Good luck finding your issue.

[cobaltssoverbooster]

ill just let you take this over. you seem to know the quirks and im just going about my general methods of searching for triggers.
i do believe fueling is a big issue on this though and i believe you agree on that

[Fast4.7]

I am sorry for acting like a know it all. I have owned about 6 of these now. I have swapped 3 of them to 0411s. I have also tuned about 20 of them from stock to heads/cammed/intake and even a supercharged one. I have gotten to where alot of the time I can look at a log and know what is happening.

[ccline746pk]

Thanks to both of you. I will try to digest and implement your advice. I'm leaning towards it being a fuel issue but need to pinpoint something before I start swapping parts again.

Fast4.7, have you had one of these give you trouble related to the fuel spider? I've read they can get sticky/clogged poppets.

[ccline746pk]

And another question for you 4.7, you said the timing where it dropped to -10btc is normal? I've seen it do that in other places too, even steady state throttle where it just spikes down and back up, is that normal as well?

[Fast4.7]

And another question for you 4.7, you said the timing where it dropped to -10btc is normal? I've seen it do that in other places too, even steady state throttle where it just spikes down and back up, is that normal as well?

Is it less than about 5% TPS when you see the downward spikes? If you are at low TPS it could still be deceleration fuel cutoff because. Also is the HVAC system on when you see the spike downward? Often these are setup for a/c bump torque which helps keep the torque output steady when the a/c compressor cycles. Finally torque management related to the transmission will happen either from a WOT stab from a stop or during shifting. You won't have torque management in play cruisibg along in the same gear.

Also have you checked the cam crank correlation. You can enable it in the datalog and adjust the distributor as near Zero as possible. The reading is most accurate during a moderate throttle snap above 1,200 rpm. I watch the scanner while I blip the throttle and observe the reading while the engine is accelerating. For the record the spider in my Express was changed to the MFI spider in 2006 with only 57K on it but it sat with a blown up engine for nearly a year. My brothers 1999 Suburban had the stock spider at 120K. My 1999 Tahoe has the stock spider at 140K. My brothers 4.3 S10 made it to 220K with the stock spider. My aunts 1997 Tahoe only made it to about 90K before it was replaced. There is really no way to put a failure mileage and timeline on them.

[Fast4.7]

Also one tine my Tahoe started having a noticeable misfire and a shudder at cruising speeds under load that became so bad that it would not go into 4th gear or lock the torque converter. The distributor clamp had loosened and my CMR was at -22?. Reset it back to Zero and the thing was back to running great. It never set a P1345 either.