Timing drop and Knock Retard, 1999 Suburban 5.7

[Fast4.7]

So, I regapped the plugs to .050 but I havent test driven it yet. When the plugs were out I performed a compression check:
1: 140
2: 127
3: 128
4: 128
5: 130
6: 132
7: 125
8: 135

Looks ok to me, although cyl 1 is a good bit higher than the rest and it is right next to where the knock sensor is.

I have a transmission question. Does the 460LE use vacuum/MAP to determine when it shifts? I noticed that if the truck downshifts the knock/shudder goes away. I was wondering if it is simply a problem of the truck not downshifting soon enough.

I am curious as to your conclusion #1 is close to the knock sensor. The knock sensor is in the block drain on the passenger side, just in front of the starter and sits between cylinder 4 and cylinder 6 right above the oil pan rail. The only thing I can think of close to cylinder 1 spark plug would be the coolant temperature sending unit for the gauge that is between and above cylinder 1 and cylinder 3 spark plugs.

The transmission shift points and lockup are all controlled by TPS and vehicle speed.

Your compression test seems a little low to me, but my test method may have been different, my gauge is different, etc. What I am looking at is consistency and low cranking pressure in two adjacent cylinders. These engines often blow head gaskets between cylinders 4 and cylinder 6 and sometimes between cylinder 3 and cylinder 5 in a way that they will not leak or burn coolant, just run poorly. Does not appear to be an issue with yours though.

[ccline746pk]

I am curious as to your conclusion #1 is close to the knock sensor. The knock sensor is in the block drain on the passenger side, just in front of the starter and sits between cylinder 4 and cylinder 6 right above the oil pan rail. The only thing I can think of close to cylinder 1 spark plug would be the coolant temperature sending unit for the gauge that is between and above cylinder 1 and cylinder 3 spark plugs.

The transmission shift points and lockup are all controlled by TPS and vehicle speed.

Your compression test seems a little low to me, but my test method may have been different, my gauge is different, etc. What I am looking at is consistency and low cranking pressure in two adjacent cylinders. These engines often blow head gaskets between cylinders 4 and cylinder 6 and sometimes between cylinder 3 and cylinder 5 in a way that they will not leak or burn coolant, just run poorly. Does not appear to be an issue with yours though.

I made an assumption that what I was looking at was the knock sensor. Good to know.

Good to know about the trans, so it should shift properly regardless of the MAP.

I will post again when I have a data log from a test drive.

[ccline746pk]

Drove it today, felt better but I havent driven up my "test hill" so I didnt detect any shudder. The log does still show knock retard engaging during a heavy acceleration event. See log file attached.Burban 8-24-18.hpl

[Fast4.7]

Drove it today, felt better but I havent driven up my "test hill" so I didnt detect any shudder. The log does still show knock retard engaging during a heavy acceleration event. See log file attached.Burban 8-24-18.hpl

I do not understand the knock retard issue you are seeing. Given what I run on these engines and almost never see knock I am begining to wonder if it is not just false knock. Have you tried pulling a couple of degrees of timing in the area it shows knock retard yet? If it still pulls the same amount of timing I would say it is false knock.

My go to spark map on these engines with stock heads and stock or mild cams at 90+ KPA has 12* @ 1,000, 24* @ 2,400 and 30* at 4,000. I also found out it works well with aluminum head engines as a starting point as well.



This is the way a tuned stock L31 should run. 1997 Express 1500 conversion van, 5.7/4L60E and 3.42 G80 at the time. It would break the P255/70R15s loose standing on the throttle from a stop.

https://youtu.be/vc1lHlBLdkw

[ccline746pk]

Here is my latest test run. It did shudder going up the hill. If you look at the log starting at 8:40 you will see the multiple knock retard events which coincide with the shudder i felt.

4.7, not sure what to say. I can stomp the pedal from a standstill and it seems fine, accelerates smooth with plenty of power. Its only happening during low rpm, high throttle settings, and relatively high MAP. I did get a recommendation from a friend for a good shop today, I will be paying them a visit this week.

Is there anyone else on the forum who could review my data and throw another idea out? A different perspective cant hurt. Im planning a trip across country with the whole family the beginning of September and id sure hate to miss something important.....

Burban 8-26-18.hpl

[ccline746pk]

So,

I took the truck to a shop today. They hooked their scan tool to it and we went for a short drive. He noted that he saw no misfires which was unusual according to him. He also saw the cam-crank correlation got up to .6 which he claimed was not acceptable. Overall, we did not experience the worst shudder and what we did see he chalked up to the suspension, ie tires. While I dont believe the tires are the cause I was planning to buy a set before my trip anyway. So at this point Im going to stop worrying and take the trip and see what happens. I will be running fuel system cleaner and a few tanks of high octane through it and see what that does.

Thanks for all the help, I will update if anything changes.

Chris

[Fast4.7]

So,

I took the truck to a shop today. They hooked their scan tool to it and we went for a short drive. He noted that he saw no misfires which was unusual according to him. He also saw the cam-crank correlation got up to .6 which he claimed was not acceptable. Overall, we did not experience the worst shudder and what we did see he chalked up to the suspension, ie tires. While I dont believe the tires are the cause I was planning to buy a set before my trip anyway. So at this point Im going to stop worrying and take the trip and see what happens. I will be running fuel system cleaner and a few tanks of high octane through it and see what that does.

Thanks for all the help, I will update if anything changes.

Chris

I seem to remember the acceptable error being +/- 2* on the CMR. I know mine will tend the vary a little as the rpm changes. It does not stay at a constant value due to changes in the backlash of the distributor gear and timing chain at various loads.

I do not know how soon you plan on taking the trip, but if you are comfortable working on a small block, I would take the time to relash the valves as I described. While I doubt it is the problem you are experiencing I have noticed they seem to run smoother with more power when the are reset.

[ccline746pk]

4.7,

Yeah, I thought that the 2 degree tolerance seemed reasonable. I am leaving on this trip in less than two weeks so I will do the valve lash after. Ive adjusted valves before, nothing to it, just time consuming. On my Mopar im running solid lifters so I have to adjust them from time to time.

Thanks again for all the help!

[Mangonesailor]

Your PE shows that you're going to 11.5 AFR. Do you hit that on your wideband? Maybe you should pull back a little on your commanded EQ. Have you tuned your VE table, because your average LTFT are ? -8 to -13 . It's pulling fuel for some reason or another.

I think you may just have too much advance in those cells that knock retard is showing up. Looking at your TPS you don't show a positive change when it happens... you're also going into PE with 23* of timing. Just seems odd to me. Maybe it'll ring a bell for someone else.

[ccline746pk]

Your PE shows that you're going to 11.5 AFR. Do you hit that on your wideband? Maybe you should pull back a little on your commanded EQ. Have you tuned your VE table, because your average LTFT are ? -8 to -13 . It's pulling fuel for some reason or another.

I think you may just have too much advance in those cells that knock retard is showing up. Looking at your TPS you don't show a positive change when it happens... you're also going into PE with 23* of timing. Just seems odd to me. Maybe it'll ring a bell for someone else.

Mango,

During this whole troubleshooting process/thread I adjusted the stock fuel map by 2 percent upon the advice given here. I do not have a wideband yet, I know I badly need one. I have not touched the timing yet, keep in mind this is a bone stock engine/vehicle. I am not opposed to adjusting the timing, but my experience in adjusting timing up until now has been using a timing light and twisting a distributor. The timing tables are intimidating to me and without step by step instructions I am hesitant to go tinkering for fear I would mess it up.

See the following post for the latest developments.

[ccline746pk]

So, today on the way back home with the family on a leisurely drive the Check Engine light popped on. I ran the codes in VCM Scanner and heres what populated:

Burban Codes 9-2-18.PNG

P0300 and P0306, Random Misfire and Cyl #6 Current Misfire. The kicker is Im supposed to be loading the family up driving it 1300 miles this Thursday! So, whats the most common cause for the random misfire code on the 5.7??

[Fast4.7]

So, today on the way back home with the family on a leisurely drive the Check Engine light popped on. I ran the codes in VCM Scanner and heres what populated:

Burban Codes 9-2-18.PNG

P0300 and P0306, Random Misfire and Cyl #6 Current Misfire. The kicker is Im supposed to be loading the family up driving it 1300 miles this Thursday! So, whats the most common cause for the random misfire code on the 5.7??

I figured the shuddering might be a misfire and that could also be the cause of the knock retard.

If the ignition system is good (I still would not bypass the possibility of having new bad parts or a failing coil), knowing you have fairly consistant compression, that leaves fuel. Which means the spider. I worked in an independent shop back in 2005-2006 and they were such a common failure I got to where I could change them out in about 45 minutes on anything except an Express van or Astro/Safari and those took about 1.5 hours because of having to pull and reinstall the engine cover and dealing with the cramped engine compartments. I bet you could order the Delphi MPFI spider on Amazon and have it to your door in time to change it out and still go on your trip. What is weird is I used to see P300 and P305 most commonly on trucks with bad spiders and leaking regulators but honestly any one of the poppets could start sticking or the feed tube to the poppet could break.

[Fast4.7]

Mango,

During this whole troubleshooting process/thread I adjusted the stock fuel map by 2 percent upon the advice given here. I do not have a wideband yet, I know I badly need one. I have not touched the timing yet, keep in mind this is a bone stock engine/vehicle. I am not opposed to adjusting the timing, but my experience in adjusting timing up until now has been using a timing light and twisting a distributor. The timing tables are intimidating to me and without step by step instructions I am hesitant to go tinkering for fear I would mess it up.

See the following post for the latest developments.

It is a little rich now but better rich than lean.

If you choose to do the spider, I would also pull the lower intake, soak the thing in oven cleaner and get a wire brush after it. The carbon buildup from the EGR system will be horrendous. I know this is not wjat you wanted to hear but it could definately save you alot of time and money. I lost a 57K mile 1997 350 after it snapped #2 rod on startup from hydraulic lock back in 2004 from a failed intake gasket requiring a new crate engine to replace the windowed block.

[ccline746pk]

4.7,

Thanks for the reply. I checked the #6 plug wire then cleared the codes and drove it today. Data log attached. Knock retard events happens starting at 2:49. I have been thinking about the fuel spider because I know they are problematic on these models. But, I hate to swap more parts without knowing it's causing the issue for sure. That said, since I know everything else is good im thinking it should be ok to go ahead and head out on the trip. I did do a leak down check and it held pressure fine, 55psi for over 5 minutes. I will run a tank of Chevron Techron fuel through it and hopefully it will free up the poppets if they are sticking.

I am going to get a wideband asap. Its frustrating not knowing what the AFR is out the tailpipe. Thanks for all the help again. Wish me luck!

Burban 9-3-18 return.hpl

[Mangonesailor]

Any update on all of this?

[BoominSVX]

I know I'm late, but just wanted to throw something out there. I had similar issues a few years back with my caddy. Same thing as that burban. Had some 0300 codes and a few other misfire codes after months stuttering and rough idle. Finally got bored with some friends and a beer and decided I wanted to pull my egr off and clean it. Well I'll be darned if the thing wasn't stuck open. I cleaned it, plugged it back in, commanded the egr to 100% a few times with my scan tool and unplugged it so the pintle would slam shut (just cause beer), and the third time, slam. Instant smoothe. Instant misfire fix. Instant random driveway happy dance.

That being said, Fast4.7 seems very knowledgable on the L31. I have a 99 escalade over here with the 395 cam, cold air, shorty headers and soon will have no cats. Shift kit and corvette servo as well. It's running the factory black box. Do you happen to have one that I could reference for a base to work off? Seems to be a pretty common setup. I put the cam in during a complete rebuild about 2 years ago. Just getting around to tuning it. Probably cut her life span in half but... priorities, ya know?