Timing drop and Knock Retard, 1999 Suburban 5.7

[ccline746pk]

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.

4.7,
So I get the timing now, I understand the HVAC will make it spkie down and I did look back and the long events where it was at -10 were when the tps was zero. I am so green right now, up to this point my mechanical abilities have been limited to carburetors so im just trying to understand how the system is supposed to work. So in your first post you say "The second screen shot is from the engine running too lean." I understand I need to change the overall AFR to 14.1:1. I am sure I know where to do that.

Second, I will clean the MAF.

Third, I will double check the fuel pressure but I think it should be fine as I replaced the pump and filter in the past year.

Fourth, can you explain your statement, "fuel trims should be much more neutral." When it comes to the charts right now they are greek to me. Is there a good tutorial you can point me to? For the fuel trims, LT, ST etc. And for the spark table as well for that matter. I can use a timing light and twist a distributor like nobody business but Im struggling here.....

Thanks again,
Chris

[ccline746pk]

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.

I have not checked the "cam crank correlation, I will put that on the to do list.

[Fast4.7]

I have not checked the "cam crank correlation, I will put that on the to do list.

Since you have not performed that procedure after the distributor replacement that is the first place I would start.

[Fast4.7]

4.7,
So I get the timing now, I understand the HVAC will make it spkie down and I did look back and the long events where it was at -10 were when the tps was zero. I am so green right now, up to this point my mechanical abilities have been limited to carburetors so im just trying to understand how the system is supposed to work. So in your first post you say "The second screen shot is from the engine running too lean." I understand I need to change the overall AFR to 14.1:1. I am sure I know where to do that.

Second, I will clean the MAF.

Third, I will double check the fuel pressure but I think it should be fine as I replaced the pump and filter in the past year.

Fourth, can you explain your statement, "fuel trims should be much more neutral." When it comes to the charts right now they are greek to me. Is there a good tutorial you can point me to? For the fuel trims, LT, ST etc. And for the spark table as well for that matter. I can use a timing light and twist a distributor like nobody business but Im struggling here.....

Thanks again,
Chris

LTFT is Long Term Fuel Trim and it is more of a picture of what is happening over a long period of time where Short Term Fuel Trim is more instant. In fact changes in STFT are what move the LTFT values stored in the PCM. When I say Neutral I mean values close to Zero which means the fuel trims are not being used to alter the fuel delivery. Positive numbers are lean and negative numbers are rich.

I would set your commanded air/fuel ratio to 14.1 in the fuel tab, clean the MAF, set the distrivutor then relog and see where you are.

When I tune these I tend to try to keep my fuel trims in the -5% to 0% range. Keep the tune slightly rich and let the 02 sensors pull a slight amount of fuel as necessary. It helps with throttle response and engine smoothness.

Finally at your mileage I would consider a running valve lash adjustment. I have found these engines all over the place as far as rocker adjustment. Either the factory did a horrible job or the adjusment nuts move over time. I have found these engines seem to run best and have nice torque gains if you go with zero lash plus 1/4 turn. I do the passenger side first starting with a cold engine since you have to remove the belt and loosen the compressor bracket to gain acess. With a cool engine you can run the engine a short period of time without getting it too hot from lack of coolant circulation. Then you can shut it off, put it back together and then gain acess to the passenger side and with the engine now able to have a belt and cooling system functioning do the passenger side adjustment. I did a running adjustment and 1/4 turn lash on a 120K mile engine and I was amazed how much stronger and smoother it ran and how seamlessly it reved on acceleration.

[cobaltssoverbooster]

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.

been there before...i understand

[Jay@HAP]

I have not checked the "cam crank correlation, I will put that on the to do list.

You want it as close to zero as you can get, you have to raise the RPM's to 1300 or so to check it correctly.

[ccline746pk]

LTFT is Long Term Fuel Trim and it is more of a picture of what is happening over a long period of time where Short Term Fuel Trim is more instant. In fact changes in STFT are what move the LTFT values stored in the PCM. When I say Neutral I mean values close to Zero which means the fuel trims are not being used to alter the fuel delivery. Positive numbers are lean and negative numbers are rich.

I would set your commanded air/fuel ratio to 14.1 in the fuel tab, clean the MAF, set the distrivutor then relog and see where you are.

When I tune these I tend to try to keep my fuel trims in the -5% to 0% range. Keep the tune slightly rich and let the 02 sensors pull a slight amount of fuel as necessary. It helps with throttle response and engine smoothness.

Finally at your mileage I would consider a running valve lash adjustment. I have found these engines all over the place as far as rocker adjustment. Either the factory did a horrible job or the adjusment nuts move over time. I have found these engines seem to run best and have nice torque gains if you go with zero lash plus 1/4 turn. I do the passenger side first starting with a cold engine since you have to remove the belt and loosen the compressor bracket to gain acess. With a cool engine you can run the engine a short period of time without getting it too hot from lack of coolant circulation. Then you can shut it off, put it back together and then gain acess to the passenger side and with the engine now able to have a belt and cooling system functioning do the passenger side adjustment. I did a running adjustment and 1/4 turn lash on a 120K mile engine and I was amazed how much stronger and smoother it ran and how seamlessly it reved on acceleration.

4.7,

I will be cleaning the MAF, setting the AFR to 14.1 and checking/adjusting the distributor and will relog and repost. Hope to do all that this evening. Thanks again! I will keep everyone posted.

Chris

[Fast4.7]

4.7,

I will be cleaning the MAF, setting the AFR to 14.1 and checking/adjusting the distributor and will relog and repost. Hope to do all that this evening. Thanks again! I will keep everyone posted.

Chris

Keep us posted on what happens.

Chris

[ccline746pk]

Alright,

Checked Fuel Press: 52-55psi at port near throttle body.

Crank-Cam correlation (distributor timing) was 7.4 degrees, adjusted to -0.3

MAF, looked clean but cleaned it anyway with CRC MAF cleaner

Reloaded stock tune (just to be sure) with only adjustment being AFR at 14.1:1.

Attached is the test run. Didnt shudder/stutter or indicate any noticeable problem (but it doesnt always do it anyway) but it is still going into KR and if im reading the fuel chart right it is going lean. I understand there is a Fuel Injector Balance tool in the VCM scanner. Would it be beneficial to use it for trouble shooting, and if so where is it? I cant seem to find it

Burban after stock tune+14.1 afr, maf clean, cam-crank set.hpl

[Fast4.7]

Fuel pressure seems low to me if the gauge is accurate. Stock spiders run about 62 psi Key On Engine Not Running and about 56 psi at idle. MFI spider was 58 psi Key On Engine Off and 52 PSI at idle.

Post a screen shot of your LTFT table from the datalogger.

[Fast4.7]

I have smoke tested these intake manifolds before and found vacuum leaks in intake gaskets that seemed to be good otherwise.

[Fast4.7]

I would look at your datalog tonight but my tuning laptop is at my shop across town.

[ccline746pk]

Capture.PNGSTFT.PNG

Here are two screenshots, one of the LT Fuel Trim and another of the ST Fuel Trim, both of the exact same time grab. This is also a knock retard event. And two more below where I scrolled up the channels.

STFT.PNGLTFT.PNG

[Fast4.7]

Your fuel trims look MUCH better from first glance, compared to LTFT of +10% prior. Still slightly lean in places but nothing drastic. Here is what I would try next. First open both of your VE tables and add 2% to both the Primary and Backup VE tables. Then add 2% to the whole MAF table. To do that simply select the whole table and multiply by 1.02. Repeat for all 3 tables. Then look at your PE tab. Set the entry rate as high as possible, generally this caps at the 2.00 to 4.00 range. Set the RPM to bypass PE delay to something just above idle, I typically use 800 rpm. Set the PE time delay to zero if applicable. Then adjust both Cold and Hot TPS thresholds to around 50%. Lets see if getting your engine the fuel it wants when it wants it when you put a heavy load on it eliminates that knock retard. From my experience with the PE settings like that you will be able to feel when PE kicks in on acceleration. The engine will just seem to kick in and pull hard as soon as you hit that TPS threshold.

[ccline746pk]

I have smoke tested these intake manifolds before and found vacuum leaks in intake gaskets that seemed to be good otherwise.

I did do intake leak test not long ago where I sprayed starting fluid around the intake area, the rpm never changed so I think Ive eliminated that as a possibility. I could do a smoke check, but i would have to buy or make a smoke tool.

[ccline746pk]

Your fuel trims look MUCH better from first glance, compared to LTFT of +10% prior. Still slightly lean in places but nothing drastic. Here is what I would try next. First open both of your VE tables and add 2% to both the Primary and Backup VE tables. Then add 2% to the whole MAF table. To do that simply select the whole table and multiply by 1.02. Repeat for all 3 tables. Then look at your PE tab. Set the entry rate as high as possible, generally this caps at the 2.00 to 4.00 range. Set the RPM to bypass PE delay to something just above idle, I typically use 800 rpm. Set the PE time delay to zero if applicable. Then adjust both Cold and Hot TPS thresholds to around 50%. Lets see if getting your engine the fuel it wants when it wants it when you put a heavy load on it eliminates that knock retard. From my experience with the PE settings like that you will be able to feel when PE kicks in on acceleration. The engine will just seem to kick in and pull hard as soon as you hit that TPS threshold.

Not to second guess you but before I dive into tuning do you think my log looks good otherwise? (I can get a longer log file to see if it will shudder) In other words, would you suspect any other part malfunction at this point or from what you see or it is likely just a tuning issue? Could the issue be coming from the MAF, O2 Sensor(s), or fuel tank purge valve, and if so do you know of good ways to eliminate these possibilities? I ask because I understand those items can cause issues on these engines as well.

Thanks,
Chris

[Fast4.7]

Not to second guess you but before I dive into tuning do you think my log looks good otherwise? (I can get a longer log file to see if it will shudder) In other words, would you suspect any other part malfunction at this point or from what you see or it is likely just a tuning issue? Could the issue be coming from the MAF, O2 Sensor(s), or fuel tank purge valve, and if so do you know of good ways to eliminate these possibilities? I ask because I understand those items can cause issues on these engines as well.

Thanks,
Chris

I have not looked over your datalog. I was merely looking at your LTFT table as well as what the sensor readings looked like in the snap shot.

You could have another malfunction that will show up on a longer run but it is difficult to say. If your MAF was bad or you had a bad 02 sensor your fueling would be all over the place. As for the purge valve, if it failed in the open position you might possibly see rich fuel trims around idle but really nothing else since it purges continuously once the engine is up to operating temperature and above idle.

On a stock engine I would expect the MAF to read in the 180-220 gm/sec range at heavy throttle in the 3,500-5,000 rpm range and about 8-10 gm/sec at warm idle. That would be around 23.8-29.10 lbs/min at heavy throttle, mid to high rpm and 1.05 to 1.32 lb/min at idle.

[ccline746pk]

OK, I will check the MAF readings when I take it out for longer data log test drive, hopefully tonight. And I will go ahead and change the VE, MAF, and PE tables/settings.

I do want to improve the trucks tune, thats the biggest reason I bought the software, but I just want to make sure im not missing something thats broke. Ive had this truck for the past 3yrs or so and ive put 25K miles on it and this issue popped up recently, but again only during certain load conditions. It very well may be something thats been developing for a while, I just might not have noticed it before now.

Thanks for all the advice, I will keep the forum posted.

Chris

[Fast4.7]

OK, I will check the MAF readings when I take it out for longer data log test drive, hopefully tonight. And I will go ahead and change the VE, MAF, and PE tables/settings.

I do want to improve the trucks tune, thats the biggest reason I bought the software, but I just want to make sure im not missing something thats broke. Ive had this truck for the past 3yrs or so and ive put 25K miles on it and this issue popped up recently, but again only during certain load conditions. It very well may be something thats been developing for a while, I just might not have noticed it before now.

Thanks for all the advice, I will keep the forum posted.

Chris

I think you will like the difference from the minimal changes I am suggesting with the fuel map and PE settings.

If there is something else popping up it very well could be something electrical or mechanical starting to fail.

If you suspect 02 sensors they are relatively cheap to buy as AC Delco service parts from Rockauto or Amazon. Mine even came out relatively easily on the Express van and the Tahoe. I consider the front 02 sensors a maintenance item at around 100K miles myself.

A longer drive never will hurt. It gives electronic parts a good amount of time to heat soak and most electronic failures will happen at that point.

[ccline746pk]

So, im going through the tune and ive found and adjusted most of what you recommended, but I have a few questions. When i added 2% to the MAF Airflow vs. Freq chart it gave me this warning:

Param Exceed.PNG

I went ahead and made the change but is it ok?

Second, under the PE tab, where or what is the "entry rate", is that the "Enrichment Rate"? If so it turns red if I go as high as 1.00. Is that ok?

Lastly, where is the "hot and cold TPS threshhold" setting?

Thanks for your patience,
Chris