1999 Vortec 454 Build - struggling with tune

[Philip Parker]

Hi everyone. I'm a seasoned tech but have no experience with EFI tuning. I recently rebuilt the top end of my personal pickup's 454 (L29) and had a mail order tune done but something is off.

Engine has replacement Brodix heads and a cam. Intake, Injectors and ECM are all stock (black box). Bottom end is stock. From what I can tell the engine is running very lean and it is pulling tons of timing in certain kpa regions. Any input would be highly appreciated.

Tune and two logs are attached.

Thanks in advance!

Philip

[kevin87turbot]

It's not a fuel problem, it's a timing problem. It doesn't have near enough timing for that engine. It was down in the 9-12 degree range at WOT on your datalogs. GM recommends 26 degrees max on their crate engines, but I typically start with 28 degrees on the L29 applications and see how they perform. I've had some that did best at 30-31 degrees...or on carbureted applications, around 32-33 degrees. You'll have to be careful with the rpm on yours...you'll run out of injector pretty quickly on those. Try the attached file and see how it performs.

Big Blue Tune KW Mod.hpt

[Philip Parker]

It's not a fuel problem, it's a timing problem. It doesn't have near enough timing for that engine. It was down in the 9-12 degree range at WOT on your datalogs. GM recommends 26 degrees max on their crate engines, but I typically start with 28 degrees on the L29 applications and see how they perform. I've had some that did best at 30-31 degrees...or on carbureted applications, around 32-33 degrees. You'll have to be careful with the rpm on yours...you'll run out of injector pretty quickly on those. Try the attached file and see how it performs.

Big Blue Tune KW Mod.hpt

That's where I am confused. It only really does it in closed loop and my timing starts at 26 at idle. Once I get into the throttle it starts dropping timing like crazy and I (assume) it is because of a lean condition so it is trying to avoid detonation.

Why is the ECM dropping timing as I increase revs?

[Philip Parker]

I found the timing tables and it is doing just what is listed in those tables. Are the heads just moving that much more air at 1200 rpm that I need to adjust the timing tables? If I just cruising around town at 25 mph I will see like 75 kpa with maybe 10% tps.

[kevin87turbot]

The problem is simply in the tune.
Once you load the tune that I posted above, then you can give me a datalog. At that point, we can determine if the fuel trims need to be adjusted.

[Philip Parker]

I loaded your tune and it is dramatically better thank you. Truck is starting to pull more normally. I am starting to get the hang of what to look for and what I'm noticing is that the biggest drivability issue is in the 1200 rpm column between 60-75 kpa. Truck feels like it is almost misfiring at that point. Very Sluggish where the timing starts to drop off there. I've attached the latest log file.

[kevin87turbot]

I loaded your tune and it is dramatically better thank you. Truck is starting to pull more normally. I am starting to get the hang of what to look for and what I'm noticing is that the biggest drivability issue is in the 1200 rpm column between 60-75 kpa. Truck feels like it is almost misfiring at that point. Very Sluggish where the timing starts to drop off there. I've attached the latest log file.

That looks much better. Probably needs a little more timing down low. Try this revision.

Big Blue Tune KW Mod 2.hpt

[Philip Parker]

I loaded this tune and attached the log. Doing a crank relearn I did get a couple backfires around 3500 and above with significant throttle input. Gradual throttle kept the backfires at bay. Did not notice any during a loaded WOT run. Looking at the spark table of Mod 2 I am not measuring the same advance in the scanner that the table is calling for.

I'm still getting stumble at 60-75 kpa in the 1200 column. As soon as it migrates to the 1600 column and I'm running closer to 29 degrees is goes away.

What is the wisdom behind pulling the timing as kpa goes up for each column? Is that detonation land? Would an increase in advance from 50-70kpa in 1200 column be risky? With gearing and everything else the truck spends lots of time in that column between 40-70 kpa.

[Philip Parker]

oops here is the log

[kevin87turbot]

As load increases, so does cylinder pressure. At that point, timing needs to decrease.
The actual timing may not exactly follow this main timing tables. There are several timing modifier tables that will affect the timing as well.

The backfire that you're experiencing is odd. I didn't see any reason for that to occur. I wonder if there's a problem with one of the plugs/wires distributor cap?

I don't see the datalog from that last tune.

[Philip Parker]

The summit distributor will not zero out with cam retard measurement given it's shape and clearance to the intake. Advancing or retarding teeth will only make it worse, it's like the keyed table that the rotor sits in is off. One guy over at GMT400.com has experienced this as well. When I rebuilt I did everything except the short block, and so far I am unable to get a confirmed crank relearn.

I attempted it with VCM scanner this morning, I'm about to look at the cam retard on my scanner and see if it's any closer.

I forgot to include the scan in my last post but added to post #9.

[Philip Parker]

Closest cam retard I can get is -5, so I am 5 degrees retarded from 0 basically. Crank relearn seems to not have done anything.

The cam does have"4 degrees" of advance ground into it from crower but I doubt the reluctor or sensor marker for the cam sensor was changed. That would be odd.

Idle is a bit lumpy for such a mild cam, but I chose 113 LSA for vacuum. I'll do another log as well.

[Philip Parker]

Here is the latest log. Still got that weird bog at 70kpa and 1200. Does is need a touch more fuel? My first impression is that it feels like it a bad burn in those sectors.

My first steps after noticing the driving condition were to do plug and wires. Have a full 8mm set with NGK copper cores.

[kevin87turbot]

It looks good as far as the fuel trims at that rpm.

[blindsquirrel]

Closest cam retard I can get is -5, so I am 5 degrees retarded from 0 basically. Crank relearn seems to not have done anything.

Pull the distributor. Knock out the roll pin and turn the distributor gear 180* on the shaft, re-pin. The distributor gear has an odd number of teeth, so reclocking like this will shift your range of adjustment.

[Philip Parker]

Pull the distributor. Knock out the roll pin and turn the distributor gear 180* on the shaft, re-pin. The distributor gear has an odd number of teeth, so reclocking like this will shift your range of adjustment.

Roger that. Gracias.

[Philip Parker]

Yeah the O2mv corroborates that. I'll get the 5 degrees out of the dizzy and see what happens. Many thanks for your help and the tune mods.

[Philip Parker]

It looks good as far as the fuel trims at that rpm.

This may or may not be a clue, but the weird misfire and dipping into the 70kpa region only happens when the engine is warmed up and in closed loop. I did a log this morning of a cold start and drove it up a couple hills - exactly the same conditions when I get the misfire - and the load isn't getting anywhere near 70 kpa. No misfires. Everything is good - that is the first scan,

I saved that log then started recording as the engine warms up and after about three stop signs it starts to dip into 65-75 kps region and there is the misfire.

I am starting to wonder if I have a parasitic load from the transmission or torque converter that happens when it gets hot. Like there is poor torque transfer happening after the fluid warms up a bit which is necessitating more throttle input and consequently more load and the 70 kpa/1200 zone. I don't get anywhere near that zone with a cold engine and trans.

[Philip Parker]

I have more info on this as I have been diagnosing for the past week.

What I am experiencing is a dramatic decrease in intake vacuum without much throttle input. The ecu is seeing the high kpa reading and assuming that I have a significant load happening when I don't. I'm on flat ground with an empty truck. It retards timing as per the table, and I suppose is ignoring the TPS. This is corroborated by the fact that hills make the situation worse (more load).

So basically I have a vacuum leak somewhere that gets worse when I reduce vacuum by opening the throttle a bit. What would do that? The heads and cam are not wild at all and my fuel trims seem normal. Replaced the MAP today - no change. Unplugged the MAP and the problem goes away.

[doorev800]

I would get yourself a wide band and log afr error. Also add knock retard and Power Enrichment to your parameters. Verify your fuel first then go and fine tune the timing. Scan #6 has your narrows reading .883v at wide open in one area of the log which is on the lean side, normally a good rule of thumb is being above .900v min for wide open in power enrich. This is of course just a educated guess, that is why you need a wide band to verify.