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Cutting out under WOT, in boost areas.

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Hello all, have a issue with my truck and hoping to get some answers possibly from you guys! I have always found the answers I need in this forum when I haven't been able to figure it out so I hope you guys can help me figure out this one.

87 S10

2001 LR4 4.8l V8

4l60e auto trans

PAC 1218 Valve Springs

MLS headgaskets

Trunnion upgrade Kit

Isky Triple 12 cam (212/212 110 LSA)

Deatschwerks 60lb/hr Injectors

Walboro single 450lph fuel pump

Hp tuners

TR6 plugs gapped to 0.020 (brand new)

New spark plug wires

New Coil Packs

Stock truck throttle body and intake manifold

GT45 front mount turbo

A2A intercooler

48mm Wastegate

50mm BOV

I think that's all the pertinent stuff (If I forgot anything, just ask)

SO.. I have a problem going to WOT on my current setup. I can go to WOT physically, and it reads at/or near 100% when foot is all the way down. My problem is around 4400-5200 RPM where it seems to cut out. Feels almost like I'm hitting the rev limiter but I know thats not the case. It sounds like right when the Waste gate begins to barely open but not all the way open, if that makes sense. I have what should be a 7lb spring in the gate. now, this setup worked before in its current configuration, but only for a few pulls then it started acting up. I have noticed the MAP begins to drop significantly in this area when the problem occurs, almost as if I let off the throttle, but I'm still WOT. When I let off the throttle, I can hear the BOV doing its job, releasing the excess pressure. Like I said though, it feels like I'm hitting a limiter of some sort or like it just doesnt want to go, the truck still pulls, not like it completely dies, but when I let off, I can almost immediately get back into it but in the same exact area as before around 120 to 125kpa, and 4400 to 5200 RPM it cuts out. When this first started, I suspected Spark blowout, so NEW TR6 plugs, which I believe are 2 ranges colder than factory plug, gapped to 0.025 worked for a few pulls, then down to 0.020 when problem persisted. replaced plug wires and coil packs as an act of desperation, and have tried many different changes to the timing and fueling up and down to no avail. I have done my best to check for boost/vacuum leaks with no obvious problems found. Im beginning to think that's its got to be something in my tune.

After all the troubles I've been having I set everything back to the way it was when it was originally working and did a log cruising around and a few wot runs. hoping someone here can check out my tune and my logs and might be able to point me in the right direction. Cruising is great, and there is no presence of knock activity when this problem occurs and my factory knocks sensors are working, I can tap on the valley pan while its running and it registers in the scanner.

Sorry for the long post, wanted to convey as much as I could so there isn't a lot of back and forth questions.



Attached Files

Alrighty guys!!! Went for a drive with the same exact tune that's posted, after work. Made a few pulls, and as soon as I get home and get the laptop on the charger I'll post up my logs. Got a decent cruise file and quite a few WOT runs in. The very first WOT pull I was shocked!! It worked!!!! Everything was as it should be. Now, not being one to leave well enough alone, I kept doing WOT pulls. Something didnt make sense. So kept on choo-chooing down the road and on the very last pull... it did it again!!! Post up logs and some more info when I get home. Feel like with everything I'll throw at you guys, the problem will rear its ugly head.

Okay, so continues the saga of my little S-10 build:

As previously stated, I decided to try out a couple runs with the truck this evening after work, and had some interesting results.

I logged a total of 5 WOT pulls, and on the 6th and final pull, it acted out again. One thing i did notice is that when I went to work today, the ambient air temp was 88 degrees. After work this evening it was about 67 degrees. Small temperature change, but I have a sneaky suspicion someone may chime in and mention that. I'm almost wondering if maybe even though I have a colder range spark plug than stock, that I shouldn't go one step colder. I've heard a lot of people like to use the NGK BR7EF / 3346 for Turbo LS V8's. I know that the heat of the plug can have an affect on cylinder temps so that why I'm curious if that isn't it. I'm not going to post up ALL the log files , because I feel that I've already bombarded you all so much with data. I'm posting the two exceptional runs (22 and 44) a steady state cruise log where I did end up seeing a little knock highest being .9 degrees in one spot, the other few spots are lower than that(crew). And finally the ONE time at the very end when it acted up (fdsa). that was right after all these other runs, so I'm sure it was heat soaked, but I wanted to find out if it had "magically" fixed itself, so to speak, or if it was something mechanical. engine coolant temp seems fine, little higher on the very last one, but not alarming, only 4 degrees higher than what I'm used to seeing.

I do not know! After all that's why I'm posting for help, and trying to provide as much insight as possible so that other may be able to look through the data and maybe catch a trait or two that's recognizable to them. As well no DTCS reported besides the ones for the MAF sensor since I am in speed density.

Once Again Thanks for any help on the matter, feel like the problem is right in front of my face...



Attached Files

Update, it's the next day and it's currently 73 degrees out. So in the middle of my two previous runs, I did make some changes to my VE, mainly adding where I was ridiculously lean, subtracted the knock I found out of the ignition tables, and then with those changes, she didnt quite wanna fire up on her own so I bumped up the base running airflow in park and nuetral by 1. Post logs and reconfigured tune a little later today.

Alright, made it to work and have a few minutes to post up an update. Ambient air temp this morning on the way to work was 73, and steadily increased to about 85 by the time I got there. It cut out just as it did before, I'm really beginning to think that this is somehow temperature related. Just cruising around it seemed perfectly fine as always, and all the way up to 75% throttle I can boost no problem up to about 4PSI. But sure enough as soon as I go WOT and try to go over 4PSI it decided to cut out. Couple side notes:

My A2A Intercooler is 31" x 12" x 3"

When I had the 4lb spring in I had no problems EVER with building boost, reliable everywhere at every ECT.

Though I did notice that in park (no load) I averaged about 180 degrees ECT and when in drive idling at a light I was at about 192 degrees ECT.

Could this possibly be voltage drop from my alternator getting hot? Or a plug that's fouling when it gets hot, or a plug wire? plug wires are just a cheapy replacement from Oreillys, but I feel like it should be working, cause it worked flawlessly last night!!

Can't wait to get this resolved. It's absolutely killing me!!! could it possibly be an ECT compensation table thats adding too much at the higher ECT's?

Thanks again guys!

Here is a cruise/WOT file from today and a new WOT file, as well as the corrected Tune from these files, seems like my VE table is getting more smooth, and during a sharp throttle transition during a different cruise log I had a little more knock (about 1 degree, in a different area than before) so went ahead and took that out.

Attached Files

It initial sounded very much like ignition break up. Given it still runs I would assume it isn't significant pre-ignition, are pistons stock, if relieved did you break sharp edges to avoid hot spots.

It does sound like some form of solid state electrical component breaking down with engine bay heat or intake/engine temp rising just enough for knock. My parents had a car that would develop a missfire at heavy cruise (uphill on a motorway)only after several hours of driving when everything was heatsoaked. Might be time for knock listening/scope on ignition or trigger system.

Good work on providing a lot of description.

The pistons are stock 4.8 pistons, which are flat top. No rough edges anywhere. And speaking of pre ignition, is that what causes the black pepper looking stuff to form around the base of the electrode on the plug? Maybe I need to go to one more cooler range plug. Madea few changes to my PE table and ignition again and it seemed to help, today while driving to work it was about 88 degrees out and I was able to achieve full boost this time but it's still blowing out around 4800 rpm or so. But once again if I do like 75% throttle until I reach max boost, then lay into it the rest of the way, it carrys to redline just fine without issue. Thinking it may be those cheapy wires I got from oreillys.. gonna look at getting a better set with some covers to see if that helps at all.

Holy crap guys!! So, I drove it home, I had made a few changes the guy who made my cam said to try, and it ran even better than any of the other nights so far!! Wow.. I am humbled by this little Hunk O' Junk I built out of my backyard. So when I got home I checked out the engine bay like I usually do while it cools down, but.. I had turned the headlights and I turned on my flashlight and immediately noticed my oil cap was almost all the way off, so I guess a catch can is in my near future? Too much crank case pressure? Anyways I turn off my light and go to shut the hood and I see what I think is a spark. So I hone in on it and then rev the truck when I see multiple sparks where I think it's coming from and I cant believe the light show! Very faint but I could definitely see the arcing. Checked the other wires and none of them were arcing even when revving it. Its #7 (Back, driver-side.) it's touching the valve cover AND it is pretty close to my steering column. Didnt see any arcing on the column though, just the valve cover. So I think I found my issue for sure.. blowing out the spark probably in that cylinder and not burning the fuel which is why I've been showing rich probably at WOT.

So now I spend decent money on a reputable spark plug wire set, that is better suited for my application, and covers. I'm gonna sure as heck try to move the wire away from everything and give it the ole college try. And if it gives me no lip on the way to work then I think I've positively identified the issue.

Missfires will read lean, if you fattened it up to balance a missfire on one the others will be struggling. You will probably find you need to pull fuel out to get to the afr you thought you were at with the missfire.

Sounds like you found your issue at least! It doesn't take too much boost to make these engines really come alive. A decent catch can setup is pretty much a must though as you've found out.

Hey everyone!

Just a quick update, ended up letting it sit for a bout a week straight while I dealt with a death in the family. It has a remote disconnect switch that I turn off each and every time I shut it down. But after sitting a week the battery was dead dead. Could it possibly be that some part of my charging system could be causing this boost cut out? Perhaps because of the dead battery or if the alternator isnt putting out enough juice?? I know it may sound silly, but I've noticed there are a few tables in my tune that do use ignition voltage as one their references. So just another idea I was thing about. Besides replacing the plug wires with decent ones with heat shields, putting in some colder plugs, new battery, and having my alternator tested and possibly replaced. I hope I can find the root of this issue. I sure miss driving my truck


Still cutting out under boost. New optima battery, alternator tested good at the parts store, new 10.5mm wires, with covers. Not touching anywhere, also put in a range colder of plug. I went with the NGK BR7EF's, stock gap (.028"). I'm so confused. I'm almost beginning think it might be something with my tune?? Should I just scrap it and start over from the base file?? I'm stumped on this. Boost quickly raises to about 130-140kpa then falls on its face still. MAP value drops drastically and spark rises rapidly as soon as it does even though I'm 100% throttle. I let off and the BOV let's out the charge. If I go 75ish throttle it doesnt cut out.. any ideas? Spark looked good on the plugs. Fuel ring looks good. I cant seem to figure this one out!! New coils, plugs, wires, fuel pump, injectors, new 2 bar gm map sensor. Still no catch can on this pig, is it possible my cooling system isnt up to par? Or is it possible that since I dont have a catch can set up that its putting too much pressure on the crankcase and its blowing out the spark??Any help is greatly appreciated. Thinking about testing fuel pressure under WOT. Make sure it not dropping or anything will update with results in the morning. Only codes I have are for the MAF fail codes. (Sd tune)

I was reading steady fuel pressure even at WOT before the tune, injector duty cycle is only at 35% or so during full boost. Get back with results on the pressure in the am. Any other ideas would be greatly appreciate it.

New log file and the tune is below.

Attached Files

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