jimxms

My tuner seems to be having issues getting my Z51 dialled in properly after it came back from having pistons, stage 3 cam, valvetrain and LT4 fuel system installed.

At first we had problems getting it to start and idle, but this has been resolved in the tune. Now we have hit a roadblock where the car stumbles, pops and backfires during medium and above acceleration. My wideband shows that it is running rich (between 10 - 11 afr) but my tuner is telling me that the narrowband readings are correct and he doesn't want to pull any more fuel. The accuracy of my wideband has been called into question, but it only has 500 miles on the sensor and reads ~14.7 at idle.

The tuner is well respected on here and I won't say his name unless he wants to chime in, but I'm really at a loss as to where to go from here. This is a full run-down of my mods:

Procharger D1-X Supercharger (not even gone into boost for tuning yet)
MSD Atomic Airforce Intake Manifold
Vengeance Racing Forged Pistons
Vengeance Racing Stage 3 Camshaft (+32% fuel lobe)
BTR Dual Valve Spring kit w/ Titanium Retainers
Vengeance Racing Hardened Pushrods
C5R Timing Chain
Brass Bushed Rocker Arm Trunions
LS7 Lifters
Top Speed Decat Long Tube Headers
Borla Decat X-Pipe
LT4 Fuel Pump and Injectors
Mighty Mouse Catch Can
WeaponX Valve Covers and Coil relocation Kit
ARP Bolt Kit
SacCityCorvette Billet Oil Diverter Barbell
AirAid 6” Trackday Air Filter
MSD Ignition Coilpacks and Spark plug wires
NGK LTR7IX-11 with 0.035” gap

Ben@WeaponX

I got notification due to our valve covers but I'll gladly throw some ideas your way with a short list to check the low hanging fruit!

1. Even if your WB is at 14.7 at idle, you should still always calibrate it before tuning. That being said, I doubt this is your issue unless you're insanely lean.

2. So, your STFTs are +/- 5%ish? If not, you might have burned up the harness or wiring going to them. If your STFTs aren't adding fuel, then I would doubt your WB is off.

3. Are you getting any CELs or misfires pointing you to any specific cylinder (s)? DI rail pressure on target? etc?

4. Pull and inspect every spark plug wire to see if any were burned through on a primary. This is one of the most common problems.

5. Pull and inspect every spark plug to see what the tips look like and ensure there is no cracked porcelain or closed tip. Reinstall with diode grease if not done so previously.

6. Did you verify the preload on the LT4 DI pump? This is very important and one of the most overlooked things by most people. It's just like a lifter, you have to be around .040 (including the gasket).

7. Did you verify the preload on the lifters? Also, you guys running boosted applications, I can't stress enough how important good lifters are like a Johnson 2116 or 2126.

8. Lastly, ask your tuner if the cam timing is as commanded to verify proper operation of the phaser if needing to be locked out at WOT.

Good luck!

jimxms

Thanks man. I can only answer a few of these as I didn't do the build myself, but maybe it will help....

1. I'm using a Zeitronix W/B which doesn't let you manually calibrate

2. I don't know - How do I found out what my STFT's are? I've checked the wires of the NB sensors and they both seem OK with no visible damage.

3. No CEL's - but I understand that misfires have been disabled in my tune. I know my tuner said he was going to re-enable them to see if it threw up anything obvious.

4. All Spark wires are OK. I Installed a fresh set and have the DEI titanium boots over them to keep them away from the headers.

5. I had the spark plugs out a few days ago and I checked the gapping on them. They seemed black/sooty (rich?) so I cleaned them up with a soft wire brush and some brake cleaner.

6. I asked my builder to pay extra attention to this and printed off the instructions on here written by fyreant for him to follow. I noticed this in his build notes if it makes any sense to you:



7. Thats a new one to me. How is that performed? I have LS7 lifters, are they OK for boosted?

8. Thanks I've asked my tuner and will see what they say.


For what its worth, I just took the car out for another drive after my tuner had pulled some fuel. The car doesn't seem to like 'regular' driving very much. Medium throttle in 2nd/3rd results in a put-put-put-put exhaust note up to about 3k RPM with very little power (feels like its being held back). After 3k the exhaust note smooths out a bit and the power comes back and it takes off. This is all with no positive boost from the procharger.

If I throw caution to the wind and just stick my foot to the floor in 2nd/3rd the second the car hits positive boost, everything is perfect.

If my Zeitronix is to be believed, I'm still seeing AFR's as low as 10.6 during normal driving. I can't put my finger on what conditions reproduce that scenario tho.

Ben@WeaponX

Answers below

1. I'm using a Zeitronix W/B which doesn't let you manually calibrate

OK, did you look pull out the WB and NBs? I'd inspect the sensor tips if your plugs were that fouled.

2. I don't know - How do I found out what my STFT's are? I've checked the wires of the NB sensors and they both seem OK with no visible damage.

This is in the tuning logs, but if you have a simple OBD2 reader like the iOBD2 ($30 on amazon), you can download the app and select the PIDs to monitor on your phone if you don't have HP Tuners. If you do have HPT, I can email you a config file to send me a log. Now, I'm not offering to tune your car as you already have a tuner, just trying to help solve your problem as I trouble shoot a lot and quite frankly, enjoy it. LOL

3. No CEL's - but I understand that misfires have been disabled in my tune. I know my tuner said he was going to re-enable them to see if it threw up anything obvious.

You def need to have everything on in order to diagnose something like this, well... with the exception of your secondary 02s etc that need turned off with headers. But we need to be able to pinpoint a cylinder or more broadly diagnose if misfires are in multiple cylinders.

4. All Spark wires are OK. I Installed a fresh set and have the DEI titanium boots over them to keep them away from the headers.

I would inspect them again, just because you have boots on doesn't mean that they didn't get hot somewhere. The C7 bays are cramped and we see burnt plug wires frequently on LT1 and LT4 engines.

5. I had the spark plugs out a few days ago and I checked the gapping on them. They seemed black/sooty (rich?) so I cleaned them up with a soft wire brush and some brake cleaner.

Put new plugs in LOL

6. I asked my builder to pay extra attention to this and printed off the instructions on here written by fyreant for him to follow. I noticed this in his build notes if it makes any sense to you:

I am not sure what the terms "pump top" and "gaps" mean haha and I've never compared it to crank degress as the cam fuel lobe needs to be at base circle, but if this says the preload is .037 with the gasket, then you are good.

7. Thats a new one to me. How is that performed? I have LS7 lifters, are they OK for boosted?

Whenever you're doing a cam, you ALWAYS need to measure lifter preload. Core shift on blocks, decked heads, etc all come into play and too little or too much preload and you run into detrimental issues like valve float, pushrod flex, or worse... a collapsed lifter which will usually take out your cam lobe. That's why we run the Johnson's too, short travel slow leakdown axle oiling make for great power! Too late to swap though, heads would have to come off. LS7s are used frequently, but I can tell you with absolute certainty the Johnsons are worth the cost from our testing

8. Thanks I've asked my tuner and will see what they say.

For what its worth, I just took the car out for another drive after my tuner had pulled some fuel. The car doesn't seem to like 'regular' driving very much. Medium throttle in 2nd/3rd results in a put-put-put-put exhaust note up to about 3k RPM with very little power (feels like its being held back). After 3k the exhaust note smooths out a bit and the power comes back and it takes off. This is all with no positive boost from the procharger. If I throw caution to the wind and just stick my foot to the floor in 2nd/3rd the second the car hits positive boost, everything is perfect. If my Zeitronix is to be believed, I'm still seeing AFR's as low as 10.6 during normal driving. I can't put my finger on what conditions reproduce that scenario tho.

The fact that your car seems to be operating fine when entering PE mode, does point to some of the previously mentioned potential problems; however, your trouble shooting will be much more precise and quicker with proper data logging as your misfire counts and CELs will either tell you that it is a single cylinder to narrow down the potential problems, or that it's across all cylinders or a certain bank, allowing you to exclude some of the aforementioned culprits.

jimxms

Thanks again man, some comments:

A) I will inspect the NB and WB tips - I assume that they will just need cleaning?
B) I will also buy a new set of plugs - Shall I stick with the NGK's I was using before, or switch to a different plug?
C) I have attached a log of a drive from earlier today - maybe it already has the info you need? If not please send email me the log config - I really appreciate this.
D) I will get the tuner to re-enable misfires asap.
E) I am 99% sure the wires are fine as this has been going on for some time and I've had new wires in between (when I put the valve covers on). I will check again when I replace the plugs
F) Did the image in point 6 for the HPFP make any sense to you?
G) If measuring of the lifter preload is standard procedure for rebuilding any LT/LS engine, then I'm fairly certain my builder will have done it as they have been in the business a long time. I will ask them though.

Ben@WeaponX

A) I will inspect the NB and WB tips - I assume that they will just need cleaning?
I don't know the procedure to clean, we just replace

B) I will also buy a new set of plugs - Shall I stick with the NGK's I was using before, or switch to a different plug?
we run Brisk Silver plugs

C) I have attached a log of a drive from earlier today - maybe it already has the info you need? If not please send email me the log config - I really appreciate this.
will comment below

D) I will get the tuner to re-enable misfires asap.
ok

E) I am 99% sure the wires are fine as this has been going on for some time and I've had new wires in between (when I put the valve covers on). I will check again when I replace the plugs


F) Did the image in point 6 for the HPFP make any sense to you?
not how we do it, but not saying it isn't right. we have a preload calc sheet that automates it all based on our inputs as well as custom made dial indicator gauges to check this on every cam install

G) If measuring of the lifter preload is standard procedure for rebuilding any LT/LS engine, then I'm fairly certain my builder will have done it as they have been in the business a long time. I will ask them though.
i would assume so as well, but life is safest when you "trust but verify"

OK, looking at your log, here is what I notice:

The bad
Manifold Air Temp - this is all over the place and a calculated value indicating AFR parameters are giving this calc fits, which will cause your timing to be all over, resulting in jerky feelings
EQ error is all over at steady state cruising out of PE
SFTF Bank 2 is erratic which is what you need to be paying attention to. STFT B1 is 0% and B2 is more frequently trying to pull fuel in the 10% range. This is telling me that B1 fueling is close to accurate, but B2 is trying to pull fuel out for being too rich.

The good
Fuel line pressure looks fine
Fuel rail pressure looks fine
Injector M/S are in sync

I would venture to bet you just need to replace your plugs or passenger NB 02. If you have a cylinder with a cracked porcelain spark plug, burnt wire, bad coil pack or not connected, etc, you have unburnt fuel going past the NB 02 on B2 and as a result, it's trying to pull fuel, causing a lot of erratic results, or bad NB 02 sensor or burnt wire/harness causing erratic results.

jimxms

Thanks for taking a look, at least it sounds like the fuel pump has been installed correctly.

It is about 6c ambient today, could that be an attribute of the massive temperature swings? Is the manifold air temp taken by the MAF? If so, I have a break-out cable for the BARO and AIT (AIT sensor is drilled into the intake manifold).

Any chance you can hit me up with the price for some Brisk plugs and two new NB o2 sensors?

Ben@WeaponX

Baro, IAT reloca, or low ambient won't affect MAT calc like this. It's a calculated temp, so the variance tells me one of the parameters (or more) in the algorithm aren't getting accurate/consistent data. MAT line looks like a mogul haha

New sensors you can grab from GM, I don't sell them, we just pull locally ourselves.

Brisk: https://weaponxmotorsports.com/produ...=1321031761947

Keep me posted.

Ben@WeaponX

Actually, it looks like your misfires are on, Cyl 2 front pass bank is the problem, which corresponds to the narrow band B2s being erratic.

1. Check to make sure coil pack is plugged into the harness well.
2. Check both ends of plug wire to ensure plugged in well
3. If #1 and #2 are OK and you don't have another spark plug wire, you can first swap Cyl 2 wire with Cyl 4 wire and log to see if misfire count moves to Cyl 4 - then it's the wire
4. If #3 doesn't move the misfires and you don't have another spark plug, you can swap Cyl 2 plug with Cyl 4 plug and log to see if misfire count moves to Cyl 4 - then it's the plug
5. If #4 doesn't move the misfires and you don't have another LT coil pack, you can swap Cyl 2 coil pack with Cyl 4 coil pack and log to see if misfire count moves to Cyl 4 - then it's the coil pack

I have a feeling you're going to find a hair line crack in the spark plug porcelain that is causing all of this.

jimxms

KemahGT

It shouldn't make a difference if these are the down stream O2 sensors. They may be turned off in the tune. These are usually just used to verify the operation of the cats. All tune corrections are made from the upstream O2 sensors.

jimxms

New spark plugs, new o2 sensors, new MAF and a dual sensor wideband all on their way to try and get to the bottom of this.

I had about 30 mins this evening before dark to check on the coilpacks, and they are all working fine. That bloody fuse box gets in the way of quickly checking anything else

jimxms

OK Ben, I gotta give you a pat on the back because I pulled my spark plug wires and found this on the passenger side front of engine (furthest from firewall):



It looks like my headers are not properly designed as it is impossible for me to put a spark plug boot in that cylinder without it directly touching the header:



It looks like my DEI titanium covers were merely transmitting heat directly to the rubber plug boot. Which poses my next question...how do I fix this!!!

With it actually touching I'm assuming any heat barrier material will be ineffective?

Poppacapp

Do they have a 45 degree boot available?

Poppacapp

And props to you Ben. It's nice to see a vendor helping a forum member without them being a current customer for the sake of just helping someone. I am just a basic beginner on the tuning side(my car only track tweaking etc), but I thoroughly enjoy seeing the troubleshooting process from experienced tuners and builders.

jimxms

C5-VERT

I was going to say check plugs and wires also. I had a crack in the porcelain in mine and that was enough to make it do the exact same thing. Get some spark plug heat shields like mine, I have same wires and ordered these for heat protection working great!

jimxms

Yeah I've got a set of those heat shields (well the DEI titanium ones). I think they was probably just transmitting the heat straight to the spark plug boot as there was direct contact between the header and the shield.

I'm looking at a set of ceramic spark plugs right now as it looks like I'm going to have to replace them anyway.

Off topic: where did you get your Procharger inlet tube from, and are you running direct injection still on your ride?

FYREANT

FYREANT