S/C Hesitation at mid-RPM AGAIN

Background: This truck had a very similar issue shortly after I purchased it a year ago with 202k miles. From ~2800 rpm to nearly 4500 rpm, it feels like it's cutting out, hesitating, and maybe even bucking a bit. Above that range the truck quits throwing a fit and really takes off. At the time a member suggested that it may be getting lean and cutting timing. The truck was down all summer for suspension/frame mods so it got a new AEM 340 at the same time. After that, it ran great. No more hesitation, ran just like it should.
Fast forward to last November, a knock sensor went out six hours from home on the way back from a hunting trip. Limped it home at low speed and starting tearing into it after the holidays. It turned into a bunch of maintenance and a few mods out of convenient access while replacing the knock sensors and harness. It included all of the following:

• New OEM Denso knock sensors (had Matsushita before)
• New OEM knock sensor harness
• Resealed coolant crossover
• Valve adjustment. All were in spec, 2 exhaust were adjusted as they were on the low end.
• Resealed valve covers. Half moons, cam plugs, etc.
• Remanufactured Denso injectors from Motorwest
  • Have another thread on this, had a heck of a time getting them to seal up. Eventually they did.
• All new intake gaskets, OEM
• JBA headers

Now the truck is back to the same behavior described above, but worse than before. It's still in the early stages of diagnostics, but here are some details:

• Fuel trims at idle bounce around near 0
• Truck revs to the redline just fine while parked
• Under boost, LTFT goes up to around 18%. STFT stays under 10%. Anywhere else they stay near 0.
• Timing never goes below 9 degrees, most often closer to 13
• No engine codes so far
• Spark plugs are Denso IK22 that were installed at 180k, truck now has 211k.
  • Had time to pull just one this morning. Gaps were at .040 and .050, in pretty good condition visually. The gaps seem a little large, will check more plugs to see where the rest are at.
  • Not sure on age of wires
• MAF reads ~3.8-4.5 at idle, ~.35 with the truck off. Will check values under throttle. Just cleaned it.
  • The truck does have a full K&N intake. Probably not the issue but the MAF might be more accurate on a stock airbox. That's in my plans for the near future.
• AFR O2 sensor voltage values seem to be in range.
• Unplugged the TPS and it threw a code immediately. Would it throw a code if it malfunctioned? I was thinking about trying to drive with it unplugged to try to troubleshoot it.

Any suggestions on where to start? The new injectors are the main change from before, but they were supposed to be an improvement Thanks!

 

Any idea it if has an IAC check valve installed? Helps more than you’d think.

 

The check valve on the IAC hose that's specifically for supercharged trucks? Yes, it does have it. Just verified while everything was apart.

 

Read the symptoms and back in the day that’s what gave a lot of people trouble before that remedy, I’m going to assume it’s installed in the correct direction. The only other thing I can think of is fuel delivery, where bigger injectors or a 7th injector could supplement.

Just my thoughts. You provided all the specs which is good. Hopefully someone else can give some more input.

 

Out of curiosity... have you looked at Mode 6 while having the issue?

 

What is mode 6? My scanner is pretty basic.

 

I'd test that TPS. Seems like its happening in that closed closed/open loop transition.

 

Mode 6 on a scan tool is THE raw data that the PCM is seeing.

 

I'll have to look into a better scanner than my current one to do that. Any suggestions on a reasonably priced one? Maybe one of the Bluetooth ones?
Is there an established procedure for testing the TPS, or is that best done by viewing voltage on a scan tool as well?

New

$7 Denso IK20 Iridium Power Spark Plug, (Pack of 1)

Denso IK20 plugs and Denso wires are on the way. PO said that it had IK22 plugs, but they were the stock ones. Look to be in decent shape but they'll get swapped for IK20s anyways.

 

Before I would invest in a better scanner I would visit my local auto parts store and see what their scanners show for Mode 6 data. Mode 6 data varies from year to year and as it relates to OBDII on 1st gen tacoama's, we are in the dark ages.

If I am understanding all of the prior posts your truck has a supercharger and there is a flat spot. I doubt that the boost is blowing out the spark but you never know. The old school way of handling this is a hotter coil and closing the plug gaps. This is the old days when there was only 1 coil, nowdays, dunno what is avalible coil wise.

I am wondering how the fuel pressure regulator handles positive pressure when under boost and even if it is capable of modifying the pressure beyond what it was designed for.

 

There are some Amazon Bluetooth ones that have the ability to show that data. I'll buy one if this isn't fixed Saturday.

I would guess it isn't blowing the spark out, never heard of that on these trucks. But maybe the IK20 plugs, which are gapped tighter, will help if so.

You probably know, but the FPR is tied to the supercharger so it's supposed to increase pressure 1:1 as boost increases. A 3:1 FMU is probably a good idea that has been commonly used on 5VZ FI applications, but I haven't bothered with one yet. My last supercharged truck (a 1998) never had any of these issues and it was 100% stock aside from the supercharger. Original fuel pump, injectors, etc.

There should be an update Saturday evening with new IK20 plugs and wires.

 

If that doesn't fix it PM me and we can walk through some stuff. I've been through it with these SC trucks unfortunately. The factory ECU gets real screwy sometimes with the SC. You need to look at the AFR sensor to see if it's rich or lean. Sometimes it will run lean but because the ECU has to compensate so far because of the SC it won't add more fuel. Also the knock sensors are active above 3k so it could be pulling a bunch of timing until you get real high in the rpm.

 

@tacoman2001$ thanks for the offer! It was a little surprising, but the plugs and wires seem to have done the trick. The K16 plugs looked to be in good shape, but it seems there is good reason to recommend the move to IK20 or IK22 plugs for the supercharger. The difference was immediate and drastic, it's running better than it has the entire time I've owned it. Both STFT and LTFT stayed much closer to zero, timing stayed in the mid teens, and there is no more hesitation.

 

Maybe I’m going crazy but doesn’t your original post say it’s been running IK22’s for a good 30k?

 

That's what I thought because that's what the PO had recorded in his maintenance log. I didn't know they were K16 until I pulled one out partway through this thread.

 

Good find then! Hopefully the issue is solved.