Need brains, diagnosing supercharged 1GR-FE issue

Hi All, thanks in advance for any input. I have acquired a supercharged 1GR-FE truck but its got a bad stutter around 2000 rpm but runs totally fine at high rpm. These are the poor truck's symptoms

•Hesitancy between 1900 – 2400 rpm (consistent)
•Worse under load (up a hill). Maybe that just makes its lack of go more noticeable
•OBD scanner shows lambda running very lean in that rev range (lambda 1.25)
•Car is taking out advance to protect itself
•AF commanded drops 14.7 to 13.7 but actual goes 14.7 to 18 when it stutters
•Short term fuel trim doesn't vary too much but long term fuel trim is not normal (see image)

Nothing would make the ECU run that lean on purpose. So my thinking is it can only be too little fuel or too much air

1.Not getting enough fuel at a those rpm
•Hardware failure (probably less likely since it takes off up top)
•Injectors
•Fuel pump
•Fuel pressure reg
•Ecu not signalling enough fuel injector at those rpm
•Bad ecu mapping/tuning
•A sensor that causes car to pull out fuelling. 02 sensor? They seem to be reporting numbers which change and are same on each side. Not sure this would only affect one rpm range unless ecu only uses input there.

2.Getting too much air
•Too much boost pressure (or more than ECU expects) for injectors to handle at those revs. Need to check injector duty cycle
•Leak upstream from supercharger. Getting more air than it thinks its requesting with the throttle and seeing at MAF
•Possible that the supercharger bypass valve isn’t working making it develop too much boost down low.

I've attached an OBD scanner output as I go up a hill and the truck bogs down. Point A is where it changes down a gear as the hill starts. Between B&C is where it struggles. The bottom half of the first graph shows how lean it gets and the car pulling advance out to protect itself. The second graph shows the fuel trim which overall is trying to richen up the mixture by a big amount to compensate.

The issue is changing injectors needs the supercharger off and the injectors are expensive. I've swapped the MAF but no difference. Sprayed brake cleaner around but it didn't produce an increase in rpm so probably no leak. I guess I could put a fuel pressure meter on the rail but it runs fine at big rpm flat out. I can't see where my Techstream lets me check the fuel rail pressure.
The two narrow band sensors after the car converter are happy enough at idle flicking between rich and lean nicely. What can make it bog down at lower rpm like this? What is the next thing to check or swap, wide band o2 sensors from a wreckers?

 

Boost is a calculated value in the scanner app so best not to take the nearly 50psi as an actual number, its more about the direction of the levels.

 

Milage?

Have you done the URD fuel pump/filter upgrade/retrofit?

 

Thanks for the input. I think it had been working at some point in its life without this issue. It could be the fuel pump but I haven't thought too much about it because it runs fine at higher revs and full load.

 

I'll be honest, I am by no means a tuning expert, but my understanding is that at wide open throttle, the fuel pump and injectors will be running full tilt whereas at partial throttle and lower RPMs they may not, at WOT the pump may be able to overcome resistance but at partial and lower RPM it's unable to meet demand due to restriction.

My non supercharged truck was having some subtle stumbling issues that disappeared when I did the URD upgrade, the old pump/sock/filter combination module looked visually clogged to me and even compressed air met significant resistance through the filter stone thing.

I would do some fuel rail pressure testing if you could.

Pump was fine but the filter was just done.

Beyond that when is the last time you cleaned the butterfly?

Any intake mods?

Have you cleaned or replaced your VVT-i screens?

 

Thanks, its an 08 with 200,000 miles.
From memory injectors work on a pulse width modulation so I'd assumed that because they can do big open % they can do a smaller open % but maybe my assumption is wrong. At high rpm I can floor it and come off and floor again and it runs like a scalded cat. Checking the fuel rail pressure isn't anywhere near as problematic as swapping injectors so maybe that is next to rule out the pump and lines. No intake mods, have never cleaned the VVTI screens.

 

I would want to monitor both the upstream AFR sensor and downsteam O2 sensor on both banks, many times you can use the downstream to tell if the upstream is lying. Fuel pressure would be another good thing to check when the problem is occuring. Also I see your long term trim is pegged at around 29% at the beginning and end of the graph, you may want to look into that further (normal Total trim (long+short) should stay around +/- 10%).

 

@12TRDTacoma

 

I don't see this mentioned - have you thoroughly checked for vacuum leaks? Not just visual, but with brake cleaner or starting fluid while running? If you're getting the commanded AFR but seeing much leaner AFR's, combined with the off idle stumble, I'd look for vacuum leaks first.

 

With that many miles, you should strongly consider upgrading the fuel pump. Strongly.

First thing that came to my mind, was what @Fullboogie said. Check every vacuum hose.

 

It's not complicated. Get a new pump and filter.

 

I second what he said. ^^^

 

If you really want to fix this properly then you need to identify the root of the lean issue first. The MAF is always my first go to when I see that much lean activity. However, given that it's MEGA lean as indicated by the PCM my next go to is the fuel pump. If you want to confirm proper fuel pressure you need to hook a fuel pressure gauge and take it for a spin to duplicate that hesitation at lower RPM range.

The pumps on these trucks are known to fail, particularly on the later gen 2nd gens. Once you are hooked up, you need to see 41.7 PSI upon cranking. If you see 20 or anything that is below that, you found your problem right there. After you replace your fuel pump make sure you disconnect the battery for a few hours then reconnect to reset the adapted running condition this will fully reset trims to zero and you can restart.

Make sure you monitor the fuel trims closely upon your next drive after your fix (whatever that will be). I had a NA 2015 Tacoma once that was running lean with an Air fuel ratio imbalance bank 2 code, I can't remember the exact code label, but had proper power across the band. What ended up happening was that the fuel pump failed due to faulty injectors which were running hot so you could see the nozzles on a few of them scorched. However, the intermittent fuel pump lean stutter was caught after replacing the injectors.

I hope this helps, and good luck. Keep us updated and let us know what you find.

 

Thanks to all replies, super useful.
@12TRDTacoma (&Lucario) I've swapped out the MAF and no change. I will do the fuel pressure rail check first. I had assumed that because its fine at big rpm it couldn't be this, but sounds like the wrong assumption. Hopefully there is a simple port to plug a gauge in to. Fuel pump not an expensive swap in any case.
@Fullboogie I sprayed brake cleaner around but didn't see much change. When I sprayed some into the throttle it took quite a bit to get it to change rpm so maybe a small leak wouldn't have been detectable. Because its running lean I took a look at all places between the MAF and supercharger because if it was going to get more air into the cylinder without the MAF measuring it I thought the leak would be there. If the leak was between supercharger and cylinder it would be getting less air not more. But it sounds like you are saying to check a bunch of other hoses as well?
@Dm93 I did consider the o2 sensors, they do seem to be both the same reading at idle between the narrowband sensors downstream of the cat and the widebands between engine and cat. It is possible that the widebands are reading wrong at other AFRs. Both banks read the same so no obvious issue with just one of them.
Might seem a bit much but I created a flowchart to get my thoughts straight. Only other thing I could see was the boost does seem to rise very quickly which could lead to a lean issue but I don't know much about how an ECU controls supercharger boost.

 

bad signaling from ECU to injectors

wrong timing on injectors

insufficient flow at injectors

corrupted tune

 

There is no fuel pressure tap, you would have to tee in a gauge.

If you have no bank to bank imbalance then it's very unlikely to be bad O2 sensors.

Boost would have to be a calculated value because the 4.0l has no manifold pressure sensor.

Do you know that everything was done correctly when the S/C was installed? There's more to an install than just the S/C, you also have to put different injectors and spark plugs (usually these are provided in the kit) and flash the ECU with a supercharger tune.

If you think it may be something with the tune you might get with @JustDSM he is one of the tuners that lurks on here, he may know what to look for.

 

I had a similar issue a while back on my SC 1GRFE (Magnusson/TRD) with over 200k miles. Was running way lean at part throttle (17-19afr)but at WOT throttle was normal. I was thinking it was the MAF sensor so replaced it but still the same issue. Problem ended up being the vacuum hose connected to the bottom of the supercharger housing was dry rotted and split. Replaced the hose and fixed the problem.

 

A lot of possibilities here. The info I gave you assumes you have ruled out vacuum leaks first. If you have access to a smoke machine, definitely use it! Those things are SO useful.

Air fuel ratio sensors are a possibility, but somewhat unlikely, as you would have a code for it most of the time and the sensor would affect throughout the operating range.

You never did state the miles or the year of the truck, that much I'm curious of.

Oh one more thing. To check fuel pressure you can just pull the fuel line off by the supercharger on the driver's side. You can literally disconnect it with your hand. No tools needed.

 

Smoke machine is definite must when tracking down a lean condition. That's how I found the split vacuum hose.

 

I have repaired this as well for a fellow s/c owner. Boom back to awesome.