3sgte 3sgte hesitation and mis-fire under load

[basher590]

Hey Everyone, 

I've been lurking on the forums for a while but yet to post. I am trying to diagnose an issue with a freshly built Gen2 3sgte with forged internals. 

I know there are a lot of posts on here with the same heading and I have read them all and tried quite a few things, but I have reached the limit of my knowledge and could do with some ideas or new avenues to investigate. 

Description:

When  >75% throttle the car feels like it's hesitating, and misfires 1 to 3 times on a pull. The more throttle you give (and from lower down the rev-range) the more misfires and the worse the hesitation feels. The car is also not making full boost anymore, it was hitting 17psi no issue but now tends to go anywhere from 7 to 10psi max. 

Part throttle and it revs out fine and doesn't feel like it hesitates. 

The car has been driving very well since the rebuild and this issue slowly started to creep in over the last few months, getting weaker on power and eventually now mis-firing. 

Car:

ST185 3sgte. Freshly(ish) built bottom end, forged pistons. Rebuilt head to standard spec. (has done 1k miles since rebuild)
clocked, Hybrid turbo
Front mounted Intercooler with custom welded/polished pipework
External Oil Cooler
Larger ally radiator
Larger fuel pump (I forget the size), 800cc injectors, rail, pressure regulator
G4+ Monsoon
Air filter/downpipe/exhaust etc

Actions taken so far:

So I have replaced a lot of things and changed a lot of things... 

Replaced:

Alternator, plugs, leads, dizzy cap, rotor arm, coil, wiring to coil, injectors and ECU (all now on the same circuit), All earths/ground straps replaced with new, heavy duty crimped cable. 
Serviced the turbo, replaced the shaft, turbine wheel, seals and bearing (by a professional turbo company, Midland Turbo)

Checked/Changed:

changed dwell time
pulled some of the ignition timing
boost control to try and increase boost pressure (no change)
Compression test when warm: 150psi on all 4 cylinders (this is low but within book spec, which is 140 to 185psi) I am guessing that because it's forged pistons it's lower overall cylinder compression, typical 3sgte is mid 170's, could this be the issue? I'd have thought as all 4 are identical this isn't it). 
No trigger errors or any other errors reported by the ECU

Re-plumbed the PCV system so it's pulling gasses out of the head now and back in via the intake (pre-turbo) - it was vented to atmosphere via a catch can, and I checked there weren't any blockages (which there weren't), this is pulling a vacuum now at the head when revving with the oil filler cap off.  (there was oil in catch can, more than I'd have expected for such low miles but not loads). Pre, making this change the turbo intake had a small amount of oil in it and nothing else was plumbed into that side so it must have come from turbo oil seals, hence  re-plumbing the PCV system. I've not yet checked for crank case pressure, unsure how to do that without welding a bung onto the sump pan to fit a pressure sensor. 

I have attached a log file of a single pull that has a few misfires in it. Let me know if anyone wants the map as well. 
Do these look like mis-fires? Does anyone see anything untowards in the log or things I can check/change? 
https://drive.google.com/file/d/1iSH_Dyf_JvAEKBypBBbStOly5LyYQcOL/view?usp=sharing

Things to do next:

Try replacing the turbo for a new or known good unit (since oil seals are maybe gone)

Do a CoP conversion

Replace distributor (reconditioned) or with a trigger wheel
 

Conclusion / Ask:

Rather than carry on replacing things and throwing money at it, if anyone has any ideas to help me debug and pinpoint the actual issue that would be really helpful.


 

[Adamw]

At around the 1 second mark and again at around 3s in the log there are is a sudden spike/loss in MAP, the 2nd one shows it lost 25kpa in 0.03s which is only 1 log sample, so in reality it was probably a much bigger loss.  The turbo speed couldnt change that fast if the wastegate was doing something funny so I would say the pressure loss must be caused on the intake side.  Is there a BOV that could be popping open?  Otherwise look for things like a split pipe coupling or air filter collapsing etc.   

 

[basher590]

Hey,

 

Thanks for the info. There is a BOV, but I have tried another one.... though I could remove it completely to test, that's a good idea. 

I did do a pressure test on the pipework up to the throttle body (should have put that in the original thread) and that's holding pressure fine. I tried to do one on the inlet manifold, but it was leaking through the valvetrain so made it hard to hold any decent pressure, though I didn't detect any leaks. 

Those are spikes/troughs in the log file are what I am interpreting as a misfire, do they look more like a sudden loss of pressure then? They wouldn't explain the lack of power/hesitation though? (Perhaps I have 2 problems). 

I'll have another look over the pipework and remvoe the BOV for a test, thanks. 

Edited June 7 by basher590
added question around misfire/hesitation reflected in the graph

[basher590]

Sadly no change, it's still exactly the same, very hesitant and those same misfires when >75% throttle.

I have removed the BOV and I also removed the boost controller for good measure so the wastegate actuator is plumbed directly to the turbo.

I checked the air filter for signs of crushing under vacuum, but I don't see any and I'd be very surprised if it is... it's a new Apexi cone, it's very strong/robust under my own squeezing and all the pipework pre-turbo is steel. 

I looked over all the intercooler pipework and manifold vacuum lines for leaks, but none there (I pressurized as best I could with a large bicycle pump and sprayed soapy water around all the hoses and joints and didn't see any bubbles. I did manage to get out about 3 psi of pressure from my hand pump.

 

This could just be me but it doesn't feel as bad when I first pull out the driveway, it seems like it's going to be OK but as it warms up it gets worse. I obviously don't give it much boost/throttle until it's fully up to temp, so hard to tell if I am just being overly sensitive/optimistic.

I guess the next step is to get a proper compressor and see if I can get ~15 psi or more on the intake. 

 

forgot to say, I also replaced the igniter with a 2nd hand one and that didn't make any difference. You can't get new ones anymore and the blueprint one I got didn't work at all despite being the correct part number. 

[basher590]

I rewired the lambda sensor this morning because it stopped working, doing a bit of diagnosis with the multimeter there were sporadic voltage drops across the EFI Main Relay circuit that only really powers the lambda, ISCV and fuel pump now. So I rewired that and it's more stable now. 

I made a minor adjustment to the dwell times and went for a drive and initially it was driving really well, much smoother, no hesitation and made boost (still actuator pressure) very easily. However as it got warmer the hesitation started to come back and I got 1 misfire event. (Are these misfires?) 

I have a couple of questions.

1. There is a misfire event at 3:11 in the logs. This shows a brief spike in manifold pressure followed by a drop, as is typical with these events I am experiencing. This is then followed by a drop in lambda (rich condition). Does this drop in lambda point to the spark being blown out and the mixture not properly igniting? If so would that explain the manifold pressure spike and drop? 

2. At that same time (3:11.037) the dwell time goes beyond what's set in the table, it hits 4.72ms, even though dwell max is set to 4.5ms. Does this really matter is it a red herring?

Log File: https://drive.google.com/file/d/1c0hkwd-WimQi08FXjHTtRljIfJbpyPq4/view?usp=sharing

Map: https://drive.google.com/file/d/1h2Rjvyrh6vYIYJFTQDyIDv7agGSLI19j/view?usp=sharing

[servicesoon]

Which spark plugs and what gap?

[Adamw]

On 6/9/2024 at 10:22 PM, basher590 said:

This shows a brief spike in manifold pressure followed by a drop, as is typical with these events I am experiencing. This is then followed by a drop in lambda (rich condition). Does this drop in lambda point to the spark being blown out and the mixture not properly igniting? If so would that explain the manifold pressure spike and drop? 

Usually lambda shows lean when there is a misfire as you have uncombusted oxygen pumped through the exhaust, that is not always the case though. My logic would say the rich spike is possibly more due to the drop in MAP, you have already injected fuel into the intake port based on the higher MAP, so if MAP is suddenly lost somewhere you have too much fuel injected for the amount of air that gets ingested.  A drop in MAP also evaporates more of the fuel puddle at the same time.   

 

On 6/9/2024 at 10:22 PM, basher590 said:

At that same time (3:11.037) the dwell time goes beyond what's set in the table, it hits 4.72ms, even though dwell max is set to 4.5ms. Does this really matter is it a red herring?

My general rule of thumb is +/-0.3ms is acceptable with a cam based trigger.  If the crank suddenly slows down after the dwell period has been started, then the ecu needs to stretch out dwell to ensure the spark occurs at the correct angle.  

 

I dont see any obvious clues for the cause of your hesitation, but here's a couple of suggestions that would eliminate some possibilities and give a general  improvement:

1. Your lambda is all over the show, rarely anywhere near target.  A lot of that is caused by overactive accel enrichment because your deadband is set to zero.  So that needs to be fixed and a lot of your fuel map will likely need re-tuning after that.  But I think there may also be some other issue causing further variability.  I would add a fuel pressure sensor so that can be ruled out. 
2. I would double check rotor phasing, based on your trigger offset it should be ok, but you never know with aftermarket distributor caps etc.  Instructions for this check are in the help file: Wiring Information > Output Wiring > Ignition Drives > Distributor Ignition
3. While you are messing with the distributor I would also do a check to confirm the offset is resulting in the correct injector timing.  A quick test for this is to temporarily change your ignition mode to direct spark, (unplug the fan relay since that is wired to ign 2), pull cyl 1 spark plug lead off and ground it with an old spark plug, then crank it over and check if you have a spark on that plug.  If not then the offset is wrong, change by 180 or 360 and test again.  
4. The last suggestion I have is I would strongly consider upgrading to COP, you can wire them in wasted spark since you are running low on outputs.  The reason for this is distributor ignition just has so many potential issues, getting rid of the distributor cap, leads, cross talk, rotor phasing, high voltage next to the trigger sensors, all the spark leakage points, ignitor, condenser, etc rules out a whole lot of possibilities and even if it isn't part of your current issue, it will likely improve only reliability in the future.  You can get a set of VAG coils for <$100USD in 3 different lengths and they usually dont even need a bracket to mount.      

[basher590]

On 6/12/2024 at 8:38 PM, servicesoon said:

Which spark plugs and what gap?

I have tried a couple diff new ones, BKR7E-GS, and BKR7EIX, they're 0.9 and 0.8mm respectively, but they didn't make much difference. (Book spec is 0.8-1mm)

Thanks @Adamw for the info, that's super helpful, I will work through that over the next few days (may be weeks as I am going away shortly) and post my findings back here. 

I appreciate the advice, thank you. 

[servicesoon]

Are you rocking a hybrid CT26?

Last year I dynoed 385whp w/ stock distributor. As long as your distributor and single coil are in good condition they should not be your issue. I did have to close my spark plug gap to 028. Looks like you are already 1 heat range cooler than stock. 

[koracing]

FYI the dwell on the Gen2 3SGTE igniters (usually a blue or green label on the igniter 88-89 ST165, 90-93 ST185s, 91-95 USDM Mr2, 90-93JDM MR2) don't matter that much as they have dwell control built in.  You just need to give a signal big enough to trigger the igniter from the ecu.  Most times on gen2 engines with stock igniter I just use a flat 2-3ms dwell table.  For up to 20psi boost a gap of .025-.028 inch works well.  For more than 20psi and up to 30psi I gap to .020-.022" on the 3SGTE.

Upgrading just the coil to an MSD Blaster SS coil as the only ignition upgrade (assuming good wires and BKR7E plugs, and ideally Denso cap and rotor) I've had no problem getting to 600whp on ethanol tunes on built 3SGTE engines.

Double check your trigger arming thresholds at various rpms also just in case.  Trigger scopes at cranking with the stop switch dignital input set to "always on", and at 1000, 2000, 3000, 4000, 5000 etc.  Make sure the Trig1 and 2 arming are set to about 1/2-2/3 of the nominal peak voltage of those trigger scopes at each rpm and that you're not seeing artifacts of noise in the trigger signal.

EDIT: G4+ Monsoon can't do trigger scopes.