Lean Misfires at 2700-2800 rpm - Page 58 - 3000GT/Stealth International Message Center

ProwlerGT · 11-09-2007, 02:34 AM

Quote:

Originally Posted by DoctorDex

I think oscilloscope is the next step (if I can't convince my friend).

Its late and I'm tired and I've had a stupid idea that maybe the pressure pulsing and missing are somehow related?

Here's why: If you have a cylinder that doesn't fire and there is no fuel dumped into the exhaust then the this would cause the turbo to temporarily slow down. Could this be causing the pulsing?

I wish I could say for sure man, but I have no idea what pressure pulsing is or means. lol - Swiss cheese knowledge. What you said just leads me to ask:

Why wouldn't the cylinder fire and what would it be that would be the same for other people with the same problem at the same RPM range?

How could there be no fuel dumped if the cylinder isn't firing? This would be good to watch with the exhaust OFF.... but better have some damn ear plugs.

Vehicle speed sensor - My thought with that comes from the predictability of when the missing occurs. What if in that range the speed sensor is unable to distinguish (or is reporting a wrong voltage to the ECU) the vehicle speed.... wouldn't this mess things up?

Its too bad moving your engine into a 2nd gen vehicle would be really hard to do..... it would iron out whether its mechanical or electrical at least.... surely a very BIG task to undertake just to find that out... would be much easier to just try your ECU in your friend's car. lol

DoctorDex · 11-09-2007, 07:37 AM

I can't see it being the speed sensor as the car also misses in neutral.

The reason I'm thinking the cylinder isn't firing is because fuel isn't getting into the cylinder. This could be either because the ECU isn't telling the injector to fire, the injector just isn't firing or the valve isn't opening far enough to allow the fuel in. The reasoning behind this thinking is because the missing was "fixed" by spraying a tonne of methanol while driving in the miss range. This means that spark must be good and air flow is probably good.

This is why I'd like to get my hands on an oscilloscope, so I can see what each individual injector is doing during the missing.

StealthCRF · 11-09-2007, 11:51 AM

take hose crimps and try blocking off your vent hose/solenoid and making sure you don't have any evap system leaks

DoctorDex · 11-09-2007, 12:45 PM

Quote:

Originally Posted by StealthCRF

take hose crimps and try blocking off your vent hose/solenoid and making sure you don't have any evap system leaks

I've done a vac. reduction, so while the car is off my evap system is closed off. When the car is running and in vacuum, vapors are pulled from the tank into the preturbo (pre-MAF) intake pipe. This shouldn't have any effect on how the car runs. Thanks for suggestion though.

ProwlerGT · 11-09-2007, 05:17 PM

Quote:

Originally Posted by DoctorDex

I've done a vac. reduction, so while the car is off my evap system is closed off. When the car is running and in vacuum, vapors are pulled from the tank into the preturbo (pre-MAF) intake pipe. This shouldn't have any effect on how the car runs. Thanks for suggestion though.

When you are running a full tank is it possible liquid gas is getting sucked into the intake? or is there enough clearance for it to always only be gas vapor?

DoctorDex · 11-09-2007, 10:11 PM

Pretty sure its just gas vapor.

StealthCRF · 12-14-2007, 07:48 PM

Doctordex. was taking my last class for mitsu "master elite technician" status this week and was talking to some trainers and engineers from MMC about your problem. The only thing anyone came up with that you haven't covered is valve springs upside down

I know that sounds silly and far fetched but mitsubishi uses a harmonically tuned valve spring that will cause valve float around 3k rpm if inverted. the side with more twists of spring goes down.

DoctorDex · 12-14-2007, 08:17 PM

Thanks for the suggestion.

I've been wondering about some sort of valve issue, especially with the ticking noise I get from my rear valve cover. It doesn't really seem to fit 100%, but then again, nothing seems to fit 100%. I suppose maybe an intake valve could be floating/sticking resulting in only 1/2 of the required fuel getting into the cylinder??

badass3000 · 12-14-2007, 08:35 PM

if this is an upside-down spring I will eat my sparkplugs, all of them.

DoctorDex · 12-14-2007, 08:41 PM

Quote:

Originally Posted by badass3000

if this is an upside-down spring I will eat my sparkplugs, all of them.

lol. +1.

How are things with your car coming along? Do you have it back together yet? I'm interested to see if any of the changes you've made have helped.

11-09-2007, 07:37 AM	#572 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Edmonton, AB Drives: '91 VR4 - RIP Trader Rating: (14)	Re: Lean Misfires at 2700-2800 rpm I can't see it being the speed sensor as the car also misses in neutral. The reason I'm thinking the cylinder isn't firing is because fuel isn't getting into the cylinder. This could be either because the ECU isn't telling the injector to fire, the injector just isn't firing or the valve isn't opening far enough to allow the fuel in. The reasoning behind this thinking is because the missing was "fixed" by spraying a tonne of methanol while driving in the miss range. This means that spark must be good and air flow is probably good. This is why I'd like to get my hands on an oscilloscope, so I can see what each individual injector is doing during the missing.

11-09-2007, 11:51 AM	#573 (permalink)
StealthCRF Gixxer Fixer Join Date: Feb 2002 Location: Dallas/Fort Worth Drives: on empty Trader Rating: (4)	Re: Lean Misfires at 2700-2800 rpm take hose crimps and try blocking off your vent hose/solenoid and making sure you don't have any evap system leaks __________________ 92 Stealth RT/TT Best time: 13.2 @105

11-09-2007, 10:11 PM	#576 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Edmonton, AB Drives: '91 VR4 - RIP Trader Rating: (14)	Re: Lean Misfires at 2700-2800 rpm Pretty sure its just gas vapor.

12-14-2007, 07:48 PM	#577 (permalink)
StealthCRF Gixxer Fixer Join Date: Feb 2002 Location: Dallas/Fort Worth Drives: on empty Trader Rating: (4)	Re: Lean Misfires at 2700-2800 rpm Doctordex. was taking my last class for mitsu "master elite technician" status this week and was talking to some trainers and engineers from MMC about your problem. The only thing anyone came up with that you haven't covered is valve springs upside down I know that sounds silly and far fetched but mitsubishi uses a harmonically tuned valve spring that will cause valve float around 3k rpm if inverted. the side with more twists of spring goes down.

12-14-2007, 08:17 PM	#578 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Edmonton, AB Drives: '91 VR4 - RIP Trader Rating: (14)	Re: Lean Misfires at 2700-2800 rpm Thanks for the suggestion. I've been wondering about some sort of valve issue, especially with the ticking noise I get from my rear valve cover. It doesn't really seem to fit 100%, but then again, nothing seems to fit 100%. I suppose maybe an intake valve could be floating/sticking resulting in only 1/2 of the required fuel getting into the cylinder?? __________________ '91 VR4 - Modlist: DR650R turbos, Snow stage 2D alky kit, DSM SMICs, blowthrough ported LT1 MAS, Dejon Tool intakes & y-pipe, Blitz DSBC Spec R, HKS SSQV BOV, PTE 580cc injectors, Dual feed fuel system with Aeromotive FPR & filter, Hotwired Supra pump, HKS DLI, MSD Wires, Apex'i S-AFC II, MAFTranslator, Turbobob ECU, Scanmaster III, LC-1 WBO2, ESP downpipe, Vac/EGR delete, Gutted precats and test pipe, Maximal solid mounts, 300m 18 spline output shaft, Centerforce Dual Friction clutch, RPS flywheel, GC coilover conversions with helper springs, Powerslot slotted rotors, Goodridge SS brake lines, Hawk pads (front), Stillen metal matrix pads (rear)

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12-14-2007, 08:35 PM	#579 (permalink)
badass3000 Wanted: Traction Problems Join Date: Nov 2002 Location: Jacksonville, Fl Drives: 18 Y.O. "badass" VR4 Trader Rating: (20)	Re: Lean Misfires at 2700-2800 rpm if this is an upside-down spring I will eat my sparkplugs, all of them.