Lean Misfires at 2700-2800 rpm - Page 18 - 3000GT/Stealth International Message Center

DoctorDex · 03-11-2007, 09:24 PM

I took my car out of storage today and after installing my newly refurbished ECU, I took the car out to make some logs.

After making some logs, I am now of the opinion that I have/had two different problems. I no longer have any misfires per say. When I say that, I mean I no longer have knock and/or popping exhaust while cruising between 2000 - 3000 rpm and my AFR isn't jumping up to 16.8 anymore.

However, what I do have is a serious issue with pressure pulsing. At cruise in 5th gear (or even 4th), between 2000 - 3000 rpm, if I accelerate and then slowly ease off the throttle partway, my bov will start blowing off (ie. psh psh psh psh) and it will just continue until I finally let off the throttle completely. If at that point, I step on the throttle again there is no issue. It only happens if I ease off the throttle part way. While its pulsing my AFR bounces between 14.8 and 14.1 and my O2 trim bounces between 90 - 140.

I will post some logs tomorrow.

badass3000 · 03-12-2007, 09:28 AM

Quote:

Originally Posted by DoctorDex

my bov will start blowing off (ie. psh psh psh psh) and it will just continue until I finally let off the throttle completely.

might not be your BOV!?!

DoctorDex · 03-12-2007, 03:59 PM

Why would it be my bov? I'm using a HKS SSQV and it is supposed to be one of the most sensitive BOVs out there. At one point in time, because of this exact same problem, I modified the bov, by adding an extra nipple, to make it more sensitive. However, because I'm running blow through, I believe there was too much turbulence created by the open bov @ idle. Therefore, I ended up having to cap the extra nipple. I have a feeling the only way I'm going to get a rid of this problem is if I switch to a MAP system or back to a draw through...

davidm5287 · 03-13-2007, 12:53 PM

I too am still having this problem, but the weather has been getting warmer and I am finding the problem is becoming less noticeable and its starting to smooth out. What do you think this could relate to?

badass3000 · 03-13-2007, 01:40 PM

the reason I say that is b/c I have been there, I then removed my BOV and put it in the back seat and still heard the noise

DoctorDex · 03-13-2007, 05:06 PM

So what you're saying is you still had pressure pulsing even without running a BOV whatsoever? What kind of intercooler setup do you have? Whats your piping like?

I have crap piping going to and from my DSM SMICs. The guy who did mine added some "piping extensions" which are bigger than needed. The piping goes from 1.5" to 2" and then back to 1.5". I suspect this is probably adding to my pressure pulsing problem.

I have to admit, I still can't decide whether this problem is related to a lean spot in the fuel map or if its related to pressure pulsing. In 5th gear on the highway I can hear a the bov rhythmically blowing off, however, in 1st and 2nd I can feel a pulse/misfire but I can't hear any air blowing off.

Here is a log, as promised, of the pressure pulsing @ highway cruise. Hopefully by the end of the week I'll have a map sensor rigged up to record any pressure changes in the y-pipe vs. the plenum.

badass3000 · 03-13-2007, 06:20 PM

Quote:

Originally Posted by DoctorDex

So what you're saying is you still had pressure pulsing even without running a BOV whatsoever? What kind of intercooler setup do you have? Whats your piping like?
...

Yes, chuff chuff w/o a BOV!

FMIC=Custom coach, you know the typical two 2" pipes going to the IC then a huge 3" going to the TB.

I am very confedent I DID NOT have this 2800rpm shit when I noticed the pressure pulsing, this is something relitivly new. It feels almost like firing on 5 cylinders till 3000rpm then fires on all 6.

I wonder if low compression in one cylinder could be the culprit? Hows your compression numbers?

I have a new engine that I have been waiting to install untill I had this figured out. Perhaps installing the new engine would solve it?

DoctorDex · 03-13-2007, 09:12 PM

I agree with your description that it feels like 5 cylinders til 3000rpm and then 6 cylinders thereafter. Try upping your base timing, that way you can get more power from your 5 cylinders until the 6th one kicks in.

Running a base timing of 7.5 degrees has made this problem a bit more tolerable.

With regards to a new engine, I don't have the time/money to do a fresh build up, so I hope it doesn't take a new engine to solve this problem As far as compression is concerned, the last time I checked (mid last summer) my compression was fine. If my memory serves me correctly I believe all six cylinders were between 149-153psi. I'm planning on checking it again sometime in the next few weeks and I'll post numbers at that time.

Oh yeah by the way, I took a look at my TPS voltages and there was a smooth transition from closed to WOT. So I guess that rules out TPS.

davidm5287 · 03-14-2007, 06:37 AM

I have the same problem you are describing and I have a freshly rebuilt motor so that rules that out as well.

DoctorDex · 03-14-2007, 07:20 PM

We had a freak storm here today and it dropped to like -17 degrees Celsius (1 fahrenheit). This is the first time I've driven my car in such cold conditions.

I took my car out for a spin and I noticed the missing/pulsing/5 cylinder feeling was much more noticeable with the cold weather. In 1st gear its pretty mild, but in 2nd it was very pronounced and when it missed, I could hear my bov blow off (or whatever is making the chuff chuff sound). 3rd gear was much the same as 2nd. This leads me to think it is a pressure pulsing problem. However, I'll go for a drive tomorrow with my y-pipe disconnected just to be sure.

03-11-2007, 09:24 PM	#171 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Edmonton, AB Drives: '91 VR4 - RIP Trader Rating: (13)	Re: Lean Misfires at 2700-2800 rpm I took my car out of storage today and after installing my newly refurbished ECU, I took the car out to make some logs. After making some logs, I am now of the opinion that I have/had two different problems. I no longer have any misfires per say. When I say that, I mean I no longer have knock and/or popping exhaust while cruising between 2000 - 3000 rpm and my AFR isn't jumping up to 16.8 anymore. However, what I do have is a serious issue with pressure pulsing. At cruise in 5th gear (or even 4th), between 2000 - 3000 rpm, if I accelerate and then slowly ease off the throttle partway, my bov will start blowing off (ie. psh psh psh psh) and it will just continue until I finally let off the throttle completely. If at that point, I step on the throttle again there is no issue. It only happens if I ease off the throttle part way. While its pulsing my AFR bounces between 14.8 and 14.1 and my O2 trim bounces between 90 - 140. I will post some logs tomorrow. __________________ '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)

03-12-2007, 03:59 PM	#173 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Edmonton, AB Drives: '91 VR4 - RIP Trader Rating: (13)	Re: Lean Misfires at 2700-2800 rpm Why would it be my bov? I'm using a HKS SSQV and it is supposed to be one of the most sensitive BOVs out there. At one point in time, because of this exact same problem, I modified the bov, by adding an extra nipple, to make it more sensitive. However, because I'm running blow through, I believe there was too much turbulence created by the open bov @ idle. Therefore, I ended up having to cap the extra nipple. I have a feeling the only way I'm going to get a rid of this problem is if I switch to a MAP system or back to a draw through...

03-13-2007, 12:53 PM	#174 (permalink)
davidm5287 Forum Member Join Date: May 2005 Location: Massachusetts Drives: 92 Stealth TT Trader Rating: (4)	Re: Lean Misfires at 2700-2800 rpm I too am still having this problem, but the weather has been getting warmer and I am finding the problem is becoming less noticeable and its starting to smooth out. What do you think this could relate to?

03-13-2007, 01:40 PM	#175 (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 the reason I say that is b/c I have been there, I then removed my BOV and put it in the back seat and still heard the noise

03-13-2007, 09:12 PM	#178 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Edmonton, AB Drives: '91 VR4 - RIP Trader Rating: (13)	Re: Lean Misfires at 2700-2800 rpm I agree with your description that it feels like 5 cylinders til 3000rpm and then 6 cylinders thereafter. Try upping your base timing, that way you can get more power from your 5 cylinders until the 6th one kicks in. Running a base timing of 7.5 degrees has made this problem a bit more tolerable. With regards to a new engine, I don't have the time/money to do a fresh build up, so I hope it doesn't take a new engine to solve this problem As far as compression is concerned, the last time I checked (mid last summer) my compression was fine. If my memory serves me correctly I believe all six cylinders were between 149-153psi. I'm planning on checking it again sometime in the next few weeks and I'll post numbers at that time. Oh yeah by the way, I took a look at my TPS voltages and there was a smooth transition from closed to WOT. So I guess that rules out TPS.

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03-14-2007, 06:37 AM	#179 (permalink)
davidm5287 Forum Member Join Date: May 2005 Location: Massachusetts Drives: 92 Stealth TT Trader Rating: (4)	Re: Lean Misfires at 2700-2800 rpm I have the same problem you are describing and I have a freshly rebuilt motor so that rules that out as well.

03-14-2007, 07:20 PM	#180 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Edmonton, AB Drives: '91 VR4 - RIP Trader Rating: (13)	Re: Lean Misfires at 2700-2800 rpm We had a freak storm here today and it dropped to like -17 degrees Celsius (1 fahrenheit). This is the first time I've driven my car in such cold conditions. I took my car out for a spin and I noticed the missing/pulsing/5 cylinder feeling was much more noticeable with the cold weather. In 1st gear its pretty mild, but in 2nd it was very pronounced and when it missed, I could hear my bov blow off (or whatever is making the chuff chuff sound). 3rd gear was much the same as 2nd. This leads me to think it is a pressure pulsing problem. However, I'll go for a drive tomorrow with my y-pipe disconnected just to be sure.