home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > performance & modifications

Reply
 
Thread Tools Display Modes
Old 02-19-2021, 06:01 AM   #1
maxitoman007
Board Member
 
maxitoman007's Avatar
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
Default Backfire under boost [VIDEO] Retarded timing?

So recently my modified 87 740 turbo began doing this under boost. It happens more so at higher loads (which is almost all the time because my volvo is lifted on 33s) however I can rarely even get a 1st gear (CD009) pull without some backfiring. It is worse at WOT as opposed to trying to build boost at moderate throttle.

Up until today I had several cracks in my stainless turbo manifold and I thought those could be causing the issue. I had those all TIGed up today and on the drive home it was still happening.

Here is a video for reference. This was in third gear (CD009) trying to build boost around WOT tonight after the manifold had been repaired:

https://imgur.com/gallery/Vvw0xJK

I am trying to figure out what could be causing this issue. Have any of you seen anything like this before?

knock sensor pulling timing? (I recently installed an MSD 6a box which actually seemed to change the tone of the engine sound, possibly tripping the knock sensor?)
bad MAF?
Bad base Timing?
Too rich?
should I try retarding cam timing? (I have an IPD turbo cam with adjustable cam gear set straight up)

Thanks in advance.
maxitoman007 is offline   Reply With Quote
Old 02-19-2021, 07:31 AM   #2
KwikBrik245
Board Member
 
KwikBrik245's Avatar
 
Join Date: Oct 2008
Location: Cleveland, OH
Default

If you are still running LH, I believe there is a switch under the dash by your pedals that takes away fun when it sees too much boost.
__________________
Daily: '91 245, B230F/M46 P-type, '93 Dana 30

'88 744, Twin Turbo LS1/T56, Grizzly locked Dana 30.
KwikBrik245 is offline   Reply With Quote
Old 02-19-2021, 07:41 AM   #3
KwikBrik245
Board Member
 
KwikBrik245's Avatar
 
Join Date: Oct 2008
Location: Cleveland, OH
Default

This guy
Attached Images
File Type: png Screenshot 2021-02-19 064015.png (104.9 KB, 92 views)
KwikBrik245 is offline   Reply With Quote
Old 02-19-2021, 10:19 AM   #4
maxitoman007
Board Member
 
maxitoman007's Avatar
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
Default

Quote:
Originally Posted by KwikBrik245 View Post
If you are still running LH, I believe there is a switch under the dash by your pedals that takes away fun when it sees too much boost.
Thanks for the reply. The overboost switch has been long disabled on this car so I don’t think that’s what’s causing it. Good idea though.

Does the overboost switch pull timing? I’m still just trying to figure out what I’m even seeing, pulled timing, misfire, etc.
maxitoman007 is offline   Reply With Quote
Old 02-19-2021, 10:59 AM   #5
vwbusman66
Stößelstange über alles
 
vwbusman66's Avatar
 
Join Date: Oct 2016
Location: Kingsville, MD/ Morgantown, WV
Default

Based on the wideband in the video, it's going pig rich (like 10.1:1) as soon as it starts backfiring.
I'm wondering if your spark isn't very strong and is blowing out as soon as you start to see elevated cylinder pressures, dumping unburned fuel out of the turbo.

Makes for a sick faux rolling anti-lag though.
__________________
1971 142 beater
Quote:
Originally Posted by linuxman51 View Post
the only problem with that is what you define as cheap and fast
Quote:
Originally Posted by propav8r
The incest is implied.
vwbusman66 is offline   Reply With Quote
Old 02-19-2021, 11:02 AM   #6
VB242
Beep beep zip tang
 
VB242's Avatar
 
Join Date: Sep 2011
Location: The Right Coast
Default

I was having some missing and backfiring, the fuel injector inlet screens were getting clogged with very fine rust from the tank, so it kept running lean and I kept dialing up the fuel so that the injectors that were less clogged were running rich. Got my injectors cleaned and it fixed the problem.
__________________
Quote:
Originally Posted by 240240 View Post
I'm shocked someone actually took me seriously.
VB242 is online now   Reply With Quote
Old 02-19-2021, 11:15 AM   #7
Janspeed
Board Member
 
Join Date: Sep 2005
Default

Spark blowout?
Check the overall condition of the plugs: worn electrodes? Any cracks in the porcelin? Any dirt or carbon build-up in the recesses of the plugs?
Check the plug gaps. Try closing them up to about 0.6mm (ignition is slightly harder when the mixture is under boost pressure)
Check the cap + rotor: any (often greenish) corrosion? Any hairline crack in the cap?
Are all wires OK? (you could test them by spraying a fine water mist on them while the engine is running, when it is dark outside you might see sparks jump from a faulty wire) Do they make good contact?

In short: make sure that the ignition system is 100% perfect.
Janspeed is offline   Reply With Quote
Old 02-19-2021, 12:27 PM   #8
rb92673
Board Member
 
Join Date: Jan 2017
Location: San Clemente
Default

Mine was doing similar. I had a burnt exhaust valve. It was pushing un-burnt fuel into the exhaust manifold where it would ignite. Made for great turbo spin up, 20 psi at 4500 rpm.

http://forums.turbobricks.com/showthread.php?t=352563
rb92673 is offline   Reply With Quote
Old 02-19-2021, 01:11 PM   #9
142 guy
Board Member
 
Join Date: May 2014
Location: Saskatchewan, Canada
Default

Do you have a blow off valve venting to atmosphere? If not, where is the flame coming from if the exhaust manifold was repaired?

If you have an atmospheric venting blow off valve, the upset in your AFRs would be normal because the MAF is no longer accurately metering flow and tends to cause the AFR to go low. The question for me is that if this is a back fire, why is the BOV opening. The BOV would normally open to maintain compressor flow when the throttle closes giving high pressure before the throttle and low pressure in the manifold. If this were a back fire I would expect high pressure in both the intake manifold and pre throttle (assuming the throttle is wide open) which should not operate the BOV.

Normally, in order to get back fire which causes ignited mix to flow back into the intake system you have to have seriously advanced ignition timing (lighting off the charge mix before the intake valve is closed) of some kind of selective pre ignition problem. Seriously out of whack valve timing resulting in the intake valve being open when normal ignition occurs will also cause that; but, that problem would be present all the time because of the fixed valve timing on the B230FT.
142 guy is offline   Reply With Quote
Old 02-19-2021, 08:21 PM   #10
bobxyz
Board Member
 
bobxyz's Avatar
 
Join Date: Aug 2014
Location: Boulder CO
Default

That sure looks like antilag-like behavior (youtube: "turbo antilag", but don't get sucked in...).

Anti-lag is a way of keeping the turbo spooled up while shifting, or waiting to launch. Instead of burning all the fuel in the cylinder with the valves closed, antilag gets unburnt fuel into the exhaust and then ignites it. The energy then goes into spinning up the turbo, instead of the engine's power stroke.

You're looking for something that both gets unburnt fuel into the exhaust, and something to ignite it. I'm not sure if heat alone is normally enough to ignite the exhaust gases.

For race ECMs, anti-lag is often setup as late ignition timing and extra fuel. The late ignition timing results in the fuel still burning when the exhaust valve opens, which ignites whatever extra fuel is already in the exhaust. To get unburnt fuel into the exhaust, the ECM can be setup to do a cyclic spark cut, meaning no spark every so often for each cyl. For example, the MegaSquirt3 anti-lag description is here: http://www.msextra.com/doc/pdf/html/...p-1.5-114.html

If you can, I'd try swapping back to the standard ignition, instead of MSD, and see if the behavior changes. Next would be a compression check, just to rule out any head gasket or valve issues. If those are good, you could try adjusting the fueling and spark advance by a little bit to see if the behavior changes. Or, maybe someone here with LH2.2 experience will recognize the issue.
bobxyz is offline   Reply With Quote
Old 02-19-2021, 09:38 PM   #11
2turbotoys
Salaminizer
 
2turbotoys's Avatar
 
Join Date: Nov 2007
Location: Reading pa
Default

One cheap thing to try is side gap the spark plugs if it is spark blowout, but as bobxyz said it is kinda acting like antilag. Meaning ignition timing is way off for whatever reason. That could explain why your exhaust manifold is cracked, antilag is very hard on manifolds.
__________________
Feedback thread https://forums.tbforums.com/showthread.php?t=144924

1978 242, 5.3 L33
1979 242, MS, R brakes
2006 V50 T5 AWD @ 17 PSI
2turbotoys is offline   Reply With Quote
Old 02-20-2021, 11:24 AM   #12
Dirty Rick
Board Member
 
Dirty Rick's Avatar
 
Join Date: Apr 2013
Location: Cornholio, OR
Default

I saw 10:1 on the afr before the missfire, I don't think you are making enough boost to go that rich.
__________________
I don't know who I am when I am somebody else.
Dirty Rick is offline   Reply With Quote
Old 02-20-2021, 12:37 PM   #13
142 guy
Board Member
 
Join Date: May 2014
Location: Saskatchewan, Canada
Default

Begs the question, is the OP incurring back fire which is combustion products exiting through the intake system (the always spectacular flame exiting the chokes on a 4 barrel carb followed by ignition of the fuel in the float bowls and subsequent immolation) or after fire where combustion is occurring completely or partly in the exhaust system. True back fire is pretty rare and frequently fatal for the engine (particularly for positive displacement superchargers without a pressure relief). After fire is not so uncommon and can range from the popping sound from the exhaust due to trailing throttle over run to cherry red exhaust manifold associated with grossly retarded ignition or grossly low AFRs. After fire would be consistent with damage to the exhaust manifold

If it is after fire, I would be looking for upsets in the ignition timing or fuel mixture first. After that its a mechanical problem; but on a B230 FT if it was a mechanical problem I would expect the after fire problem to be present just about all the time.
142 guy is offline   Reply With Quote
Old 02-21-2021, 02:15 PM   #14
maxitoman007
Board Member
 
maxitoman007's Avatar
 
Join Date: Feb 2017
Location: Calgary, Alberta, Canada
Default

I seemed to have fixed the issue. I first replaced my distributor with a spare I had laying around which I cleaned before install. I also replaced my NGK BR7ES spark plugs gapped to 0.28" to NGK BPR7ES plugs gapped to 0.025". Problem gone (so far).

It seems the issue was spark blowout. Thanks everybody for the suggestions.

One of my buddies also turned the boost controller all the way down hence why it was so rich under boost. Normally I'm running much higher boost levels.

Now its time to deal with the new manifold cracks from the 2-step and my newly snapped axle shaft... woohoo!
maxitoman007 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 10:24 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.