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Bockscar
Joined: 16 Nov 2010
Posts: 392
Location: Sandy, Oregon
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 Posted: Mon Apr 08, 2013 11:31 am Post subject: The 931 engine is a beast |
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Funny thing just happened.
I'm in the process of implementing an EFI solution on my 931 and I've been playing with my wiring setup. I just mounted the ignition modules and coils but I forgot to tighten down the grounds. After about 10 minutes of cranking and the engine only semi-firing, I discovered the problem. Excited, I rushed back to the drivers seat and turned the engine over. Guess what?
BOOOOOOOM
My ears are still ringing. I live in a hilly area and people for miles could probably hear that explosion. Neighbors from all around some crawling out of the woodwork to see what happened. Despite that intensity of the explosion, the engine is still in perfect working order. I was expecting something to have blown out or something, but nope. The engine is built like a tank.
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Brian
'79 924 - Restoration In Progress
'81 924 Turbo w/EFI - Scrapped |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Mon Apr 08, 2013 12:35 pm Post subject: |
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erstwhile owner of just about every 924 variant ever made |
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McGyver
Joined: 24 Feb 2009
Posts: 354
Location: Jelenia Gora - Poland
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| Posted: Mon Apr 08, 2013 12:39 pm Post subject: |
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Maybe that was just shoot in exhaust... but that could destroy turbocharger... you should watch out and don't do this anymore 
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931 82' - 5000km after full engine rebuild
SOLD: 924 81' N/A- with turbo gearbox "dogleg" - great but mysterious car 
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Bockscar
Joined: 16 Nov 2010
Posts: 392
Location: Sandy, Oregon
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| Posted: Mon Apr 08, 2013 12:44 pm Post subject: |
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| McGyver wrote: | | you should watch out and don't do this anymore |
That is a great suggestion, but I am running into a problem.. How? It seems simple, to not have the car backfire when you are dialing in the fuel settings, but since the 931 pistons are dished, if the fuel being injected doesn't get ignited, it's not going anywhere but in that piston dish. The compression won't blow it out' I've learned this the hard way. This proves extremely difficult when trying to figure out just how much fuel the engine needs to start when cold.
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Brian
'79 924 - Restoration In Progress
'81 924 Turbo w/EFI - Scrapped |
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fiat22turbo
Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR
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| Posted: Mon Apr 08, 2013 2:20 pm Post subject: |
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I blew the muffler off the back of my car.
When dialing in cold start settings, start at 1.0 ms and work your way up until it just starts, you keep it running using after start enrichment. This way you get a better sense of the fueling needed without starting too high.
The sucky part is you then take that setting and ambient temperature and you only have one of the several you need. 
Mine is still hard to start, but it is getting better as I tweak it slowly but surely.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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Bockscar
Joined: 16 Nov 2010
Posts: 392
Location: Sandy, Oregon
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| Posted: Tue Apr 09, 2013 1:02 am Post subject: |
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| fiat22turbo wrote: | I blew the muffler off the back of my car.
When dialing in cold start settings, start at 1.0 ms and work your way up until it just starts, you keep it running using after start enrichment. This way you get a better sense of the fueling needed without starting too high.
The sucky part is you then take that setting and ambient temperature and you only have one of the several you need.
Mine is still hard to start, but it is getting better as I tweak it slowly but surely. |
See, if I lived in the woods or back country, I wouldn't worry so much about it, but a live in a nice little town home community and by now, the neighbors know when they hear a car backfire, it's me. Though I don't think anyone was ready for a bomb-like explosion they heard yesterday.
When you say 1.0 ms, do you mean the reqfuel? I have the crank pulse set to 100 (which means the crank pulse isn't any hire than the reqfuel value).
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Brian
'79 924 - Restoration In Progress
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fiat22turbo
Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR
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| Posted: Tue Apr 09, 2013 1:24 am Post subject: |
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No, the pulse width on the Cranking/Priming section in TunerStudio. You are using TunerStudio aren't you?
It might be different between MS1 (which I'm running) and MS2 or MS3
Set the Priming source to "Standard Prime" and then enter 1 in the "Standard Priming PW (mS)" below it and work your way up a tenth at a time. When you get a solid "hit", note the temp and put that in a notepad to start building a table, you could probably "scale" the table from these results and then fine tune them later.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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Bockscar
Joined: 16 Nov 2010
Posts: 392
Location: Sandy, Oregon
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| Posted: Tue Apr 09, 2013 1:30 am Post subject: |
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| fiat22turbo wrote: | No, the pulse width on the Cranking/Priming section in TunerStudio. You are using TunerStudio aren't you?
It might be different between MS1 (which I'm running) and MS2 or MS3
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I'm using TunerStudio with MSExtra and MS2. I have my priming pulse off entirely, because I've read that constantly turning the key on and off can allow the priming pulse to flood it. I have my Crank Pulse set to 100% of ReqFuel (The stock value was 240% of reqfuel).
For what it's worth, the engine doesn't have much problem actually cranking, it's the warm up enrichment that causes problems. That's another issue entirely though.
For the record, I've noticed that increasing the fuel pressure allows a substantially greater amount of fuel to be injected with each pulse. What is your fuel pressure? Perhaps mine is too high and too much fuel is being injected when the injectors open.
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Brian
'79 924 - Restoration In Progress
'81 924 Turbo w/EFI - Scrapped |
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fiat22turbo
Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR
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| Posted: Tue Apr 09, 2013 1:49 am Post subject: |
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I'm using 33pph injectors at 55psi with the vacuum port disconnected.
With the ITB's I'm not pulling nearly as much vacuum at idle as you would (about 70-76kpa) so my pressure at idle is higher than they would be on a car running a single TB and a manifold with a plenum.
Changing the base fuel pressure will impact the amount of fuel delivered across the range at the potential expense of the total volume of fuel the pump is capable of delivering. Its a balancing act, but keep it simple and set the pressure to something reasonable between 40-60psi at ambient air pressure and leave it until you get it more well tuned. The regulator will need to be boost referenced to increase the fuel pressure while under boost to keep the fuel pressure high enough to overcome the pressure in the intake tract and inject the fuel properly.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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Bockscar
Joined: 16 Nov 2010
Posts: 392
Location: Sandy, Oregon
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| Posted: Tue Apr 09, 2013 2:00 am Post subject: |
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| fiat22turbo wrote: | I'm using 33pph injectors at 55psi with the vacuum port disconnected.
With the ITB's I'm not pulling nearly as much vacuum at idle as you would (about 70-76kpa) so my pressure at idle is higher than they would be on a car running a single TB and a manifold with a plenum.
Changing the base fuel pressure will impact the amount of fuel delivered across the range at the potential expense of the total volume of fuel the pump is capable of delivering. Its a balancing act, but keep it simple and set the pressure to something reasonable between 40-60psi at ambient air pressure and leave it until you get it more well tuned. The regulator will need to be boost referenced to increase the fuel pressure while under boost to keep the fuel pressure high enough to overcome the pressure in the intake tract and inject the fuel properly. |
Interesting, ok. I am running 42lbs injectors at 60lbs fuel pressure with the vacuum hose unplugged. I'm not sure how MS1 handles pulse width modulation but, there is no PWM with MicroSquirt; either the injectors are open or they are closed.
I'm going off of memory here but, if I recall when cranking, all of the injectors open for 3.x milliseconds (all 4 injectors, because its crank mode). Now, 3.x milliseconds @ 60lbs of fuel pressure allows far more fuel than 40lbs of pressure. Perhaps that is my problem. I realize that I am using far heavier duty injectors than I should be using. These are them:
http://www.turnermotorsport.com/p-2021-bosch-42lb-fuel-injector-green-top-bosch-0-280-155-968.aspx
Here's a quote: "...you must have specialized tuning, as these provide far too much fuel with a stock or naturally aspirated setup." ..Maybe I went a little overboard when i bought these....
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Brian
'79 924 - Restoration In Progress
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Grenadiers
Joined: 20 Feb 2007
Posts: 3222
Location: Nelson, WI & Prescott, AZ
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| Posted: Tue Apr 09, 2013 6:56 am Post subject: |
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I have SRT-4 injectors, 570cc! Even with a weak engine, mine starts and runs fine, using 59psi for fuel. Having a problem with an incorrectly wired IAC since day one, so i have to be patient on the warmup sequence. The ReqFuel is 2.9ms.
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Bockscar
Joined: 16 Nov 2010
Posts: 392
Location: Sandy, Oregon
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| Posted: Tue Apr 09, 2013 7:34 am Post subject: |
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| Grenadiers wrote: | | I have SRT-4 injectors, 570cc! Even with a weak engine, mine starts and runs fine, using 59psi for fuel. Having a problem with an incorrectly wired IAC since day one, so i have to be patient on the warmup sequence. The ReqFuel is 2.9ms. |
WOW! that is incredible. Was the ReqFuel value generated for you by TunerStudio or did you figure it out yourself? I am wondering if my ReqFuel value is too high. It is set at 7.6 by TunerStudio.
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Brian
'79 924 - Restoration In Progress
'81 924 Turbo w/EFI - Scrapped |
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Grenadiers
Joined: 20 Feb 2007
Posts: 3222
Location: Nelson, WI & Prescott, AZ
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| Posted: Tue Apr 09, 2013 8:07 am Post subject: |
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Using 'Simultaneous' and 2-squirts per cylinder, which currently has worked best for me, I have 5.9 which gets divided by 2. Once I get the engine rebuilt, I'm sure this will probably change as I tune a healthy engine.
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'83 944 Track car.
'88 924S Track car.
'89 944 Turbo
2004 Winnebago Vectra monster RV
2012 Jeep Wrangler
2014 Kia Soul
2001 Ford F350 powerstroke |
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924 FAQ (Technical)
