swlabhot

I'm a firm supporter/user of this as far as non-standalone is concerned as it has been working very well for my setup for about year and a half now and I've done several track days in it successfully.

Anyway to get to the point, I had an eventfull unfortunate weekend My B18C6 engine blew as I was overtaling a car on the freeway Its been running strong on 10psi with no issues at all, but I got greedy and thought I'll crank up my DIY manual boost controller a little to see how much psi I can get out of the stock MAP in my setup. I also wanted to confirm the AFC hack Recurve theory.I thought that that it would be pretty safe as I guessed that I'm pretty much on the limit of the stock MAP and the WORST that could happen is it could spkie to about 1bar in my setup and I would get a CEL stopping me from going further... To my horror my boost gauge was seeing 18psi+ .....No CEL, No fuel cut it just kept on climbing! So I quickly backed off quickly and thought I was seeing things or the gauge started to act funny. Later that day I tried it again to see if it corresponds to my VAFC vac readout and at about 18psi again, the AFC was showing about 0.75 which is around 10.5psi ?!?! <confused> so I gave the AFC the benifit of the doubt over the boost gauge and carried on boosting 1 more time and next thing I know the whole freeway was a smoke screen.....it gave up the ghost The engine stalled and would not start again. I'm not sure what damage has been done yet as they haven't dismantled the block yet but a quick initial diagnosis seems to be the head gasket....

How could this possibly happen? I'm puzzled why it didn't hit the MAP limit and cause it to CEL. The fuel trim is around -45% plus/minus 3-4% on stock fuel pressure and 500cc injectors.

Please share your thoughts.

racinskittle

Man, that's the stupidest **** ever. Why would you waste an engine like that?!

swlabhot

Please provide some USEFUL constructive feedback and keep this forum technical. I don't need any lectures or people telling me what I should and shouldn't do with my car.

RobbieG35

I don't think I would take a chance on nuking my motor just to see how much the MAP can hold

My friend was boosting 14lbs on an AFC hack and stock MAP - Never had a CEL once. Ended up blowing up of course - I am curious too

notoriousB

I'm running the hack also (for now) and my MBC spikes to 12 psi sometimes w/ no CEL and no problems running.

Can't wait to get my AEM EMS installed, tho I'm somewhat scared of tuning it...

USDM 4G VTEC

remember the stock MAP sensor can only read 1.75 BAR of absolute pressure

means the MAP wont read anything over the 10.8 PSI... and since it cant read anything over that, thats why the VAFC stopped at .75 BAR

i have had this happened to me before, and i went accidentally to 20psi.... but i did threw a CEL
i dont think u threw a rod, but i do think u have melted a piston

time for a rebuilt with forged internals, and a new Map sensor

swlabhot

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by USDM 4G VTEC &raquo;</TD></TR><TR><TD CLASS="quote">remember the stock MAP sensor can only read 1.75 BAR of absolute pressure

means the MAP wont read anything over the 10.8 PSI... and since it cant read anything over that, thats why the VAFC stopped at .75 BAR

i have had this happened to me before, and i went accidentally to 20psi.... but i did threw a CEL
i dont think u threw a rod, but i do think u have melted a piston

time for a rebuilt with forged internals, and a new Map sensor </TD></TR></TABLE>

Yeah I've also been thinking about the possiblity of the VAFC not reading anything above the stock map. I guess your theory makes sense since the boost guage reads the vacuum directly off the intake mani, it is able to read boost up to the limit on the gauge itself.

I think the rods should be OK and most likely the pistons could be fried but I'm praying and being optimistic that I can get away with just a blown HG.... Pretty unlikely though. The internals are built and has only done about 2.5k miles Looks like it would have to be rebuilt yet again...

Muckman

iTrader: (2)

I thought the VAFC manipulated the MAP sensor voltage input into the ECU, meaning it hides the true value. ?

raene

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Muckman &raquo;</TD></TR><TR><TD CLASS="quote">I thought the VAFC manipulated the MAP sensor voltage input into the ECU, meaning it hides the true value. ?</TD></TR></TABLE>

That is true, and that's why the stock map limiter never kicked in. The AFC never read a voltage that would correspond to an ECU input of greater than 0psi manifold pressure. Say it read 10lbs of boost in the manifold and that converted to 2"/Hg after a -35% correction factor... well, the MAP sensor can only read up to 10lbs, so if you pack 40lbs into the manifold, the AFC will still be reading the sensor's maximum of 10 lbs, and still be feeding the ECU 2"/Hg. Turn it up to 60 lbs and the map will still only read its maximum, and the AFC will only correct that maximum.

It's not magical, it's a hack, and it's limited by the stock equipment as well. swlabhot, too bad for your engine, shoulda read a little more about the hack before trying your luck like that It's an expensive mistake to make.

You won't be able to run a MAP sensor other than stock without switching engine management, FYI.

beepy

That all makes sense, but:

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">My B18C6 engine blew as I was overta[k]ing a car on the freeway</TD></TR></TABLE>

I have always had problems with passing on the freeway with the hack. My SAFC, at least, is tuned perfectly for how the turbo behaves when boosting from a standing start. The problem is that boost is not RPM-dependant, and when I try to boost on the freeway, I will make full boost the moment I mash the thottle... Usually at a lower RPM than the AFC is expecting full boost. This always leads to a lean condition, and may be the major factor in what happened to your motor.

(I am still working on the circuit to correct the problem and make the SAFC boost-dependant)

boosted-delslow

Dont you have a a/f guage in your car!?!?

pollito

If you use the AFC with a missing link, then yes you would tune it via RPM only. We are talking about the hack. The hack will add fuel depending on Pressure, not only just rpm.

mattssi

Basically to put it simply. Your motor quit on you because your stock map couldn't read the 18 psi that your were pushing. So you ran lean, and more than likely melted a piston. If you stayed within the confines of what your stock map could read, then you might have been safe.
You should have fixed your problem after it went to 18 psi the first time. Too bad though, probably was a nice motor.

notoriousB

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by pollito &raquo;</TD></TR><TR><TD CLASS="quote">The hack will add fuel depending on Pressure, not only just rpm.</TD></TR></TABLE>

It will, but you can only adjust fuel vs. RPM - you can not "tune" the hack to provide fueling under different engine loads, only at different RPM points independent of pressure.

Joseph Davis

To sum up:

Stock MAP sensor reads max of 10.4-10.8 psi. If you run 10 psi, it reads 10 psi. If you run 11 psi, it reads ~10.8 psi. If you run 18 psi, it reads ~10.8 psi.

ECU freaks out at any pressures over atmospheric, which is recognizes as 3-3.1 volts MAP sensor input. When you stick an AFC in line and lower the MAP input you can let the ECU "see boost" - no, not really, but that's the end result. So you had your AFC taking out enough MAP sensr voltage that when the MAP maxed out at ~10.8 psi, it wasn't sending back more than an atmospheric pressure ~3.0 volt reading.

Bye bye B18C6...

swlabhot

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by raene &raquo;</TD></TR><TR><TD CLASS="quote">You won't be able to run a MAP sensor other than stock without switching engine management, FYI. </TD></TR></TABLE>

Yes I know. I already have a GM 3bar map 880cc and P28 with Uberdata sitting here for ages. If I didn't have problems in getting Uberdata to run, it would have been in there by now. As I kept getting CEL codes 20 and 22 no matter what options I turned on or off in UD, I'm having to hold out until I get the P28 checked out.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by beepy &raquo;</TD></TR><TR><TD CLASS="quote">That all makes sense, but:
I have always had problems with passing on the freeway with the hack. My SAFC, at least, is tuned perfectly for how the turbo behaves when boosting from a standing start. The problem is that boost is not RPM-dependant, and when I try to boost on the freeway, I will make full boost the moment I mash the thottle... Usually at a lower RPM than the AFC is expecting full boost. This always leads to a lean condition, and may be the major factor in what happened to your motor.

(I am still working on the circuit to correct the problem and make the SAFC boost-dependant)</TD></TR></TABLE>

It may well have been a lean condition but I was thinking had more to do with timing. -4 deg static at 10psi is OK but 18psi.....is another story. Tho I had my wideband display in the car, my eyes was fixed on the boost gauges as I was curious as to why it went up so high. I bet it would have easily went over 20psi if it had kept going. I wish I was datalogging at the time so I know how lean I was, if I was lean. It was street tuned at around 12 afr up to redline with my WB.

I think I cracked a sleeve but the rest survived from my mechanics voicemail (I couldn't quite hear him well enough). Guess I'll find out tomorrow for sure when I talk to him.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by J. Davis &raquo;</TD></TR><TR><TD CLASS="quote">To sum up:

Stock MAP sensor reads max of 10.4-10.8 psi. If you run 10 psi, it reads 10 psi. If you run 11 psi, it reads ~10.8 psi. If you run 18 psi, it reads ~10.8 psi.

ECU freaks out at any pressures over atmospheric, which is recognizes as 3-3.1 volts MAP sensor input. When you stick an AFC in line and lower the MAP input you can let the ECU "see boost" - no, not really, but that's the end result. So you had your AFC taking out enough MAP sensr voltage that when the MAP maxed out at ~10.8 psi, it wasn't sending back more than an atmospheric pressure ~3.0 volt reading.

Bye bye B18C6...

</TD></TR></TABLE>

Yeah I guess this makes sense now. Oh well, we live and learn... You just don't think that it will happen to you until it does. Guess I was pushing my luck. Thing is I trash it hard and it was running so strong I just didn't think it could let go so easily even tho my conscience tells me how easily I could overstep the mark. Such is the dark side...

Still I guess it could be time to move on to the next best thing - 3.2l NSX Every downside has an upside

BoostR41

if the map code goes you can still drive at full throttle with and just be rich....at part throttle is a different story