If this ain't advanced I don't know what is. Car will not run between 4,000rpm- 5,000rpm. This isn't hard to see like a surge it is very very aparant and heres the proof. http://members.aol.com/rooster433/alvinsmall.jpg OK Before I hear the same solution repeated the following have been tried 1 Autolights 103's 2 NGK TR6's gapped at .025- .045 3 Three different optisparks (2 brand new) 4. New plugs and wires and absoulutely no no arcing (just looked again 30minutes ago) 5. probally 5 different coils 6. MSD coil 7. did this with stock injector positioning/intake and nitrous 8. Two different ignitino box's and does it worse on stock ignition IMPORTANT THING TO NOTE I've had this problem with 100-150hp nitrous shots, and with boost. The problem has also presisted to 2 different motors O2 millivolts are extremely lean but AFR is between 11.0-12.0 on the wideband. This tells me that I have huge misfires (unused oxygen, actually a great way to diagnose bad plug wires on differnet banks) Tomarrow i'm going to try putting a big grounding strap on the motor and see where that gets me. Theres no real reason why that would work but its worth a shot. __________________ 1993 Red Eaton Supercharged Formula 2 Bar stock Speed density PCM 18/26mpg, near 450rwhp Hooker Headers, Flowmaster Muffler, Vigilante 2800 www.PCMFORLESS.com Programing speeddensity.org Video of world's only eaton/roots supercharged LT1

Does your car now have a rising rate fpr ?

FMU.. but you knwo its all right cause the AFR is so steady

If its happenned on two different motors, have you suspected the ECM yet? Also, have you monitored your fuel pressure during the drop in power? Any change?

who cares whta the fuel pressure does.. the AFR stays right

heres a video

http://members.aol.com/rooster433/dyno.mpg

t

Watched the vid. From what it sounds like, it doesent even sound like your losing spark. Beings that its a manual that rules out TCC lockup. And beings you said youve had it with boost OR nitrous, that rules out it being an m112 problem. Did you have the blower on there while the nitrous was used, or was this strictly a nitroused motor? Now when you say two different engines, are you talking shortblock, or complete intake to pan engines?

Because from what your saying, the only thing you havent changed is the ECM, which I suggested earlier. Especially if your o2 is lean but the wideband is saying otherwise.

Its wierd... doesent sound like a misfire or anything like that. All it sounds like is the engine coming under tremendous load, then it being overcame. Its almost like its at the point where the blower is still under vacuum, then suddenly around 4000rpm it reaches enough to form boost, which is bogging down the engine. But as you said if you had the same problem with nitrous, then it cant be the blower.

I'm downloading the video while I'm typing this… maybe seeing it I'll think it's something different…

My thoughts from the description… are you're sure that the a/f ratio doesn't do something funny there? It could be rich or lean, but my instinct is that it's lean enough in that area to cause a misfire which results in extra fuel making it into the exhaust so it's not showing up on your wideband. My second guess would be that your torque peak is right around 4K (peak cylinder pressure) and you're blowing out the spark, but that would really surprise me with a decent ignition and the TR6's at .030" (wouldn't surprise me at all with the autolites).

Looking at the video it makes me think fuel problem even more. Since you can tune your ecm why not just stick bigger injectors in it and removing the FMU, or even just run higher fuel pressure without the FMU? Really, with what you're showing on the graph it should be OK with the stock injectors... Maybe start them at 55psi or so to give you a little extra leeway and go from there. It's not that the fmu is causing the problem but I'm betting that it's making it less intuitive to tune.

Hell, just dump 10-20% more fuel in that range and see what happens

Timing. It's being drastically retarded. The ECM is at fault.

My 85 used to do the same exact thing! It turned out to be a variety of things but all were ESC sensor related, first was the knock sensor was cranked in too tight, secondly my quicky dumps were too close too it so the noise beat upon it under nitrous, third was my fuel quality was too low for my timing. I didn't put it all together until one day when I swithed the tranny and converter to freshen my race one up. I used a stock 700 and converter while I was having the race converter (and tranny) overhauled. the tight converter made it happen without the dump tube open. I figured it out right away, pulled the wire off the sensor and made a run (not recommended) and it went right away. It sounds so clean and so drastic, just like mine did! I cant tell if I am hearing air rushing in the TB or detonation. the sound is so very faint, I suspect that it is the ESC sensor pulling timing and making it fall on its face.

Yeah, I was thinking intake/blower design was the problem but I had the same issue with nitrous. And the nitrous motor was completely different cam/intake/etc. It was so bad with the nitrous I sold it.

It honestly feels like someone hitting a brake on the motor and sometimes you can distinctly hear it breaking up.

It seems like if i thow a rediculus amount of fuel at it it seems to calm down but thats probally just me drowning out the problems. The car is making well over 300rwhp at 3800rpm so running with out a FMU and anything smaller than 42lbs injectors is out.

Also, it did the same thing wih the nitrous/stock injectors. The nitrous was a wet kit.

PROOF OF THE AFR..

http://members.aol.com/rooster433/eaton.mov

This is a Tech Edge wideband, its up the tail pipe but this is the way i've done it for years and its been accurate.

If you look at the tach and listen you can hear its dead spot.

Datamaster is pulling like .5 degrees out, for *** knows what reason.. You can lock the retard ability out of the computer and it still surges but then doesn't set the knock count.

Timing is around 22-23 degrees and can be as low as 17 if the retard is acting up.. To me that sounds reasonable for 9psi non intercooled.

I agree with what has already been said about knock, timing, and fuel.

Here's an off the wall idea. The intake hose is collasping.

he uses a metal one I think

yep its completely steel with a 3.5x10 inch filter

Did you see though? 2 widebands both read the same, and no matter what I do with the timing it still happens.

Really it only does it if i'm using a power adder.

If the Y pipe on this car was extremely crappy would I see results like this?

I dont think so

How about taking the filter off and trying it.

Rob

the air filter is freaking huge, brand new and should be more than enough to satisfy this car.

The last motor did it with a SLP cold air intake too.. I don't see that being the problem

good point

whats a good point?

that it did it with the old intake layout and piping, so that rules out your inlet tube. I have seen that tubing you are using before. If it collapsed it would stay crushed afterwards he thinks your inlet piping is sucking closed but doesnt understand what you are running. and everyone knows a huge K&N type filter wouldnt be the cause.

the only thing consistant between the two motors at this point is the Y-pipe, assembled heads (i inspected the springs a few times), the wiring harness, and computer.

Ignition/intake/blower/poweradder/plugs etc are all different yet the same problem

i'm goin gto go take anthor picture of my Y pipe.. I know that can't be the cause but I can't think of anything else.

OH.. i just put a freaking huge ground on the car too with no help.

It can't be lean either cause i put tons of fuel in the car and all i get is more smoke out the back.

well if it were the springs it wouldnt rev back up after it got past that area of the powerband. so thats a good deal

it seems to me that it could have dog-sh*t for a ignition and still fire at .025

i agree

am i dreaming or is 20 degrees or so of timing plenty for 9psi

the car used to run at 42 (LT1, go figure)

i suppose it could just need more

I understand perfectly what he is running. I didn't when I first asked the question until he answered. The taking off the air filter would eliminate that the filter is collapsing as a cause.

Rob

look at coil wire know to fail

but if he was running a different piping and air filter setup all together before the blower and it did the same thing that would rule it out.

OK, here's another idea. What's your TPS at when this occurs?

Rob

100%

What voltage?

Alot of us have said this and this is my 3rd time... have you tried replacing the ECM? Not trying to be a dick, but that seems like the only part which you havent replaced that could cause the problems your having.

I just don't see the ECM being the problem.
It either works or it doesn't.. it just cna't forget how to work between 4-5 thousand RPM.

The TPS volts don't matter.. this computer records highest value and names it 100%

if your air fuel ratio is right on.id look at ignition, i had the same problem.my car at wot would not go over 5200 rpms.i swapped out old ignition ,problem solved.remember the more pressure in the cylinder the more ignition power u need.

dave

i know.. tried that..

MSD and crane same problem

Youd be VERY surprised what modern electronics can do. I build the stuff all day, and Ive seen some crazy stuff.

I am having same problem. My car lays down at 4000 rpm & sounds like a pack of firecrackers in the intake. If your car runs great without charger belt on you are having a detonation problem. Empty your fuel tank & fill with an unleaded racing gas like 114 octane & then retry with blower belt on. If problem goes away, most likely too much compression or any other reason associated with similar. Hope this helps, it worked for me. I was running 9.8:1 CR, 6lbs boost, cast iron 64cc heads, 7749 sy/ty ecm.

(I was running 9.8:1 CR, 6lbs boost, cast iron 64cc heads,)



That would put you around 13.7:1 Effective Compression. The conversion chart for that is listed here about halfway down the page

I was thinking maybe springs, but you checked it. Just for yahaa's, what is your valvetrain? Any chance it could be a resonance in there?

its had 1.5 and 1.6 roller rockers.. gross lift is under .500 with LT4 hotcam springs.

What is the engine temp when this happens

Yea, I actually started typing exactly that in one of my early responses and deleted it, I can't remember why I decided that wasn't the case. Was it someone on MAFB that had that problem, I can't remember where it was…. FWIW, it's happened before where the springs hit a resonant point and they just loose control of the valves for an rpm band, work fine above and below.

Second, LT4 hot springs? For whatever reason (guessing the LT4's lighter valve train, but I don't think I ever saw an explination that I bought) the springs that come with the LT4 Hot cam kit are actually softer then stock LT1 springs with a lower seat pressure. As far as I know there aren't retainers that are a proper size for them (they were designed to be used with an aluminum retainer that would never live on the street and are odd diameters that don't match any normally available retainers. Used with the stock, LT4 retainers there is noplace for the inner spring to seat, it can be assembled but I wouldn’t trust it to work long). I wouldn't be surprised at all if they were a problem.

300hp too much for stock injectors? The 24lb/hr injectors that came stock on LT1's have been used successfully into the low 400hp range though in theory that should only work if you manage to get a rather low BSFC out of the engine. My orignal point was that you could do it to test if fueling is part of your problem. You may run out of fuel up top then, but you'd also know it if you scanned it durring the run, and that would help narrow things down.

Backfiring in the intake is a dead giveaway that you're lean

I still think that you're going lean in that area causing a misfire which is preventing it from showing up on the O2's. How much boost are you seeing in that range? What ratio FMU are you running?

No doubt it is lean. Why? My theory is the fuel octane is too low causing a rapid uncontrolled burn under boost, in turn letting a whole bunch of oxygen left over to come out the tail pipe. Cause of rapid burn would take too many posts to explore. Lets just assume that is what is happening. The afr in the tail pipe is also reading a "corrected" catalyzied exhaust so keep that in mind while tuning from the tail pipe. A five gas anylizer would show how much oxygen is coming out. Make sure if you have an air pump to "pinch off" the air hoses to stop o2 from entering the exhaust system. In any case, try the fuel, I just destroyed my 700r4 on a hot run last night, car has too much power. The 114 fixed my problem. It took 10 minutes and $20.00 in fuel. If I am wrong you really haven't lost. It is the absolute easiest thing to try. I do plan to lower my CR to 8.5:1 with my new 383 combo.

One more thought, We usually think lean causing misfire. It is possible that misfire looks like lean on o2's & afr, if you don't burn the fuel, you don't use the air, looks like lean, but lean isn't the cause, remember 14 parts air to one part fuel, if you don't use the one part fuel, you still have 14 parts air left over. (14:1 as example only). Misfire is the cause. Just a thought. Try the fuel!