Insane detonation after LA3 swap

[StangBoy]

you mentioned it does it in all gears now?
distributor hold down is tight?
small or large VAM?


I ran a stock 87 NA mustang motor with a t3, volvo front mount and an LB3 with 10psi and even in premium mode with timing at around 6-8* btdc i could make it through first, launching off the rev limiter even with 8psi all the way into 4th and just as boost would hit it would detonate. i had an svo top mount on it and would have to let off in the middle of third because of detonation. even if you had an NA head on it it shouldnt detonate like this.



btw, i rattled this motor pretty hard a couple times with no knock sensor and its still in perfect shape and it getting a fully ported turbo head and ported intake to prepare it for 15+ psi. cast pistons FTW

[litdog]

It only goes crazy in second or first if it's really hot outside. Holddown is tight, large vam. I'll just worry about getting the fuel pressure right and upgrading the fuel system before I worry about getting into this too far. Better to know everything else is right before I get too greedy with power.

[NavySVO]

I removed the vacuum line and went for a drive, figuring the 47psi fuel pressure minus the 8psi of boost would be close to where it should be set stock... It made no difference at all in the detonation.

I am curious as to why you would do this. If anything were to happen, you would end up detonating more.....

I would get it to a dyno with A/F ratio capabilities.

My book shows that code 54 is vane air flow sensor out of range.

Mike, my resources show 54 as ACT or VAT sensor fault, circuit open. If this is true, then that would explain the detonation.

Lit, test your VAF meter VAT sensor. There is a procedure here on how to do it. Also, see if you can borrow another gage to re-test the fuel pressure just to make sure it's actually 47 psi. That's a lot cheaper than a new FPR.

[SVOeric]

That's high with the vacuum line off, not on.

I checked all the voltages on the vam, they checked out for everything I've read on it...

You missed my point completly --

For ever psi of boost, you should be gaining 1 psi of fuel pressure (which is why it's a bad idea to take the vacume hose off the FPR)-- also as load increases, so does fuel demand, so when you drive down the road, and romp on it, the fuel pressure may be dropping, instead of increasing.

which is why you need to run a fuel pressure gauge out the hood, and tape it down to the windshield, and drive it down the street.

After a run, pop the hood, see if the exhaust manafold is glowing red, I bet it is.

The one comment you made about the pressure not holding for 5 secs after the engine shut off really makes me believe you have a pump problem. Either the check valve has gone bad in the pump, or the hose between the bracket and pump is shot.

[fengler]

did you ever figure out your problem?

[litdog]

You missed my point completly --

For ever psi of boost, you should be gaining 1 psi of fuel pressure (which is why it's a bad idea to take the vacume hose off the FPR)-- also as load increases, so does fuel demand, so when you drive down the road, and romp on it, the fuel pressure may be dropping, instead of increasing.

which is why you need to run a fuel pressure gauge out the hood, and tape it down to the windshield, and drive it down the street.

After a run, pop the hood, see if the exhaust manafold is glowing red, I bet it is.

The manifold wasn't glowing red.

I ran a fuel pressure gauge out and taped it to my windshield before you posted all that. The fuel pressure raised with boost 1:1 just fine. Since I was running such low boost and my static fuel pressure was so high, I unhooked the vacuum line and tried running it. It ran like crap down low and spit gas, but nothing changed with the detonation, and fuel pressure stayed constant on the gauge just fine, so I hooked it back up. I was only trying to see if the high fuel pressure was what was causing the problem.


In the end, I managed to get rid of the detonation by retarding the timing a few degrees. Runs fine now, and I was able to turn the boost back up to 15+ psi with no hints of detonation at all. I may try bumping the timing back up a degree or so at a time to see where it ends up. I had a similar detonation problem with my Grand National with a chip burned for 91 octane (best I can get here in Oklahoma, and it's still crappy gas), so I believe it was just a combination of the timing maybe being a little too high and the gas here.

Anyway, the car seems to pull about right now for what's done to it, has no detonation in any gear at 17 psi, and seems to run good all around. I still plan on eventually upgrading the fuel pump and regulator, it's just not as big of a deal now.

[NavySVO]

It ran like crap down low and spit gas,

It spit gas? Where from? If it was puking out of the FPR vacuum port, that FPR has a leaking diaphram and needs replaced.

[litdog]

It spit gas? Where from? If it was puking out of the FPR vacuum port, that FPR has a leaking diaphram and needs replaced.

I know that...

by spit gas, I guess I was meaning out the tailpipe... way too much fuel...

But anyway, the car's working fine now.

[svobud]

In the end, I managed to get rid of the detonation by retarding the timing a few degrees.

That doesn't make sense seeing how you stated in the beginning of this thread that you were running 5* and had detonation ... then bumped it to 10* (which would certainly cause even more detonation.) So, exactly what timing are you running now?

Mechanical problems just don't fix themselves - and you're saying it was low octane gas and too much timing? Even with 91 oct - it should have carried the boost to 10lbs with 10* of timing fine.

Lastly - why are you buying gas in Oklahoma if you're having your profile location as Missouri? You need to fix that to show your proper location ASAP.

[litdog]

It's called college.

I don't know what all was the deal back when I started this thread, and I'm not too worried about it. It may have to do with the weather being 90s+ when I started this thread, and 50s- now... who knows...

It works now, and that's enough for me until I graduate in a couple months and can afford to buy parts.

[svobud]

It's called college.

I don't know what all was the deal back when I started this thread, and I'm not too worried about it. It may have to do with the weather being 90s+ when I started this thread, and 50s- now... who knows...

It works now, and that's enough for me until I graduate in a couple months and can afford to buy parts.

Show one location - your actual location there Big Time College guy, not the one where your parents live.

As for your tech woes - guess we'll see you bring this thread back up when the weather warms up - as you never *fixed* your problem, huh?

[litdog]

Show one location - your actual location there Big Time College guy, not the one where your parents live.

As for your tech woes - guess we'll see you bring this thread back up when the weather warms up - as you never *fixed* your problem, huh?

Nah, I think i'll just jam the wastegate shut and drive it like that on 87 octane and 20 degrees of timing, because I obviously have no idea what i'm doing.

I won't be bringing this thread back up, as most of what I seem to get here is people talking down on me like I have no idea what a car is. Maybe my problem is fixed, maybe it's just a bandaid. If a problem comes back up later, i'll end up figuring it out myself like usual. Either way, it's my name on the title, not yours, so if I am ok with how it is running, then that's final. There is no use trying to bring down an honest ask for help to an internet boxing match.

[svobud]

That earned you a degree in what not to say to an admin.

[Bruce]

I know this is a foolish question but-do you know that TDC is TDC on your pulley? I have underdrive pulley's and the graduations are off! This was a real treat when I installed new valves and springs back in the day! Couldn't figure out why there was no compression for a while!