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Old 06-12-2004, 08:53 PM   #1
munkis
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Default grr. EGT's spike when letting of the gas (highway cruise) :(

im getting frustrated...

at this point I hope my egt gauge is borked...

If im on the highway in 5th gear cruising around 75 - 80 mph, at say 10 in/hg vac on the boost gauge.

if I let off the gas...the EGTs skyrocket...im mean skyROCKET! its bad enough they are at 1500 at cruise but if I let off the gas, the guage goes off the chart past 1600 for a about a second then there i hear some poping in the exhaust and the go back down to around 1200 or so.

any ideas why this would happen?



Jay
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Old 06-12-2004, 09:41 PM   #2
lotusTT
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what engine management are you running? It sounds like a tuning issue. Does it happen in any other gear?
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Old 06-13-2004, 12:47 AM   #3
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Definately depends what type of engine management you are running, if it is a piggyback this is pretty normal and nothing to be concerned with. If you are running a standalone, try enriching the mixture slightly under heavy decel and advancing the timing (if your standalone allows for this). You can get it to go away, but it's really not a big deal.
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Old 06-13-2004, 12:47 PM   #4
munkis
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thanks for the replys.

all I have is an SAFC and j&s knockguard.

Im having the safc dyno tuned this saturday, im hoping they can dial it in, cause I dont want to spend the money on a stand alone right now.

It will happen any time im at around 10 in/hg and let off, it will spike say im at 1200 it will go up to 14-1500 if im in 4th gear.

turbo kit includes..

EJ22T shortblock attached to 2.5 DOHC heads
Rallispec turbo setup includes-
-Turbonetics t3/t4 turbo with ported inlet housing
-Rallispec intercooler
-Greddy BOV
-Tial wastegate w/6 lbs spring
-3" Catback
-single high flow cat
S-AFC
J&S knockguard
MBC set to 10 lbs boost
400 CC/Min injectors
Supra Fuel pump
PiperCross intake
NGK BKR7E-11 Plugs
Magnecor wires
gauges - boost, EGT, oil pressue, fuel pressure + air/fuel ratio
Rallispec oil cooler


Jay
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Old 06-13-2004, 01:22 PM   #5
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Weird, I'm using a e-manage and I don't get this. So I don't think it is piggy back related. The only issue I have is trying to boost in 5th gear. I can't hold it in boost too long or it will go beyond 1500.
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Old 06-13-2004, 01:31 PM   #6
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Quote:
Originally posted by no-coast-punk
If you are running a standalone, try enriching the mixture slightly under heavy decel and advancing the timing
You can do this on the S-AFC as well, Jay. Remember those decel settings? Maybe just tweak them a bit and see what happens.
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Old 06-13-2004, 02:11 PM   #7
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sounds like you are running too lean.

1450-1500F is normal for cruise. When driving on the freeway the ECU will use the 02 sensor to find stoichemetric burn. This is to get better gas mileage

This is NOT good for acceleration. STOICH is too lean to accelerate. When you step on the accelerator, timing advances, and the fuel curve richens.

I have no idea why EGTs go up when u let off the gas. Generally they fall immediatly.

-Jake
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Old 06-13-2004, 02:18 PM   #8
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Quote:
Originally posted by 8Complex
You can do this on the S-AFC as well, Jay. Remember those decel settings? Maybe just tweak them a bit and see what happens.
Nick I have been playing with them and havent really had any luck, probably because I dont know what to set them at, or how the function works

Ive been assured the dyno place (turbotrix in edison NJ) are more than capable of tuning the safc.

Ill see how that works out, im not really gonna drive the car to much untill saturday.

on boost/acceleration, the egts drop nicely to around 14 hundered with the a/f going slightly rich, no problems there. I have to stay on the gas slightly to keep the egts from spiking when I get off the gas.

thanks for the replies guys keep'em commin, im trying to learn as much as I can about this tunign stuff.

I also concluded all the fuel I added up top on high and low thottle to try and bring the egts down on high boost/WOT did nothing but destroy my gas mileage. I set them back to the settings when I got the car (supposdly still the rallispec settings) and I get much much better gas mileage even on boost, around 18 - 22 mpg.

My problem seems to me, to be, Rich on low speed decel (flooding and stalling on decel) and lean on high speed decel. (egts spike)

Thanks!

Jay
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Old 06-13-2004, 02:35 PM   #9
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High EGTs can also mean you are running rich when lifting. Unburn fuel gets into the header and pipes you get an afterburn effect. Since your poping I would think of this also..
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Old 06-13-2004, 03:05 PM   #10
munkis
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Quote:
Originally posted by HOK
High EGTs can also mean you are running rich when lifting. Unburn fuel gets into the header and pipes you get an afterburn effect. Since your poping I would think of this also..
good point...

I do shoot fireballs 5 feet long on occasion...

That makes very good sence...yet opens up a bunch more things to think about lol

at highway cruies my a/f is stoich (sweeping in the stoich range) and 14.7ish according to the j&s a/f gauge.

so maybe im rich on decel all the time then...rather than my post above...

Jay
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Old 06-13-2004, 03:50 PM   #11
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Sorry i hit the submit button way too fast lol...

but i wouldn't do anything untill you get a wideband on the car... I would take it to the tuning center since you feel they are up to the task.. I'm assuming your AF meter is the christmas tree autometer version that really isn't any good.

but i would bet on rich more then lean in this case...
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Old 06-13-2004, 05:05 PM   #12
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hahaha, yes its a xmas tree lol.

Ill be sure to post back after the tuning is done.

Jay
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Old 06-13-2004, 05:57 PM   #13
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Why didn't you mention the fireball thing earlier? hideously rich mixtures and slightly lean mixtures can cause some of the same symptoms... just not the fireballs.

Very lean mixtures under a very heavy vacuum (heavy decel) burn very slowly and will continue to burn well into the exhaust system unless you advance the timing alot, or add more fuel for a faster burn rate. The popping sound is actually the combustion event finishing.

Excessively rich mixtures won't burn at all due to the lack of oxygen however under just the right conditions the valve overlap will allow a bunch of fresh air to be sucked into the exhaust and on DIS ignition vehicles, the waste spark happens during the exhaust stroke... these things all come together under just the right conditions to allow the fuel to burn all the way down the exhaust and out the tailpipe. Advancing the timing under this condition can be a double edged sword, advance it just right and you won't have the waste spark setting off the mix, advance the timing too far and you'll see detonation happen under heavy decel.

The sounds these 2 conditions make is slightly different, the lean afterfire is a higher pitched sound that sounds sorta like a string of firecrackers, the rich mixture has a much deeper sound to it and doesn't happen as quickly.

What you need to do with the AFC is go into the root menu, go to settings, and then go to Dec. Air, with as large as your injectors are, go to full lean at both NE point 1 & 2. Then set the throttle point below what you'd typically see during normal driving (2-4% is good).

Hope this helps
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Old 06-13-2004, 08:03 PM   #14
munkis
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Thanks for the help, ill do that 2morrow.

when im setting the decel air settings the higher percentege I go the leaner I go?

thanks for explaining how the function works, thats what I really needed.

so I will set them both to 20% IIRC thats as high as I can go and Ill start with the throttle at 3.5%.

Ill give credit to 8complex here to cause he did tell me something similiar without knowing exactly how the function worked himself.

thanks again!

when it shoots fireballs it sounds like an m80 going off, just like anti lag but only once, usually after a hard accel or high rpm downshift into 2nd.

Now that I gapped the plugs smaller the backpressure sound (rumbling/popping), hard to explain has gotten more frequent on decel...and I get more loud backfires than before.

im not sure if I should open the gap back up.. went from .044 to .030

Jay
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Old 06-14-2004, 12:04 AM   #15
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Does the J&S retard when you lift off the throttle? If so, which J&S do you have?

Engines often have piston slap on decel, which can fool a knock sensor.

Our early units have a wire to sense throttle position, and prevent the unit from retarding until the TPS is above 1.75v.

Our newer units have an onboard MAP sensor, and prevent knock retard if there is more than five inches of vacuum.
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Old 06-14-2004, 08:12 AM   #16
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Its an old one I think, I have no Idea what version it is, it never retards timing.

the red lights on top never come on. (except when it powers up)

How can I tell what version it is?

Jay
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Old 06-14-2004, 09:26 AM   #17
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Do you have a J&S bargraph display to show retard?

What color is the main J&S harness connector? Our early units had a dark brown one.
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Old 06-14-2004, 11:06 AM   #18
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His is a non-MAP based unit, but I don't know if it was a black or purple case.
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Old 06-14-2004, 01:25 PM   #19
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purple case nick, I think the connector is brown..
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Old 06-14-2004, 02:35 PM   #20
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If the J&S is not retarding on decel, then check your A/F ratio.
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Old 06-14-2004, 07:32 PM   #21
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setting the decel air settings both to 20% did not help. I tried 3% throttle, 15% and 20% high as it can go. Didnt really change much.

Ill see what they can do saturday on the dyno.

thanks for the help though

Jay

Last edited by munkis; 06-14-2004 at 10:40 PM.
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