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Old 09-26-2009, 04:18 PM
67ragtp 67ragtp is offline
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Default FAST XFI tuning question

Heres my scenario, Im driving out to pocono for the good guys event early this morning its about 50 degrees out might have been in the 40s never had this car out for a long haul. just local cruises, but it was tuned by a professional tuner on a dyno with a eddy brake and suppose to be dialed in for cruise/WOT/cold start and all that stuff. Its a 427 mitchell sb with 42 lb injectors on a sigle plane with a fairly mild hyd flat tappet. So the 100 mile cruise up there although cold was flawless not a hicup. Noticed that my water temps were barely 165(big RD radiator and cold out).

The ride home its a bit warmer but not much maybe 55 degrees but the water temp at times would be between 165 and 180 after about 50 miles at between 2000 an 2300 rpm cruising in 5 th gear at around 70mph it would periodically stumble. It was like a jerk in the engine some times heavy and sometimes light. Like a hiccup. So Ive got the wife in the passenger seat and we pull out the lap top and plug it in. As the hiccups are occuring every so often we are monitoring were the foot ball is in the VE fuel table. So we increase those numbers from 34 to 36 around 52kpa then we go over to the A/F ratio map and change those numbers from 14.7 to 14.3. Im thinking Im adding a bit more fuel and this is a lean stumble but it really doesn't do anything with these changes. I remember getting this type of stumble on a very hot day about a year ago when I jumped on a higway. My wife said the actual a/f ratio was averaging 14.5 to 14.7 with moments as low as 13.8 and as high as a 15

Could my under hood temps be causing this and how do you tune it out? I just have a feeling the hotter it is outside the worse this will be, any suggestions?

Thanks Rich
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Old 09-26-2009, 05:56 PM
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GregWeld GregWeld is offline
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Rich --

I'd take it back to the tuner and have him try to duplicate your issue.

My 427 small block runs an Imagine Injection 8 stack --- and at that cruise speed I'm running 13.8 A/F. The 8 stack seems to need a bit richer A/F - or so it seems.

The VE you adjusted is the most important function -- once that is "set" correctly -- then you can play with A/F and the ECU will just make that A/F happen.

You didn't mention your TIMING -- and you could be seeing a timing issue right there? Too much advance might give you a hiccup. The new heads etc tend to take LESS timing than in the old days. But you're description was to paraphrase - light load - cruise... so I'm only mentioning timing because you didn't give a number for that area.

Now -- I've increased my thermostat to a 195 degree, up from a 180 -- and have the fans on a Spal PWM (pulse width modulated) controller... and I'm cruising around 200 degrees. I like more heat - because with the forged pistons -- I want a bit more sealing (expansion). I'm running Amsoil 15/40 Synthetic.
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Old 09-26-2009, 06:03 PM
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GregWeld GregWeld is offline
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I'd also check all your plug wires -- look for any of them that "at speed" might be being blown against a header and have burned enough to short. It doesn't take much!

You asked about under hood temps... and you should have an IAT - Intake Air Temp - sensor... which really isn't that important of a sensor - but would accommodate / allow for - intake air temps.

Also -- the MAP sensor is critical... the signal to this should come straight from a source with no "t's" etc....
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Old 09-26-2009, 06:23 PM
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can you monitor fuel pressure?

Jody
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Old 09-26-2009, 06:26 PM
67ragtp 67ragtp is offline
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timing is 36 deg in the 2k to 2.4k @52kpa and 38 deg in the same rpm range at 46kpa.

I run those heavy heat isulating 6 inch booties at the end of each plug wire and there dressed securely.

The map sensor is one leg of a "Y" Tee connected to the back of the throttlebody, the other leg goes up the the vacuum reference port on the fuel regulator.

What I dont get, is why was it so perfect for the trip up and so different on the trip back.

Thanks Rich
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Old 09-26-2009, 06:28 PM
67ragtp 67ragtp is offline
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Jody- short awnser no, the fuel pressure guage is under the hood connected to the regulator. What are you thinking Jody, fuel pressure fluctuation with engine temp?
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Old 09-26-2009, 06:41 PM
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Quote:
Originally Posted by 67ragtp View Post
Jody- short awnser no, the fuel pressure guage is under the hood connected to the regulator. What are you thinking Jody, fuel pressure fluctuation with engine temp?
yeah, that can happen easily with the way some are plumbed, and usually are heat and distance run related. If the pressure is moving around at all, like the pump is cavitating from the fuel heating up in the tank, it's an immediate hiccup with efi. It's just part of the tuning process, and you need to be able to verify the basics at the time a problem occurs. Datalogging is great, but if the fuel pressure is moving it throws a wrench in the works.

When this was happening was the a/f moving around at all? Did you notice that the fuel pump was louder?

Jody
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Dakota Digital for their Chevelle HDX Gauge Package
Painless Performance for their wiring harness

Ron Davis Radiators for their radiator and fan assembly.
Baer Brakes for their front and rear brakes

Texas Speed and Performance for their 427 LS Stroker
American Powertrain for their ProFit Magnum T56 kit
Currie Enterprises for their 9" Third Member
Forgeline for their GF3 Wheels
McLeod Racing for their RXT street twin clutch
Ididit for their steering column
Holley for their EFI and engine parts
Lokar and Clayton Machine for their pedals and door and window handles
Morris Classic Concepts for their 3 point belts and side mirrors
Thermotec for their heat sleeve and sound deadening products
Restomod Air for their Tru Mod A/C kit
Mightymouse Solutions for their catch can
Magnaflow for their 3" exhaust system
Aeromotive for their dual Phantom fuel system
Vintage Air for their new Mid Mount LS front drive
Hydratech Braking for their hydroboost system
Borgeson for their stainless steering shaft and u joints
Eddie Motorsports for their hood and trunk hinges and misc parts
TMI Products for their seats, door panels, and dash pad
Rock Valley Antique Auto Parts for their stainless fuel tank
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Old 09-26-2009, 07:01 PM
67ragtp 67ragtp is offline
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While observing the actual A/F from the xfi dashboard it always seems to move around a bit up and down a couple tenths never rock solid on one number. We didnt catch it since it happens so sporadically(datalog would be nice)

I cant hear the fuel pump making any noise especially over the exhaust. What do you suggest for fuel pressure monitoring in the car, this is what the plumbing looks like.

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Old 09-26-2009, 07:45 PM
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a datalog of the problem would be nice, would at least give you a direction to go. I have an 8' extension pressure line I use for temporary checking of fuel pressure that I can run into the car, but I usually have a gauge in the dash. I know, you're not supposed to run fuel into the car................ but just as a quick check I've never had an issue.

Jody
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SPECIAL THANKS TO:
Jacob Ehlers and Amsoil for the lubricants and degreasers for my 70 Chevelle project
Shannon at Modo Innovations for the cool billet DBW bracket
Roadster Shop for their Chevelle SPEC Chassis
Dakota Digital for their Chevelle HDX Gauge Package
Painless Performance for their wiring harness

Ron Davis Radiators for their radiator and fan assembly.
Baer Brakes for their front and rear brakes

Texas Speed and Performance for their 427 LS Stroker
American Powertrain for their ProFit Magnum T56 kit
Currie Enterprises for their 9" Third Member
Forgeline for their GF3 Wheels
McLeod Racing for their RXT street twin clutch
Ididit for their steering column
Holley for their EFI and engine parts
Lokar and Clayton Machine for their pedals and door and window handles
Morris Classic Concepts for their 3 point belts and side mirrors
Thermotec for their heat sleeve and sound deadening products
Restomod Air for their Tru Mod A/C kit
Mightymouse Solutions for their catch can
Magnaflow for their 3" exhaust system
Aeromotive for their dual Phantom fuel system
Vintage Air for their new Mid Mount LS front drive
Hydratech Braking for their hydroboost system
Borgeson for their stainless steering shaft and u joints
Eddie Motorsports for their hood and trunk hinges and misc parts
TMI Products for their seats, door panels, and dash pad
Rock Valley Antique Auto Parts for their stainless fuel tank
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Old 09-26-2009, 09:09 PM
ProdigyCustoms ProdigyCustoms is offline
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That regulator is super close to the water pump. a very hot area of the eninge. I would get a electric fuel pressure gauge and if you dont ant to see it all the time, put it in the console for troulbe readings when needed. It is nice to have in a no crank, or fluctuation situation like this.
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