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

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.

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....

can you monitor fuel pressure?

Jody

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

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

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.

http://i168.photobucket.com/albums/u...Picture081.jpg

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................ :P but just as a quick check I've never had an issue.

Jody

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.

67rag --

Jody / Frank ....

This is the same motor - with the dyno sheet posted earlier in the thread - that has (IMHO) VERY lean conditions - especially at peak torque and WOT... they were in the high 13's and low 14's at peak torque....

So if he's 'running' lean - it could be a lean miss - even with low load conditions - and he said he's observing A/F's on the dashboard at 14.5's and even as high as 15. I'm ASSuming that they observed these readings while cruising at the "trouble" point. I'm thinking if he's seeing 15 A/F readings -- he's feeling a lean miss...

If his VE's are close -- I wonder if he couldn't change the "BLOCK" of A/F at his trouble spot -- to something like 13.4 or 13.6 etc -- while driving === and see if the miss/hiccup goes away. If it does - then it's just a matter of finding the leanest A/F ratio he can run at that Map point... and run with it. If it's still there -- then we know it's not a lean miss -- and he can start working on more "complicated" solutions?

OOOPPPPSSSSS ----

Wrong - my bad -- one guys is 61 Ragtop and this guy is 67Rag ---- so sorry --- I was going to reference the post with the dyno sheet -- and realized I had the wrong car.

However..... I'll stand by my statement of trying to fatten the fuel a bit and see if there is a lean miss - given his observed 15 A/F readings

true, but at a cruise MOST combos can be leaner than 14.7:1, however not all so it's a legitimate thing to test. Of course, if the pressure is fluttering you can try changing the a/f or v/e tables and cannot cure it as the pressure is moving all around.

Jody

Jody,

Ah ha -- Got it.

So how steady should the needle in the gauge be when running? With the pump pulsing - my gauge vibrates a lot - but my gauge is in the line not in the regulator.

I was reading my install instructions for my XFI and you can connect a sensor directly to the ECU . It has wires for sensors built in.
I don't know squat I'm just learning but I hope this helps . Wayne

This connector houses the 8 analog inputs that can be used for things such as fuel pressure sensor, oil pressure sensor, EGT probes, etc. An Analog Auxiliary input harness kit (part # 30-1402) is available from FASTä.

Pin A – AAUX1, blue/gray (C12)

Pin B – AAUX2, gray (C13)

Pin C – AAUX3, purple (C14)

Pin D – AAUX4, light green (C15)

Pin E – AAUX5, yellow/black (C16)

Pin F – AAUX6, blue (C17)

Pin G – AAUX7, brown/white (C18)

Pin H – AAUX8, white (C19)

Pin K – Analog return, black (C11)

2.1.20 AUX SHAFT

This connector is for the auxiliary shaft sensor input circuit. The FASTä VSS and auxiliary shaft harness kit (part # 30-1403)will supply you with the harness, sensor, and magnets to monitor things such as turbo speed and torque converter/clutch slippage.

Thanks guys, I guess I will pick up the FAST fuel pressure sender kit(301408), this way I can dat log the pressure and A/F ratio while it occurs.

If the pressure is fluctuating, any Idea what the solution would be, should I move the regulator to the firewall?

Thanks Rich

relocating the regulator may be an option, wait and see if the fuel pressure is steady or not. Did you try richening the tuning in the area that it occured in?

Jody

Well we bumped up those areas in the v/e table by 2 numbers and brought the a/f ratio map in those areas from 14.7 to 14.3 and it didnt seem to help. That should have added a bit more fuel(I think). I was a bit nervous about making a big number change in the v/e table. If I raise the v/e table numbers will the air fuel ratio automatically richen up or does the A/f map while closed loop automatically compensate to hold that A/F ratio. Should I really change the numbers alot?

I hope Jody will add to this -- but VE's are the efficiency of the engine at a particular MAP point... once the VE is "on" -- then you should leave that alone and just change the A/F ratio that you want to run at that spot. Check your O2 sensor readings -- and if the motor is 'putting out' the A/F ratio that you've set and it's not adding/subtracting more than say 5% -- then I'd just leave the VE where it is.

I have Accel -- so it's hard for me to tell you what your screens are... but the Accel has a 'screen' that is similar (I think) to the Fast system - where you can see a scale of what the O2 sensor is doing.... and if the VE is on the money - the O2 sensor is doing 'little'. That would mean the VE would be right on... If the O2 sensor is adding and subtracting 10 or more % - then that should be corrected first. Once the VE is on - then you should be able to change the A/F ratio and the ECU will just simply figure that ratio out and that's what the engine will get.

Does that make sense? Ideally -- you'd want the VE table so well set - that the O2 sensor is just along for the ride. That is not always possible of course... but if the VE tables were perfect - you wouldn't even need an O2 sensor.

getting the VE's right with the O2's working as little as possible is the goal. But if you change the a/f desired at a particular range the VE will also change to keep it ideal. I treat the VE table like jet sizes, larger numbers are richer and smaller are leaner, so if you change your a/f table you'll want to dial in the VE table as well.

In closed loop the computer will compensate by adding or subracting fuel to reach you desired a/f. You can limit how much it adds or subtracts in the tuning software, usually most aftermarket systems have a max limit of 25% +/-. That means if your VE table is within 25% of the ideal number to reach your desired a/f number, then the computer will automatically add/subtract to get you there. Your job as the tuner is to get you there without a lot of computer intervention, so it still has room to add/subtract fuel due to varying conditions like temps, baro changes, etc.

Jody

Jody --

I was trying to get him to understand the VE --- get that close --- then leave that alone and fatten up the A/F... figuring that going from 14.3 to say 13.8 wouldn't "disrupt" the VE much.

I personally like to not make too many changes in too many tables - when trying to sort out a problem. Since he's happy with the tune - except just this one area he described... I was kind of thinking that if his VE is okay - then he could just change the one table (A/F) and see if that's the issue (a lean miss?).
Rather than messing up the VE table AND the A/F table too... if you get my reasoning?

I agree - that if - lets say he fattened the A/F to some point - and the miss went away... then he could go back and make sure his VE was accurate?

I might be wrong here - so I'm glad you chimed in.

I actually like working in my A/F tables and VE tables with the O2 in open loop... and when I'm seeing A/F's that match my desired A/F's with no correction - then I switch it back to closed loop... but I didn't want to complicate matter for him either.

you're right, assuming he has enough correction set up in the software he could simply adjust the a/f and let the competer adjust the ve to get there and see if it solves his issue.

Jody

I appreciate all the input from you guys, I ordered the fuel pressure sender kit from FAST today and will hook it up and head to the highway this weekend. This way I can data log whats happening with A/F ratio vs fuel pressure and look at all the paremeters, once I have this data I will let you guys know.

The closed loop correction limits at the area(52to 58kpa-2.0k-2.4k rpm, light cruise) that IM having problems is -25% and +22%

Thanks for all the help, more to come- Rich

Well I installed the fuel pressure sender and hooked it up to the ecu. Seems accurate, the regulator is vacuum referenced so my idle pressure is right around 40psi. If I pull the hose off the regulator it goes up to 44-45psi.

I had the opportunity to get it out on the highway for a solid 1 hour of highway time and data logged two 30 min sessions. Its at least 15 to 20 degrees(70F) warmer out than it was when the stumbles were occuring during last weeks criuse(52F). I let it idle in my driveway for 10 to 15 min hood closed to get it really warmed up before we hit the highway. Were cruising at 2200 rpm and at around 22 minutes into the first cruise we feel a very slight stumble and thats it the second 30min never felt a thing. So I look at the data around that time and I dont see anything major. The average fuel pressure is between 36 and 40 psi the actual A/F is around 14.5. I noticed the fuel pressure tracks the KPA graph very closely, I imagine this due to the vacuum reference. When I roll out of the throttle and rpm comes down getting off the highway the kpa goes down significantly(18kpa- 36psi) as does the fuel pressure. I really thought the stumbles would happen more frequently since it was warmer out but it didnt. Does the colder air make it much leaner? What do you guys think?

Thanks Rich

FWIW, I really enjoy reading this type of thread...I always learn something if not lots!!

Rich, you and the boys will figure it out!! :thumbsup:

Rich,

Okay -- Jody will correct me on this... but there is no reason at all to have the vacuum reference on the fuel regulator. That application is only for boost reference. But - if it was tuned with the vac applied - it should be okay. There's just no reason to have it. However, DO NOT plug the vacuum port of the regulator. It needs to be open to atmosphere.

I've been told that the IAT (Intake Air Temps) have very little to do with the actual references used in the ECU... I've been told this by at least 3 different tuners... but then - they could all be wrong too. Since I have 8 stack EFI - my IAT sensor is just kind of "hanging" between a couple of the stacks back at the rear of the engine. I've put it in a couple of places - and it doesn't seem to make any difference in anything.

Since your 'issue' seems to be so intermittent... I think I might be looking for an electrical draw. Maybe the voltage drops when something goes on? Causing a momentary blip in the ECU/sensor voltages.

I'd also be looking for a possible "hole" in the VE or A/F map - where your foot (TPS or MAP) just drops into this hole. If you have 3D visual on your system - look to see the junction at the perceived RPMs/Map signal (like 2200 rpm and 45kpa -- or wherever you think this fault happens) and see if there is a dip in the map or a "mountain" right around there...

Last thing I can come up with to check on - the voltage to the Fuel pump... I'm assuming you're running it off a relay.... and that it has a great ground system... and that it's not dropping voltage momentarily when your fans kick on - or the stereo kicks on - or the A/C compressor goes on etc.

I'm assuming also that you're using a ONE WIRE type alternator charging system (with no points style voltage regulator in the system) and that the alternator is capable of handling the total loads placed on it (i.e., the amp draw has been added up for all your systems and that the alternator is capable of supporting them all).

LAST... there has been some discussion about faulty MSD systems. Can't remember where this thread was - but there was an issue with them heating up and breaking down. One guy was icing his down for awhile until he sent it back for a factory look see... I just don't remember the issue or the outcome.

Rich,

I might add that I also think the cruise temps you mentioned (in your first post) could be part of the problem. Your first post mentions (proudly!) that your engine temps were around 165 degrees (if I remember right) and this could be causing the fuel in the intake to not stay atomized... and might help explain why - today - with the warmer air temps - your problem wasn't happening as much.

I raised my thermostat to 195 degree version. EVERYTHING works better now. The pistons (forged) seal better - I use less oil - and the motor just purrs... I also have a 427 small block. New fuel injected motors are running 200 degrees plus at operating temps. This is due in part to emissions (I think) - but I also think it helps with fuel injection.

Just a thought is all...

For what its worth, monitoring battery voltage in the data logs only one tenth of change from 13.5 13.6 occured. I do run a relay to the fuel pump and the grounds are real good. I tied the whole car together with 4 10guage multistrand wires lugged into a 4 guage lug terminals and mounted them everywhere. The fuel pump pulls power through isolated 8 guage wires directly from the battery back to the terminals on the relay in the back of the car.

The log did show an average of 175 deg of coolant temp. At that temperature if Im running a 180 tstat isn't it closed. The water temp had to be close to 10 degrees colder last week.

Rich,

Grounds and pump seem fine! Good job.

I'd love to hear what some of the more knowledgeable folks here think of the water temps. Yes - at 175 your thermostat would be closed. That is still a very COLD temp to be running - especially with forged pistons... they love some heat. And it just might explain the stumble... but I'm just guessing here now anyway.

what does the ignition system consist of ? What are you using to trigger the XFI crank signal ? cam signal ? where are the pick ups located ?


where is your coolant temp sensor for the efi located ?
do you have a temp guage also ? what does it read and where is it's sensor ?

FAST Dual sync distributor/MSD 6a/MSD blaster HVC(blue body)

Coolant sensor is front of the manifold under thermostat, ECU matches the guage. The one in the foreground is the ecu(black and white wire)
http://i168.photobucket.com/albums/u...Picture435.jpg

Holy cow - I was looking all over for that piece of rubber hose sitting at the bottom of the manifold HUH -Rich

Ok, the dual sync probably rules out over heating magnets getting weak and causing a bad signal. I planned on using my Mallory distributor as a cam sensor and a homemade crank trigger to get the crank signal. The rare earth magnets I put into the damper were too small and when they got hot, I'd loose the signal. It took me a while to figure out what was happening - magnets get weaker as they get hotter who knew . I haven't yet replaced the magnets, so I'm just using the distributor for a crank signal.

I'm going to guess you've got a thermostat stuck open - either jammed with something or just failed. Is that the cause of the stumble ? IDK, but I'm guessing you will let us know !

Wedged -

He does seem to running "too cool" IMHO... and ECU's use ECT (engine coolant temp) for a LOT of control of fueling etc... So, too cold could cause him some 'errant' issues.

Thermostats don't usually fail "open" unless he has that type.. there is a type that fails open. I'm wondering if his thermostat is running within it's operating range... i.e., 175 degrees actual reading for a 180 thermostat seems within range? But I do think it's a bit cool for the application....

RICH -- Nice storage place by the way. I keep rubber hose there all the time... it keeps it soft and pliable - well - until it's been heat cycled a few times - then it can get dried up and a bit brittle. <grin>

Rich --

I'd forgotten about this - but one time I had an errant "stumble" - but it was at any time - any place... I finally found it was one of the connections at the distributor - the "clip" on the weather pack connector wasn't clipped - it looked like it was but just wasn't quite. Once fully engaged the problem went away. Also had a bad Dual Sync one time - something with the circuit board - replaced it and have had total reliability ever since. That was very early on in the Accel EFI years (something like 8 or 9 years ago at least). They used to have too small of a wire harness coming out of them (too small and too stiff too!) but they've since changed that.

I'd leave the tune alone, to me sounds like a poor connection or possible ignition issue. You can hit the wires with a quick mist of water from a spray bottle. That should atleast rule out an errant issue there. Night time usally works best to see cross-firing etc. Sometimes a cracked plug can do the same thing.

As Greg pointed out, I'd double check the connections in the distributor and injector harness. Usually a misfire or stumble should show itself in the O2 log. If your not seeing it, maybe you need to look to the opposite bank for possible issues.

Changed my plugs today and then took a peek inside the cap. Why does the inside of my distributor look like its been living below sea level. The screws to get the rotor off were actually furry, and the distributor plate completely rusted . This thing is a couple years old with about 500 miles. Im thinking the level of moisture inside the cap has to be very high. Wonder if this is causing my miss?

http://i168.photobucket.com/albums/u...Picture453.jpg

http://i168.photobucket.com/albums/u...Picture452.jpg

http://i168.photobucket.com/albums/u...Picture449.jpg

http://i168.photobucket.com/albums/u...Picture447.jpg

Rich

Wow thats in tuff shape. That would definately cause problems. I don't know if its all of your trouble but might be big part of it.
Rich do you have a Batery disconnect on your car ? It almost looks like electrollises on a boat.

Wayne- no disconnect, but I did probe around with my DVM and theres no voltage at all on the primary side of the coil when the key is off. And there's no current draw off my battery with key off either.

The black cap in the pic that came with the fast dual sync distributor does not have a vent in it. I wonder if thats part of the problem. I just installed a new msd cap with a vent, it seems to be running well in the garage but havent had a chance to get it out. I switched sparkplugs from accel 416 to NGK FR5 , I hope the heat ranges are pretty close, I noticed the white portion is protruding out a little more than the accels. The accel spark plug also has a screw on terminal end and it always annoyed me that no matter how tight you make them they always loosen up.

Maybe the weather will be better tomorrow to take a ride and check it.

Wow buddy! That's nasty and MOST CERTAINLY would/could cause your issues!!

Glad you found that "scank" even if it wasn't the problem!! That is a problem in the making!