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Help me figure this out please!

Old 12-22-08, 12:14 PM
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Question Help me figure this out please!

I've been having a serious problem with my racecar for the past several sessions I've taken it out. In fact it's existed in some form since I've had the car, despite me having changed pretty much every single thing on it. I will try and explain the problem and my setup.

Setup: The engine is a bridgeported 13B-RE, with a GT35R 1.06A/R from A-spec on an HKS Manifold using an HKS Wastegate.

I am using an ATL 15gal fuel cell with a Fuel Safe surge tank inside it. I have plumbed the return line directly back into the surge tank such that it should literally, always be full of fuel. My fuel pump is an Aeromotive A1000 which has an Aeromotive 100micron filter before it. The lines are -10 coming from the surge tank all the way to the fuel pump, then -8 from the fuel pump to the primary rail, where it loops to the secondary rail, then back to the FPR, and back to the fuel cell via -8 as well.

The wiring for the entire car is all from the Painless Wiring 8-circuit racecar harness, with the exception of the fuel pump which I wired to a separate relay using 10ga wire as recommended from Aeromotive. All my battery wiring is 4ga and the alternator to battery is 8ga. There is a kill switch in the rear which all the battery wiring runs to and from.

The ECU is a Haltech E8. The coils are LS2 truck coils wired very well (if I do say so myself!), injectors are 850/1600cc, the rest is pretty much standard.

The problem: When I am exiting a corner, or during high speed corners, I sometimes experience what can only be described as the same feeling as hitting a rev limiter when I get on the gas or give it any throttle. At first I was certain this must be a fuel starvation/slosh issue so bought a surge tank and did a bunch of mods related to fuel like getting a new filter, re-wiring it with 10ga wire, etc. However, having looked at my datalogs for the past few sessions and watching the dash carefully, I experience absolutely no fuel pressure drop when I am experiencing this phenomenon.

I do not experience this problem on the dyno, and we performed literally dozens of pulls this past weekend without a hiccup of any sort.

I was so convinced this was a fuel issue that I remounted the pump under the cell, redid all the lines inside the fuel cell (from the surge tank to the top plate), ensured that the surge tank was sitting flat on the base of the cell wedged via foam, etc etc. However the fact that I maintain solid fuel pressure for the duration of these 'cuts' is making me wonder if it can be related to the fuel system at all.

If not the fuel system, what the hell else could it be? Driving me insane as I feel like I have fixed, re-fixed and replaced almost everything on the car at this point. Your thoughts are welcomed and greatly helpful.
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Old 12-22-08, 03:10 PM
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Since it's always happening under high lateral Gs I'd look for anything that can shift at all side-to-side. Probably focus on ignition wiring? A fueling issue would have sent your EGTs through the roof; fuel without spark should drop them considerably, right? Have you got EGTs in the data?
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Old 12-22-08, 03:57 PM
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agree with above. check for wire connections that might be getting lose or touching metal. wires to rub on insulation sometimes. so check all wiring if not a fuel issue. ive had this happen on a car. in my case it was a dizzy wire connection that was seperating
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Old 12-22-08, 04:18 PM
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Does it happen in right and left turns or only one or the other?
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Old 12-23-08, 01:12 AM
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It seems to happen equally on right and left turns. I've checked and re-made so much of the wiring that I can pretty much verify that it is as good as perfect.

I was examining the datalogs today and there does appear to be a very brief moment where fuel pressure drops while boost remains constant, so maybe it is a fuel issue after all. I am using the Fuel Safe surge tank but it appears to be not so good in a turbo car, going to try the ATL 3-door version and see how that does.
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Old 12-23-08, 02:22 AM
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why not make a full gallon or so aluminum surge tank and not a in cell one? would be much more beneficial if your running any longer races.....
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Old 12-23-08, 08:33 AM
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Originally Posted by thetech View Post
I am using the Fuel Safe surge tank but it appears to be not so good in a turbo car, going to try the ATL 3-door version and see how that does.
No answer as to what is causing your problem but I'm not following why changing the surge tank is going to do it. The only difference between the Fuel Safe and ATL ones are Fuel Safe uses a ball check valve and ATL a trap door, both have 3 inlets/outlets on them.

Are you thinking that under hard cornering the fuel is not being held in the surge tank by the ball check valve or ?

If you go out on track with a full cell of fuel and have the problem, there is no way it's going to be related to any pickup in the tank. I assume you have at least a 8 or 10 gal cell. Do you have the problem on a full cell of fuel?
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Old 12-23-08, 08:38 AM
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Originally Posted by SCCAITS View Post

If you go out on track with a full cell of fuel and have the problem, there is no way it's going to be related to any pickup in the tank. I assume you have at least a 8 or 10 gal cell. Do you have the problem on a full cell of fuel?
Excellent point.
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Old 12-23-08, 09:10 AM
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Originally Posted by SCCAITS View Post
Are you thinking that under hard cornering the fuel is not being held in the surge tank by the ball check valve or ?
thats what i was thinking
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Old 12-23-08, 12:51 PM
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Probably a dumb idea/question, but have you checked the spark plugs? We chased an issue like this once that turned out to be a broken plug... the boot held it together enough that we never saw an issue unless we were on a bumpy part of the track.
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Old 12-23-08, 05:24 PM
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Originally Posted by SCCAITS View Post
No answer as to what is causing your problem but I'm not following why changing the surge tank is going to do it. The only difference between the Fuel Safe and ATL ones are Fuel Safe uses a ball check valve and ATL a trap door, both have 3 inlets/outlets on them.

Are you thinking that under hard cornering the fuel is not being held in the surge tank by the ball check valve or ?

If you go out on track with a full cell of fuel and have the problem, there is no way it's going to be related to any pickup in the tank. I assume you have at least a 8 or 10 gal cell. Do you have the problem on a full cell of fuel?
I've had these thoughts as well, my cell is 15 gallons. The main difference between mine and your setups are that I am turbo and you aren't basically, as well as me using a -10 pickup from the surge tank. I am experiencing this phenomenon on a full-to-the-brim cell, which I agree makes no sense. The only thing I can think of is that for the brief moment where my fuel pressure goes from 35 to 52 psi a vacuum or air pocket of some sort is forming around the pickup point and causing this very tiny loss of fuel pressure. I am no expert of fluid dynamics so don't even know if this is possible; I do know that fuel that leaves needs to be replaced by air (hence the vent) so it's possible that a bubble forms for a split second. In your setup the fuel pressure is always constant so maybe this is why you don't experience this?

The main difference with the ATL tank as far as I can see is that the pickup is sealed to the floor of the surge tank and has a bunch of little holes where the fuel gets sucked in from, as opposed to our Fuel Safe setup where the pickup is raised off the floor of the tank. I'm not sure if this is going to solve the problem at all or if I should try using an external surge tank/swirl pot setup.



Originally Posted by gkmccready View Post
Probably a dumb idea/question, but have you checked the spark plugs? We chased an issue like this once that turned out to be a broken plug... the boot held it together enough that we never saw an issue unless we were on a bumpy part of the track.
Yup, plugs are new as is basically everything else on the car at this point (wires, coils, etc).

Last edited by thetech; 12-23-08 at 05:37 PM.
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Old 12-23-08, 07:03 PM
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hey mate,

We experienced the exact same problem in our race FD, with a very similar fuel setup to yours, we just couldnt figure it out, tried everything and nope, still happening even with full fuel (same as you I believe?)

Turned out to be injector staging and a bad tune (not suggesting you ave a bad tune ), with the large secondary injectors that we were running the crossover/transition point where the secondary injectors begin was very rough and at certain rpm/speed/high load conditions we would get the jerking similar to what you describe.

We got the thing tuned properly - with particular attention to fine tuning the transition and staging of the injectors (we really had to work on this on the dyno to get it perfectly smooth)

If this is the case the drop in fuel pressure you are seeing is the point were the secondaries come to life and it takes a tich for the thing to adjust itself...

Not sure if its what you are talking about, but that ended up being our problem and now it runs smooth like butter =] so hope it helps
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Old 12-23-08, 07:20 PM
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Originally Posted by alex.hay View Post
hey mate,

We experienced the exact same problem in our race FD, with a very similar fuel setup to yours, we just couldnt figure it out, tried everything and nope, still happening even with full fuel (same as you I believe?)

Turned out to be injector staging and a bad tune (not suggesting you ave a bad tune ), with the large secondary injectors that we were running the crossover/transition point where the secondary injectors begin was very rough and at certain rpm/speed/high load conditions we would get the jerking similar to what you describe.

We got the thing tuned properly - with particular attention to fine tuning the transition and staging of the injectors (we really had to work on this on the dyno to get it perfectly smooth)

If this is the case the drop in fuel pressure you are seeing is the point were the secondaries come to life and it takes a tich for the thing to adjust itself...

Not sure if its what you are talking about, but that ended up being our problem and now it runs smooth like butter =] so hope it helps
Wow, this is a very interesting revelation! What size primary/secondaries are you using? I am using 850cc primaries with 1600cc secondaries. Also, if this is the case, why does it only happen in cornering type situations? We did dozens of 4000-9000rpm pulls on the dyno and never had this issue - why would it only manifest on the race track? Did you have any trouble on the dyno as well?
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Old 12-23-08, 11:07 PM
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Where in the corner is this happening? If it happens when you are getting back on the gas and going to full throttle, that would fit perfectly with alex,hey scenario.
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Old 12-23-08, 11:49 PM
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Originally Posted by Chedstar View Post
Where in the corner is this happening? If it happens when you are getting back on the gas and going to full throttle, that would fit perfectly with alex,hey scenario.
It's happening on corner exit under throttle, but I still don't understand why, if it is what alex describes, this would only happen in corners? Surely it would manifest itself on straights, on the dyno, etc as it would be more a function of the staging than the corner.
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Old 12-24-08, 01:20 AM
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Originally Posted by thetech View Post
Wow, this is a very interesting revelation! What size primary/secondaries are you using? I am using 850cc primaries with 1600cc secondaries. Also, if this is the case, why does it only happen in cornering type situations? We did dozens of 4000-9000rpm pulls on the dyno and never had this issue - why would it only manifest on the race track? Did you have any trouble on the dyno as well?
yea we use 850cc primaries & 1600cc secondaries as well,

what we found was that it only occurs at certain load/rpm conditions, which for us was at load accelerating out of corners (about 100-120% load @ 3500rpm odd), unless these conditions aligned we wouldn't have a problem, so on straights etc you face different load conditions vs. in corners so we could revving it right through the gears no problem, same as certain low speed corners, thats why when it happens you back off the throttle and can get back on it once the load conditions change (ie. your through the corner exit) and not have a problem.

Ours also didnt show up on the dyno, because we werent looking for it... we did many pulls without problem, but you guessed it, because on the dyno the load conditions werent being met, so it went un-noticed. have a look at your datalogger, in particular rpm/injector duty and see where the secondaries kick in, if this is the same place you are having the problem (check AFR - ours went all sketchy at this point) then hit the dyno and have a play with the loads around this point and you should be able to make it happen, then its just a case of fine tuning the fuel delivery and injector loads/staging around this area (not sure about the haltech, we use an autronic sm4, really great tune ability), and you sould solve the problem completely!

hope this helps


Alex
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Old 12-24-08, 01:23 AM
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Thanks very much Alex, very helpful. After looking more closely at my datalogs its become pretty clear that after reasonably high G cornering (0.80-1.00+) I am experiencing a fuel pressure drop, sometimes significantly (down to 25psi). I think I will try the external surge tank setup and see if that does anything first, then re-hit the dyno if it's still problematic. Thanks for everyones input!
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Old 12-24-08, 03:45 PM
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Maybe the sock filter thing on your pump isn't in prime shape and it flexes under cornering load, causing a temporary clog?
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Old 12-24-08, 05:36 PM
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Originally Posted by Gene View Post
Maybe the sock filter thing on your pump isn't in prime shape and it flexes under cornering load, causing a temporary clog?
The pump is external and using an Aeromotive filter (brand new as well!)...I think my plan is to do the external surge tank setup, try and recreate/fine tune on the dyno, and then hit the track again and hope for the best!
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Old 12-26-08, 02:40 AM
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G'Day gents,
Very interesting reading this thread! I do have one question somewhat off topic - why go with the 850 leading injectors? I'm working on a 20B project atm and have changed the trailing to the Bosch Indy Blue 1600's, but was planning to leave the leading injectors standard. Once said, this is a street car by design, and will only be working till 7500rpm, but I'm wondering what I would gain by using 850 primary injectors.
Hope your problem is fixed btw!
Cheers!
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Old 12-29-08, 08:07 PM
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I saw a similar issue when I was first tuning my RX-7. I changed my fuel rails from serial to parrallel using a Y-connector. My theorywas at certain loads I would get the primaries pulling too much fuel and the secondaries were starving out. All I changed was to go to an aeromotive pressure regulator and run the primaries and secondaries in parallel. That seemed to eliminate the issue completely.

Hope this helps,

-Trent
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Old 12-29-08, 09:40 PM
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Originally Posted by TrentO View Post
I saw a similar issue when I was first tuning my RX-7. I changed my fuel rails from serial to parrallel using a Y-connector. My theorywas at certain loads I would get the primaries pulling too much fuel and the secondaries were starving out. All I changed was to go to an aeromotive pressure regulator and run the primaries and secondaries in parallel. That seemed to eliminate the issue completely.

Hope this helps,

-Trent
Now this makes alot of sense too...again, only confusion would be that it should happen on the dyno too. I'm going to replumb in parallel and get back on the dyno and see if I can recreate it...thanks all for the suggestions and comments.
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