Rear return system questions

[jjump59]

i asked this over at Pro-touring but should have posted here where we've disussed this system before so i'll put it here also.

Took my 70 GTO to the tuner, FAST XFI, aeromotive A1000 inside Ricks tank, Aeromotive return style regulator mounted at tank and Aeromotive filters. Everything is plumbed with -10 for feed and -8 for the short return. Right away he told me it would not work the way I had it, he was concerned about the fuel going through the regulator, he thought the regulator would be a restriction that would cause the engine to starve for fuel. He recomended putting an additional -10 hose using t-fittings at the inlet and outlet, bypassing the regulator to help feed the engine. Have you guys had any problems that required this kind of fix?

Second question concerns no fuel at rails during restart, I have to let the pump run two or three times before the car will start. it seems that the fuel is returning to the tank and not staying at the rails. kind of stinks having to turn the key on and off three times before it will start. any easy fixes here? maybe a check valve of some type?

thanks for the help guys.

[GregWeld]

I'm running a 427 cubic inch SBC -- with Imagine Injection 8 stack efi... 400 lbs RWTQ

I'm running -8 feeds and -6 return - with an aeromotive regulator... and electric pump @45 lbs of pressure.

My regulator is mounted CLOSE to the fuel rail - I feed one side - loop to the other side - and out - to the regulator.... I'm running 39 lb injectors.

My car starts instantly = just like a new factory EFI car does.

I think the problem you're having is too much distance from the rails to the regulator... the pump is having to build pressure from the regulator - back to the rails and all the way back to the pump -- you have HUGE lines.... so it's taking the pump a bit to build this pressure up.

Your "tuner" questions the size of the lines -- it's a mathematical equation as is the required size of line to feed and the size of the injectors. If you're feeding with -10 -- and the motor uses some of the fuel -- then -8 return should be plenty. I would question the -10 feed line -- you must have a HUGE engine!! LOL EEEEEEEEHHHHHAAAAAAA

[camcojb]

I have run the rear regulator system on several cars, they all started instantly. It takes less than a second for full pressure to the system. Basically by the time the key is turned on and you start cranking the starter you have pressure. No, the pressure doesn't remain in the lines, but it didn't when the regulator was up front on the rails either. I think you could do a one-way valve or specific pump that would hold the pressure for a bit, but most all the aftermarket stuff doesn't. Then again, it's never been a problem with mine that way.

I will say, the cold and hot starts are two areas of tuning that can take a while to get right; it's a balance of cranking fuel, IAC position, temp modifier tables, etc., and with the cold start you only get one try per day to get it tuned.

Jody

[GregWeld]

Excellent response Jody -- and you're spot on. I've warned many friends that EFI is not for the faint of heart... and that dyno tuning is fun and gets the big stuff out of the way... it can take days of seat time and a couple more to get the hot start and cold start right.

With my 8 stack - there's no choke -- but it starts immediately and purrs like a kitten even in very cold weather!

[camcojb]

Originally Posted by GregWeld

Excellent response Jody -- and you're spot on. I've warned many friends that EFI is not for the faint of heart... and that dyno tuning is fun and gets the big stuff out of the way... it can take days of seat time and a couple more to get the hot start and cold start right.

With my 8 stack - there's no choke -- but it starts immediately and purrs like a kitten even in very cold weather!

thanks Greg. And that's why it's important in my opinion that the end-user knows at least the basics of tuning his system. The dyno guy/tuner can get the car up and running, do some dyno pulls as you say, but then it will take a fair amount of time to get the little things all dialed. Who's in the car more, you or the tuner guy? You drive it every day so it really behooves you to know how to tweak the starting, after start corrections, part throttle driveability, etc. as you're the one in the car all the time. He only got the car for a few hours at best.

Jody

[64duece]

Aeromotive offers a one way check valve that will screw directly into the pump to maintain system pressure. PN15107 is the 10AN version. As stated, slow starts can be combined with a combination of system prime, minimum iac or throttle plate position and cranking fuel/timing.

Most of my customers usually start with a full day of tuning and we try to minimize our dyno time and usually can get the WOT stuff sorted out in less than half a day on a NA application. We try to spend as much time with hot/cold idle, transient and cruise driving. Trying to teach the end user as much as we can. We generally refer to it as a "tuning/training session" for those that are more hands on.

[jjump59]

Thanks for the replies, I understand the problem is probably going to be cold start stuff and it's something i'll have to figure out. drove car twice over the weekend (short trips around the neighborhood). thing runs great, even better then I thought it would. 1st time out when I shut off it would not start again until it cooled off, cranked fine but no fire. After it sat for a couple of hours it fired right up. 2nd time it fired right up and ran good, I didn't try to start it when done so don't know what it would have done. Any suggestions on where to start with the cold start tuning?

[GregWeld]

Seriously --- there are SO MANY things in tuning an EFI set up - that there's no way to teach you what to do via a forum like this... as much as many of us would probably like to be able to... it's just impossible.

Cold and Hot start have several parameters to deal with - based on ECT (engine coolant temp). You are either pulling out some fuel or adding some fuel... usually pulling out (leaning out) the cranking fuel when hot -- and adding (richening or fattening) fuel when cold....

I would let the car sit overnight - then without starting - turn the key on and open your laptop to the screen that shows you the cold start enrichment... I can't tell you what that screen is actually - they all label these screens with different names and I use Accel Gen 7... but somewhere in there is a screen that will show you ECT and FUELING.... again without knowing your particular program I can't tell you if you're bumping via a percentage or what - but I'd try adding some fuel if it is a little cold starting... maybe bump it up 10 or 15%.... don't do much -- see if it will start - if it starts faster -- GOOD you're on the right track - if it doesn't start - then try pulling some fuel OUT -- and see if that gets any better.... I would only do this for the TEMP that you are in at that very moment (ECT scale will show you exactly where you're at - only adjust it right there - don't mess with the entire scale - at this point you're just fishing!)

For the Hot start --- do the same thing -- get motor warm -- hook up the trusty laptop and see the warm start fueling screen (most likely the same screen as cold -- just on the upper scale TEMPERATURE WISE) -- try pulling some fuel out - see if it starts better - if not ADD some fuel...

Once you kind of see where you're add with this - then you might try smoothing the fuel curve out -- so that you're affecting a little wider area on the ECT scale of things....

Hope this helps....

SO here's the deal -- it could also be a timing issue..... you may need to adjust timing either up or down just for COLD START and or HOT START... but I'd mess with the fueling first to see if that helps before I'd mess with the timing. One thing you'll learn with EFI tuning -- only adjust and work on one area at a time -- otherwise --- you won't really know what adjustment you did that made the difference... if you mess with fuel and timing --- which was it that changed? Get my drift?

Lean for a day - Rich for life!

[BBC69Camaro]

Originally Posted by 64duece

We try to spend as much time with hot/cold idle, transient and cruise driving. Trying to teach the end user as much as we can. We generally refer to it as a "tuning/training session" for those that are more hands on.

I got find a tuner out in Southern California that offers something like that, sounds great.

[jjump59]

Great info, I understand where your coming from on the only change one thing at a time. We race dirt late models and have the same mantra there. I'll hopefully be able to mess with it some this weekend. thanks again! Jeff