Advice on MPI's fuel systems
09-17-2002, 04:50 PM
#21
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DonMan,
actually I did see a fuel economy increase from a base 300hp 454 to a full-roller 454 -450hp block with Procharger and Nickerson flowed carb. AWESOME combo and never broke anything!!
The economy increased in cruise and in planing performance. WOT was where ya' would lose it!! This was on a '93 252SS Formula.... not a light boat!!
I tend to agree with the ECU/ECM-EFI problem....but that goes for us know-nothings that do not have the knowledge or the TIME (most of all) to really learn some of this stuff. We are more comfortible with carb's because we feel we know them. And in many ways a carb is better/easier....you cannot lean out one cylinder and melt one piston with a carb getting stopped up, the entire engine lays down....... you really can't feel it or hear it in a twin eng config. until it's too late ( my experience this summer). Now mine is fixed and still EFI. If more problems arise, I too will probably do the carb thing even though I don't want to..
actually I did see a fuel economy increase from a base 300hp 454 to a full-roller 454 -450hp block with Procharger and Nickerson flowed carb. AWESOME combo and never broke anything!!
The economy increased in cruise and in planing performance. WOT was where ya' would lose it!! This was on a '93 252SS Formula.... not a light boat!!
I tend to agree with the ECU/ECM-EFI problem....but that goes for us know-nothings that do not have the knowledge or the TIME (most of all) to really learn some of this stuff. We are more comfortible with carb's because we feel we know them. And in many ways a carb is better/easier....you cannot lean out one cylinder and melt one piston with a carb getting stopped up, the entire engine lays down....... you really can't feel it or hear it in a twin eng config. until it's too late ( my experience this summer). Now mine is fixed and still EFI. If more problems arise, I too will probably do the carb thing even though I don't want to..
09-17-2002, 05:52 PM
#22
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Jdelo- Not really familiar with the FAST system, but I'll assume it's sequential [or batch],a little more tuning resolution,and still a "speed density" type control system...No ego here, but I think it's the "tuned" OEM runners that make it hard to deviate from the intended use. Also, did anyone experience any seat of the pants diffrence when they went from a MEFI-1 to aMEFI-3?....In the real world, it's probably not discernable...my point is, while the MEFI3 was in controller terms apretty nice improvement, it still wasa micro improvement...this is the way we will feel about the new sequentials coming to us now...another micro improvement...they do add up over the years ,though. Put the FAST system on a suitable [for your RPM and hp range] manifold and I'll bet it's pretty sweet.
09-17-2002, 06:41 PM
#23
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Liquid Lounge,
FAST is just one of the aftermarket fuel management systems available. HALTECH,HOLLEY AND ELECTROMOTIVE are other vendors I've been researching. And yes the FAST can be configured to be Batch or Seq. . The point I'm trying to make is that you yourself can not change or modify and parameters in the MEFI 1 or MEFI 3. The software is just not available. Plus it gets very expensive everytime you make a modification. Add headers , flame arrestor and fuel reg. 350.00 . Make a cam change and head work another 350.00 on and on and on.
Here's another issue getting it right!! The only way to tune the ECU, in my opinion, is in the boat on the water under changing loads. other wise it's just a crap shoot.
JDELO
FAST is just one of the aftermarket fuel management systems available. HALTECH,HOLLEY AND ELECTROMOTIVE are other vendors I've been researching. And yes the FAST can be configured to be Batch or Seq. . The point I'm trying to make is that you yourself can not change or modify and parameters in the MEFI 1 or MEFI 3. The software is just not available. Plus it gets very expensive everytime you make a modification. Add headers , flame arrestor and fuel reg. 350.00 . Make a cam change and head work another 350.00 on and on and on.
Here's another issue getting it right!! The only way to tune the ECU, in my opinion, is in the boat on the water under changing loads. other wise it's just a crap shoot.
JDELO
Last edited by jdelo; 09-17-2002 at 06:46 PM.
09-17-2002, 07:39 PM
#24
I hate the winter!!
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This is a question that has been in my mind for a long time. I came very close to do modifications to my motor. After discussing it here on this board, I decided to leave the motor alone. I have been running this boat for 2 years and so far, I can say that other than upgrading that $*itty stock exhaust, I have not done anything more than change the oil and plugs. As was mentioned above, these injected motors run great at the level that Merc. sets them up for. Anything else and you will be rolling the dice as to how long it WILL take for a meltdown. Personally, I would rather run the boat every weekend than be pulling the motor out every other weekend to drop in new pistons.
The way I decided to get a little more power for next season is to look for a used HP500EFI to drop in.
The way I decided to get a little more power for next season is to look for a used HP500EFI to drop in.
09-18-2002, 01:31 AM
#25
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Blown Formula,
While I agree that moving the regulator as close as possible to the fuel rail will help reduce the bounce you are talking about I think you may be overlooking the cause. The bounce is caused by insufficient line/rail volume after the regulator. The injectors are draining all of the supply and pressure from the rails. When you see the bounce what is actually happening is fuel is rushing back to fill the empty rails. Moving the regulator as close as possible reduces the bounce by giving the fuel less distance (volume) to fill suddenly. This occurs most often in batch fire EFI but I have seen it happen quite a bit in SEFI as well. No matter what volume or pressure pump you are using if the fuel rails cant hold sufficient volume you will still see this happen. The gauge might not show a bounce but it is still happening. The rails need to hold a reserve or you run a lean condition. This isn’t new to me at all since I dealt with it years ago when building high hp EFI fords. We put bigger pumps in the cars, bigger injectors, and moved the regulator right onto the rail. Guess what? The gauge stopped bouncing but we still were toasting pistons. This was on a sequential system requiring only 8 42lb/hr injectors. The problem was solved when we changed to larger fuel rails and installed larger lines from the regulator to the rail. In fact we ended up with an overly rich condition. If you already lost an engine due to insufficient volume and think that moving the regulator close means problem solved I would rethink that. It sounds like you have a volume issue with the fuel rails. Do yourself a favor and have the engine hooked to a good air/fuel meter just to make sure. Change out the rails for a larger volume set, make sure all the fittings are as large as possible, and use the largest lines you can after the regulator. – 10 lines usually do the trick.
My 1999 7.4 MPI has the dampener attached to the stock fuel rail. I just went and pulled it off the shelf to make sure. The dampener just compensates for the surge of fuel by cushioning the impact. Its sole purpose is to smooth out pressure irregularities seen in batch fire EFI systems. This reduces shock to the regulators diaphragm and allows it to function properly. My engine currently has a Whipple on it. That kit replaces all of the stock manifold, fuel injectors, and rails. The kit includes 6 higher flowing injectors on a custom rail. It only has 6 injectors total now. The rail provided in the kit is very large volume. The only changes to the stock fuel system are; #1 modifying the stock regulator to an adjustable, #2 the rail and 8 injector to 6 injector swap, #3 setting fuel pressure to 45-50 psi. The kit also uses a Whipple provided dampener which sits on the rail. I NEVER see any pressure bounce no matter what RPM. At WOT I am still running too rich.
Rick,
The 7.4 is a batch fire EFI that fires 4 injectors at a time, left bank then right bank. Modifying the fuel system on one of these is very limited unless you want to yank it out and start from scratch. The cool fuel box integrates the regulator so if you want to move it you need change the pump assembly to a more conventional design. As long as you have a properly functioning pump and don’t exceed the volume limits of the 7.4 common fuel rail you should be fine by using one of ASMs adjuster kits. Most likely you wont need to raise fuel pressure unless you get extreme. The stock system on these engines are usually too rich and reducing pressure works better but I would have the ECU reprogrammed before I messed with fuel pressure. Some little things I did to get a little more punch before I supercharged really helped. First throw away the stock flame arrestor and get a K&N, while you are in there trim the throttlebody gasket so that the passage is no longer blocked. This makes the intake air a little noisier but you probably wont hear it with the hatch closed. You should notice better acceleration after doing this. Make sure your base timing is set properly; I found that my engine was based at 4 degrees when I checked. I am pretty sure its supposed to be set to 10 degrees (the whipple requires 10 base). Open up the exhaust, with mine I still use the stock manifolds but I replaced the tips with a free flow un-muffled set and picked up 3 mph(before putting on the blower). A set of headers should do more for you but then you start spending more. I plan on keeping the stock headers(manifolds) until they rust out. With the blower I am already 22mph faster than I was stock (with room to go) and better headers don’t seem that necessary now
While I agree that moving the regulator as close as possible to the fuel rail will help reduce the bounce you are talking about I think you may be overlooking the cause. The bounce is caused by insufficient line/rail volume after the regulator. The injectors are draining all of the supply and pressure from the rails. When you see the bounce what is actually happening is fuel is rushing back to fill the empty rails. Moving the regulator as close as possible reduces the bounce by giving the fuel less distance (volume) to fill suddenly. This occurs most often in batch fire EFI but I have seen it happen quite a bit in SEFI as well. No matter what volume or pressure pump you are using if the fuel rails cant hold sufficient volume you will still see this happen. The gauge might not show a bounce but it is still happening. The rails need to hold a reserve or you run a lean condition. This isn’t new to me at all since I dealt with it years ago when building high hp EFI fords. We put bigger pumps in the cars, bigger injectors, and moved the regulator right onto the rail. Guess what? The gauge stopped bouncing but we still were toasting pistons. This was on a sequential system requiring only 8 42lb/hr injectors. The problem was solved when we changed to larger fuel rails and installed larger lines from the regulator to the rail. In fact we ended up with an overly rich condition. If you already lost an engine due to insufficient volume and think that moving the regulator close means problem solved I would rethink that. It sounds like you have a volume issue with the fuel rails. Do yourself a favor and have the engine hooked to a good air/fuel meter just to make sure. Change out the rails for a larger volume set, make sure all the fittings are as large as possible, and use the largest lines you can after the regulator. – 10 lines usually do the trick.
My 1999 7.4 MPI has the dampener attached to the stock fuel rail. I just went and pulled it off the shelf to make sure. The dampener just compensates for the surge of fuel by cushioning the impact. Its sole purpose is to smooth out pressure irregularities seen in batch fire EFI systems. This reduces shock to the regulators diaphragm and allows it to function properly. My engine currently has a Whipple on it. That kit replaces all of the stock manifold, fuel injectors, and rails. The kit includes 6 higher flowing injectors on a custom rail. It only has 6 injectors total now. The rail provided in the kit is very large volume. The only changes to the stock fuel system are; #1 modifying the stock regulator to an adjustable, #2 the rail and 8 injector to 6 injector swap, #3 setting fuel pressure to 45-50 psi. The kit also uses a Whipple provided dampener which sits on the rail. I NEVER see any pressure bounce no matter what RPM. At WOT I am still running too rich.
Rick,
The 7.4 is a batch fire EFI that fires 4 injectors at a time, left bank then right bank. Modifying the fuel system on one of these is very limited unless you want to yank it out and start from scratch. The cool fuel box integrates the regulator so if you want to move it you need change the pump assembly to a more conventional design. As long as you have a properly functioning pump and don’t exceed the volume limits of the 7.4 common fuel rail you should be fine by using one of ASMs adjuster kits. Most likely you wont need to raise fuel pressure unless you get extreme. The stock system on these engines are usually too rich and reducing pressure works better but I would have the ECU reprogrammed before I messed with fuel pressure. Some little things I did to get a little more punch before I supercharged really helped. First throw away the stock flame arrestor and get a K&N, while you are in there trim the throttlebody gasket so that the passage is no longer blocked. This makes the intake air a little noisier but you probably wont hear it with the hatch closed. You should notice better acceleration after doing this. Make sure your base timing is set properly; I found that my engine was based at 4 degrees when I checked. I am pretty sure its supposed to be set to 10 degrees (the whipple requires 10 base). Open up the exhaust, with mine I still use the stock manifolds but I replaced the tips with a free flow un-muffled set and picked up 3 mph(before putting on the blower). A set of headers should do more for you but then you start spending more. I plan on keeping the stock headers(manifolds) until they rust out. With the blower I am already 22mph faster than I was stock (with room to go) and better headers don’t seem that necessary now
Last edited by NineLives; 09-18-2002 at 01:38 AM.
09-18-2002, 02:58 AM
#26
I'm with JDELO, 'the only way to check is in the boat on the water'. But you need proper instruments. Wide band O2 sensor and readout at minimum. That is why I'm working on the On-Board-Dyno so that with the adjustable ECU's you can change the timing and injector pulse width at different rpm's to get the max Torque. Or also with a carb to adjust the jets.
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