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454 mag won't rev over 4k - fuel pressure?

You need to get your engine hooked up to a Diacom it is the only way you will be able to pin point the problem, Find a shop that has a diacom diagnostic computer. trial and error of replacing parts can be far more expensive. the fuel pressure and compression test go along with it and you already have done that.

Good luck with finding the problem
 
any word on the outcome? I got a 454 mag mpi thats driving me a bit crazy on the wot too, no lean pop for me though, I just cant seem to get the thing past 4200 rpm without practically putting the drive into trailer position (and for those of you that think it needs allot of trim the prop is clearly out of the water as i lose speed).
 
Update and Progress....

After a week or so of sitting in our flow lab, I pull the injectors and send them to Witch Hunter performance injector service in Washington State (I highly recommend them). The guy at WH calls me and says 2 of my injectors were 60% clogged. But he got them all clean and working fine. He and the my FI buddies at Bosch say that the old style injectors are bullet proof, but they can clog.

The pisser is that in 1998, Bosch won the whole fuel system for the GM marine motors. If my motor was 3 years newer, I could have all new parts for a few cases of beer!

I should know for sure tomorrow if that was it. Between the high fuel pressure and the clogged injectors, some cylinders were probably running rich and some lean. Who knows what the heck the ECU was trying to do with the high pressure. My buddy say the merc. diag. tool said the ECU was sending funky pulse widths to the injectors - probably as a result of the high fuel pressure.

Brian - holy cow, I hope I don't have a cam timing issue. Plus the MDT showed the spark timing to be OK - hopefully that's not it!

Baja252 (rough name for this site, but all are welcome!) - based on what I've learned from mine: Check compression, vacuum (should be steady) and fuel pressure. All easy enough to do with a shop manual and $80 worth of gauges from autozone. What do your plugs look like? Like MK says - get it hooked up to a diacom / MDT - that will tell you alot. My $0.02 says you have clogged injectors, but it could be a bunch of things. Your injectors may all be clogged more evenly than mine. I think I got the pop because of the 2 being so lean/clogged. Thank goodness I didn't run it much (or hard) like that.

Oh, I'm going to be a big azz on that little lake near my house if he boat runs. 65 mph up - 65 mph down - 65 mph up. Maybe I'll put the 25p on and head up to the saginaw this weekend! Only upside is I just missed one boating weekend and we went out on my buddies big 25' deck boat that weekend.
 
Another update. My buddy calls me and said right before he put the injectors in, he figured he should look inside the VST tank. He said it was UNBELIEVABLE what was in there. The strainer looked like it was 100% clogged with a dirt and a gel like substance. It was the first time the VST had been apart. Problem is the O-ring that seals the top half on has expanded by about 1/4" and they are on backorder. It's a shaped o-ring / seal so we need to find the actual piece - or maybe make one.

Anyhow - it sounds like anyone with an MPI motor should take a peek inside of their VST tank. The fuel filter that came on the boat was squeaky clean - so there weren't any obvious signs...

Boat will be back together as soon as we find that seal!
 
Yeah, the name might not be the best, I should have gone for "454 mag mpi", but thanks for the welcome! I will have to take a look at the injectors next, maybe back flow them to clean them out, I heard thats a method. I had the engine rebuilt with 30 over forged higher dome pistons (compression about 9.4:1) and got new heads for it (same casting numbers but in better conditon, with newer valves and springs, so the engine is fresh to say the least, I got about 180 psi per cylinder.......yes, I run higher than 87 octane! I also dont have the vst set up but rather the fuel cooler, bigger pump, and adjustable regulator, with a guage (the motor once had a blower.....before the rebuild). I run about 40 psi of fuel pressure according to the gauge, which is higher than stock of 37 I think, but my plugs are supper tan almost whitish, which screams lean, and heres the kicker, I was soo paranoid about burning something up, I jacked the pressure up to 60 psi and they were still the same! So maybe I do have clogged injectors, but Ill tell you what, they are all clogged if its the case. To make matters more complicated, I checked the trouble codes when I first put it together about 15 hours ago and got no codes, then the thing started running funny about 14 hours in, not idling out of the channel well, like it wanted to stall, but having power and revving when revved, and i got a code 14 or temp sensor code when i checked, so yesterday I changed out the sensor and have yet to run it, so maybe it had a bad sensor that was giving a low or high reading but not enough to trip a code......until recently. But according to the manual the resistance of the sensor at room temp is right, and pretty close when i put it in a glass of ice. So this just adds another layer of complexity to the whole thing, so far the record is 4500 rpm.......i dont run it there for more than a minute or 2, I would think this thing should be maxing out at 5k, never mind not even hitting 4600 which is the low end of the range....I freind of mine has a buddy with a marina and all the merc tools that hopefully will do me a favor and scan the computer, not sure what else besides codes he can get or do but Ill at least get a second opinion.... to be continued....
 
Hi Baja,

I'm by NO means an expert, but your issues sound exactly like mine. -- Send the injectors to witchhunter! Now! Maybe check out your fuel system back from the rail where you can see it first. But my $ is on clogged injectors and probably gunk between there and back towards your fuel filter too.

Also 60psi sounds real high 33 is the nominal spec. - you're risking banging up your injectors and maybe running some of them rich. My adj. regulator went bad and gradually increased FP - the higher it went, the worse my boat ran! In the end it was running 60psi. My tech buddy said that was not what you wanted. Somehow I think higher pressures might free up gunk and clog your injectors faster.

My plugs all looked the same - perfect tan cardboard colored. Don't try to clean them yourself, they're $200 each from Merc and the cheapest mallory aftermarket price was $140 each. So you're messing with $1100 worth of injectors there, and you won't ever know what you had or what you have - plus there are some screens in there that look fragile. WH puts on new o-rings and seals which is another bonus. Witch hunter is $19 per injector, plus $10 total ground shipping back. Turnaround time is 2 days. I don't work for them, I just think they provide a great service at a pretty crazy cheap price. I paid airfreight both ways and had my injectors back in 4 days.

Also check your fuel system for gunk. You have to have an electric fuel pump somewhere so go through all of that. I suspect my mechanical "supply" pump has something going away in it that helped clog everything up. I need to still run that down.

As mentioned earlier in this thread, I work for Bosch - makers of the original pintle type injector (EV1) that's in our motors. Our Rochester (Delphi) injectors are straight knock-off's of EV1's. I surveyed about half of the injector design group and found that Pintle's are pretty bulletproof, but they do clog.

The good Mr. Hammer informed me that that those motors have a soft rev limiter around 4900 rpm +/- maybe 100rpm. Mine revs to an indicated 4900 rpm on my in-dash tach with my 23p unless I'm really loaded.

Hope this helps.
 
hmm, well, i had the opportunity to buy a whole intake with injectors and rail fro this motor for less than 200 and I just did. Ill swap out the injectors and see if there is a change, this intake is a few years newer and the engine ran perfectly im told........I have a hard time believing they are all clogged. Worse case I figure I should be able to resell the intake and injectors for at least what I paid.........seeing as they are soo expensive brand new. i hope its the injectors. Ill post again with outcome.
 
It's ALIVE!!!

I got it back in time for last weekend. Ran a bit stronger up and out of the hole and nice and smooth. Pulled the same healthy 4900 rpm as when it was running well, seemed to get there a bit quicker - that equated to only 64 mph heading into a solid 18" chop on Burt lake but I didn't really wring it out and I'm sure the headwind had something to do with the missing 1.5mph. Motor felt nice and strong. I need to try out my 25P mirage next weekend.

Results from which hunter were that only a couple were running at about 60-75%. The rest were better, but not perfect.

Baja - once you get your stuff figured out, I'd appreciate getting first shot at that manifold and injectors. Since I have non-OEM injectors, I'd be real interested in picking up a set of original injectors. They should be Rochester (aka Delphi). As posted earlier - they are pintle style and both my Bosch injector engineers and Witchhunter claim they can get clogged, but never actually go bad.

SO - for the MPI crowd - if you have a VST tank, pop the top and see what's in there. And if it's running bad, check out the injectors - or even send 'em off for cleaning over the winter. $160 well spent.
 
I cant belive with all your FI Buddies at Bosh none of them have enough common sense to know how to shrink a O ring. This is a common problem with any used O ring they swell when removed. Some things can't be read in a book.
:bigthumb:
 
Hmm.. freezer? I've never tried to shrink an o-ring...


I might have to take a look into the vst tank to see what is in there... hearing about all the junk in yours makes me curious.
 
I believe the freezer trick works - freezing a bearing (or shaft) makes a big difference.

But this o-ring was the seal on the VST tank - odd shaped and very long, so maybe O-ring wasn't the right term.

In any case, I'm going to pop that 25P mirage on there and see what happens this weekend on torch. Boat seems to push that 23p to redline pretty easily. We'll see what happens...
 
I see what big red is saying, just cool it down and get the rubber to contract so it slips together easier. I def had issues with the orings on my injectors last night and them falling off the grove and leaking, after a lot of poking with a small flat head screw driver I was able to get it all together leak free though with out freezing.
So I made a crude injector test bench with some fuel line, my air compressor and a battery and long story short replaced the 3 lowest flowing injectors from the motor with the 3 highest flowing from the set i bought. The boat def runs allot better, starting almost immediately which surprised me (would take maybe 4 or 5 seconds of cranking to go before, now like 2 or something), and having great throttle response, the wot hasn't changed too much, maybe picked up 100 rpm, so if I push it i can hit about 4800, so thats pretty good, although I would love for it get closer to 5k. I def had an injector issue as running injector cleaner through the motor before I replaced the 3 injectors seemed to have gotten me more rpm, i couldn't go over 4500 before, and all the plugs were whitish. The way I have been going about it is by looking at the plugs to judge the mixture, after the fuel additive 4 plugs were really nice while 4 had all kinds of crap stuck to them, looked like ash, but some was melted, like a glossy yellowish coating on the insulator and tip. So I figured these cylinders were running lean and sure enough, after replacing the 3 injectors they are nice, although one is still off. I am going to run more injector cleaner through it in hopes it gets better (the "off" plug is one of the cylinders with the replaced injector, so maybe it will clear up like the originals. If not, I am going to take it apart again and send them off to witch hunter, but im really really close I think. I will def. keep you mind needafunboat when I decide to unload the injectors.
 
on some of the stingrays boats, theys use a one-way check vlave on the fuel pick up. you have to remove the hose and then barb on the pick. removed mine on my stingray and put a straight thru one on, runs great now. also there is a fuel filter in the carb if it still has a rochester carb on it. found the answer from triple digits.
 
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