Need some help with 502 Problem
 

Recently, I performed an arizona speed upgrade on my 1998 502 efi motors, new dart heads, cam, rockers, msd ignition computer remapping,cmi exhaust etc. in theory they should be running close to 500hp at the prop.


here is the problem that I need help with:

my port motor backfires at idle but the timing is set perfect and all clearly obvious reasons for the backfiring have been checked. the motor runs 400 rpm less that starboard at wot and the performance of the boat is 4 mph less than stock before i performed the upgrade.

the boat is proped to run 5200 rpm wot .

oh by the way the boat is a 1998 35 fountain

any advise at this point would be great.

Re: Need some help with 502 Problem
 

Im dealing with a similar prob, my fuel pressure regulator was coroded and was showing 90 psi fuel pressure, after repair back to 41,

Re: Need some help with 502 Problem
 

maybe you have a bad injector-did you do a cylinder drop test?-

Re: Need some help with 502 Problem
 

wouldnt the bad injector come up as a code on the ddt

Re: Need some help with 502 Problem
 

no... as long as the pulse is present, there will be no code. you might want to look at something REALLY simple like the firing order... it is really easy to get the wires mixed up on the cap and and will give you that idle backfire yet SEEM to run sort of ok...

did these things run on the dyno when complete ?

Re: Need some help with 502 Problem
 

Have you rechecked the valve lash?????

I would do a leak down to rule out a valve that is sticking open.

Re: Need some help with 502 Problem
 

There was no dyno time. I will perform the leak down test and see about a valve. as far as spark plug wires go they are all in the right spot, double and triple checked.

one other idea is, az speed did the computers, could one of the computers not have been flashed correctly?

Re: Need some help with 502 Problem
 

Try to swap ecu's between your 2 engines. If the problem follows the ecu, you got the problem found. If not, get into checking the motor.

Re: Need some help with 502 Problem
 

the reason why i post this question is this:

prior to the motor upgrade the motors were stock 502 mpi, the boat ran 72mph at wot with bad compression ot of the port motor spinning 26 hydromotives non labbed @5100 rpm. obviously we all look for more speed so an upgrade was performed instead of a valve job.

here is where my performance numbers are at now after the 20k upgrade

5000 rpm starboard
4600 rpm post this is the backfiring motor

68mph wot spinning the same props before the upgrade

Is the port motor causing me to lose this much speed, i was thinking i was going to gain 10 mph with the upgrade not lose 4.

az speed told me the motors should now be producing 520 at the crank and about 500 at the prop. comparing this to 35 lightnings model year 96-99 running 500 hp they perform 80 to 82mph

some thing is wrong here?

Re: Need some help with 502 Problem
 

Sounds about how mine ran with a rounded cam lobe.

Re: Need some help with 502 Problem
 

an injector wouldnt present a code on any scan tool

Re: Need some help with 502 Problem
 

I had the injector problem too, threw no codes and at 85 hours

Re: Need some help with 502 Problem
 

I will swap computers on monday, if thats not it i will check everything else mentioned above and post findings later.


thanks alot guys

Re: Need some help with 502 Problem
 

well... first... 10 more mph is going to require about an additional 200 - 225 hp PER engine at that speed....

second... whoever suggested swapping the ecus is spot on...that gives you a quick answer right off... and the same goes for the rest of the sensor array

it sounds to me like a warrantee issue for arizona speed. also... if i read your post correctly you said you were looking for 500 hp... didn't those motors make 425 to start ? soo all this work for 75 hp / side ? sounds like a not great deal to me...

Re: Need some help with 502 Problem
 

how much faster do you thnk that boat will be with an additonal 100 HP per side?

Re: Need some help with 502 Problem
 

I agree that a failed injector(s) will not set a trouble code, but did you check for trouble codes? I also agree that swapping the ECM's would be a good place to start.

While you are troubleshooting, I would disconnect the MSD boxs, recheck the timing and run without them until you find the problem. It's all about eliminating possible causes.

Dave

Re: Need some help with 502 Problem
 

we had this discussion the other day and someone found a pretty good calculator on a site somewhere. i use the math.

HP = drag x V cubed ( in ft per sec)

you say you had 72 mph w/ stock 502's so about 850 hp

so back into your drag number... 850/ 1177583 = .00072

so

hp = .00072 x 1715932 ( 82 mph cubed in fps) = 1235 hp or another 385 hp total...

am sure the online calculator will give you a similar number

1050 hp should give you about 5 mph give or take

Re: Need some help with 502 Problem
 

during some troubleshooting, a map sensor code came up on the ddt, i will be replacing the sensor, can this be the total problem?

Re: Need some help with 502 Problem
 

the injectors are all working correctly 46psi

Re: Need some help with 502 Problem
 

just exchange maps sensors between motors. also... don't understand your comment about "injectors working 46 psi " pressure and actual electrical injector function unrelated.

Re: Need some help with 502 Problem
 

talking about fuel pressure

Re: Need some help with 502 Problem
 

Is the backfire steady under a load or does it just do it at idle, it sounds to me like a lobe off the cam, or plug wires 5and 7 are switched around. How were the cams broken in. Ed

Re: Need some help with 502 Problem
 

just at idle, the backfire goes away under load but the motor lags bigtime underload throughout the whole power curve and is apprx 500 rpm off at wot. the cams home less than 2 hours on them and the backfire started upon first start, this should rule out a rounded lobe.

Re: Need some help with 502 Problem
 

Then I am back to the wires being wrong or maybe a mis adjusted valve....I have seen a lobe round off on a cam in less than twenty minutes of running time with to much spring pressure and not enough assembly lube or improper assembly.....Ed

Re: Need some help with 502 Problem
 

yes, i agree. but i saw the cams go in a they were lubed well. valves were torked to specs I watched each one done.
wires are all in the right locations. i really do not want to pull the motor again. what is the best test to see about an mis adjusted valve, my engine compartment is perfect you can eat off the floor dont want too much mess.

Re: Need some help with 502 Problem
 

If it started upon initial start up, I would think it is a valve not fully closing or leaking---rocker arms adjusted too tight maybe.

Re: Need some help with 502 Problem
 

What do you mean by "torqued to specs"??????

They should not be torqued unless it is a stock cam with the stock rockers and bolts.

Everything you describe sounds like the valves are too tight.

Re: Need some help with 502 Problem
 

I would have thought this a roller cam, but if you are concerned about a lobe going away, chisel open the oil filter and check for metal.

Is it popping out the exhaust or intake side?

BT :cool:

Re: Need some help with 502 Problem
 

it is a crane cam and crane roller rockers dart heads

Re: Need some help with 502 Problem
 

A leak-down test is probably the leest messy, and would tell you exactly which cylinder and which valve or valves. pulling the valve covers and checking the adjustments is messy and time consumming but equally as effective. Griff is right valves donot get torqued they get adjusted to zero lash and then somewhere between 1/4 and 1 turn down to center the lifter piston in its bore. Ed

Re: Need some help with 502 Problem
 

I had the exact same work done by ASM several years ago and only picked up 4 mph. Didn't think this was too good, so I'm heading in a different direction.

Re: Need some help with 502 Problem
 

If you still don't find it....MSD has a good troubleshooting section on their Ignition systems.

Re: Need some help with 502 Problem
 

Have you checked the fuel pressure all the way up to WOT? .

Re: Need some help with 502 Problem
 

after much troubleshooting the problem was a combination of three things, a map sensor was bad, a pcv valve was stuck open, and i reinstalled all the spark wires and the problem went away. motors are running great but

now brings my next question, iam very unhappy with the performance after the upgrade this is why.

before the upgrade with 1998 tired motors one motor had 90 compression on 2 cylinders the boat ran 72.1 gps full fuel,2 people, spinning 26 hydromotives @5000 rpm wot.

the upgrade was asm, new upgraded crane cam, dart heads, msd ignition, roller rockers, cmi exhaust and a computer reflashing. cost of parts was approx 18,000.00.


heres what the performance is now(it sucks)
between 1/2 and 3/4 fuel,2 people, 26 hydromotives compression is back to 150+ on all cylinders. boat ran 74.4 gps @5000 rpm
water and wind were the same before and after.

the only thing i did not do was change the intake to get more air into the motor. do you guys think this is hindering the new heads and cam from working properly ie creating more hp?

Re: Need some help with 502 Problem
 

I don't think the intake is what is causing the HP loss. Tyler Crocket does a simmilar upgrade to the factory MPI motors. He gets 100HP more a side by the same means you have went with, only with different components.