Z302

Could faulty timing from the initial installation be the cause of this much of a loss of RPM?

VetteLT193

possibly. could also be engine alignment.... maybe bad fuel? did you get all the old gas out of there and change the fuel filters?

stupid question, but is the throttle body moving all the way open?

You are using a complete 502 MPI setup correct? meaning you didn't put the 454 intake and injectors on top of a 502?

new air filter? or is it at least clean?
Any black stuff in the engine compartment? odd smells?
Did the gimbal bearing get checked on installation?
Does the engine rev over 4000 in neutral? (the no load test)
Are the accessories new or old? any issues with the belt?

Basically... go through everything one time to make sure nothing is binding, tough to spin, everything is opening / closing properly and the engine is getting fuel and air.

DLEWIS1340

Any new development here?

Z302

Sorry about the lack of response on this but there has been some new developments.

Reason for loss of WOT RPM was mostly due to improper initial timing of the motor. After realizing that the timing was not set properly because the motor was never put in base timing mode when timed to 8* BTDC.

Problem now is the motor seems to not be firing on all cylinders as noted by the RPM's jumping 200-400 when running. I decided to pull the manifold and check the injectors and found one of them did not open when 9v is applied to it. I am searching for a replacement and will update when I reinstall injectors. I am fearing that I will be pulling the motor soon and have it gone through. I have found a local machine shop in Jacksonville (Precision Machine) that will go through the engine, perform the machine work needed and reassemble for around $900 minus parts. I am looking at possibly purchasing the rotating assembly from ATECO that is listed here on the classified section and just doing it so I know where I stand with this 502.

Any suggestions?

Z302

**UPDATE** Thank you all for your help in narrowing down my engine issues.

After replacing the faulty injector ($125) and correctly setting the timing to 8BTDC the engine has come to life. I took the boat out this weekend and it idles smoothly and is very responsive in the entire rpm range. My WOT is going to be over 5000 due to the smaller 22P props I installed thinking that was one of my original problems. I am going to go back to the factory 26P this week and see where my WOT falls and I even have a set of 28P if it still is too high. At 3/4 throttle with the 22P had the tach right around 5000-5200 and the motor still had alot more to give so I am hoping maybe the 26's will put me in the 4800 range as I feel that is where my WOT should be for my 502 Mag Mpi. I think the range is 4600-5000 if I am not mistaken. My Mariah is not going to win any races but is a great boat for my young boys and still have lots of room for several adults with the ability to have the cuddy for when the weather turns, which is does almost everyday at 3:30 here in Florida.

Next step is to add the additional 2 JL Audio Marine 10" subwoofers I recently purchased to finish out my system (see below) and finally enjoy the boat during the next couple of great boating months here in NE Florida.

Secondary source of power:
Clarion CDM5
Sirius Satellite
Rockford Fosgate Power T8004 4 channel amplifier
Rockford Fosgate Power BD1000 mono amplifier
3 pair JL Audio M770-CCS Component speakers
3 pair Skylon Rubicon 6 1/2 coaxial speaker (will be replaced with JL's)
3 JL Audio M10IB5 Subwoofers