502 mpi guardian issues!!

Revrider313

Recruit
Joined
Oct 3, 2017
Messages
1
Good day.

I have a 99 zx22 donzi with a 454 of throttle body injected motor in it. I wanted to get more out of it so I got a set of big rec port heads, 502 mpi harness/ecu, cam, roller rockers, and all of the other fixins. With diacom hooked up, it shows no knock sensor ever active. The boat is quite doggy coming out of the water and then all of a sudden it just takes right off. But then immediately falls on its face. When you bring the throttle back to idle and start again...it will get up on plane and do it all over again. I was then watching the scan tool closely while driving and it seems like when the boat take off that when it really starts to get timing. And when it falls on its face that's is when it has all the timing taken away. Makes sense...losing 16* timing will do that. I also learned this is basically limp mode.
Yes timing is good and done in bad timing mode. I have had the thing from one side of the spectrum to the other. Fuel pressure is 43.5psi coolfuel.
When I key on I get 2 simultaneous codes. Tps voltage high and coolant temp sensor. They can be cleared while driving but just come back with restart. Both sensors are working on the scanner though!
Please help!

Thanks
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
You have a 454 and replaced the heads with 502 heads, and are using the 502 ECM?
If the ECM has not been reflashed there will be performance issues. The TB injectors may not flow enough fuel, Need to check with Air Fuel Ratio meter

Tps voltage high and coolant temp sensor. They can be cleared while driving but just come back with restart

Clearing the codes while running only clears from being displayed but if they are actually still there (sounds like they are) the ECM will retard timing. The MEFI-3 ECM does not have much resolution when it comes to diagnostics. ECT and TPS high can be from an open circuit
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Good point from AD above.
That said. Tps and IAC likely culprits.
 
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