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Old 03-17-2013, 09:05 AM
Mark rsa2au's Avatar
Mark rsa2au Mark rsa2au is offline
TT Enthusiast
Join Date: Mar 2013
Boat: Mastercraft X5 2001. 310hp preditor
Location: Australia
Posts: 178
Indmar 310 TBI running rich, rough and backfiring

Hi Guys, First post but been checking out this forum for a few months researching my next boat which I now have. A 2001 Mastercraft X5 with the 310hp TBI Indmar Preditor engine and 270 hours. It has stood for 2 years with very little run time. I live in Melbourne Australia and the local MC dealer is EXTREEMLY UNHELPFULL because I did not by my boat from them, so I do not have access to MC specific diagnostic equipment.

The engine is not very happy and last weekend used a full tank (30 Gallons) in about 2 1/2 hours. It also cuts out, runs rough and surges on half throttle. When you floor it, it pings a little on occasion but not always. After the work below it now seems to run better but with timing advanced it pings heavily on pull off and starts to back fire at about 4400rpm, then retarding the timing - no ping but backfiring at 4100. Then sometimes we will have no ping on pull off and no backfiring at 4500rpm. Max WOT seems to be 4500rpm on the origional prop. It also runs on a little after a full throttle run and shutting off after a short idle.

Initialy it was running so rich it looks like a diesel engine with the black smoke. The injectors were also sticking in full open position even with the wires removed so obviously new injectors were installed. Fuel pressure measures about 25 to 30. Plugs are new, fuel is fresh.

Next we tested and then replaced the MAF sensor with a little improvement. Temp sensor is also giving the right readings, as is the throttle position sensor. Today we noticed the idle adjusting motor was not opening / closing as it has a lumpy idle but it idles nevertheless.
Disconecting the temp sensor kills the motor, but removing the maf sensor, and the TPS does nothing and the boat runs ok with out them.

Finally after 3 weeks and 15 hour runtime (7 tanks of fuel) we have less smoke, the plugs are a tan color, and the idle is still lumpy untill we replace the above mensioned sensor / motor but it still is not what I expect.

Can any one shed any light please on what to do next to reduce the ping but stop the backfiring at high throttle openings.
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