7.4 MPI very sluggish

[Ebay Ed]

i have a 1998 7.4 MPI that is a turd out of the hole takes forever to get on plane had a computer hooked up to it tonight and at wide open throttle the timing advance is only 15 degrees total if i ease into the throttle the advance will go up to 26 degrees total but after a certain point it drops to 15 the engine only has 200 hours on it i have changed computers, throttle bodys with the iac and tps, and distributors and nothing seems to make a difference base timing is set at 8 degrees BTDC it does not miss and there are no codes i lost about 10 mph from the old engine ( which i blew up ) to this one and i am pretty sure i will get that back once i get it running right anyone have any ideas ?? thanks Ed

 

[MOBILEMERCMAN]

Does yours have a vapor canister or fuel cooler?

You could be losing fuel flow

 

[Ebay Ed]

yes it does have the cool fuel tube that the electric fuel pump goes into but i dont think it has a vapor cannister and i did not check the fuel pressure as it just didnt seem like it was fuel related and it ran fine with the old engine this all started after i had to change the engine

 

[Ebay Ed]

it only seems to be sluggish under a load seems to rev fine when not in gear

 

[WOTW2E]

Jim,
The DDT is showing 15degrees advance while under a hard load. At wot 4400 rpm and 15 degrees advance. Shouldn't that be 30 to 32 degrees of advance? It has to be a timing issue right? As Ed said, under light load at maybe 1/4 throttle, the advance number will jump around and get as high as 24 or 25 but as soon at you open the throttle under load is goes to 15.
Thanks
Adam

 

[Ebay Ed]

i found this module that is bolted to the back of the engine called a spark advance module but it is not going to be easy to get to to change it kind of wondering what some one elses thought is on this if it could possibly be the problem

 

[MOBILEMERCMAN]

If it is knocking it will retard the timing. I would rule out fuel delivery first. If it was a vapor canister engine I would suspect a clogged high pressure filter. The cool fuel system recirculates thru the separator filter. Since there is no high pressure filter the injectors catch the debris.

When ever I change a fuel injected engine I send out the injectors for service and flow check.

 

[Ebay Ed]

the injectors were on the engine when i bought it used as a complete engine i might just have to park it and have the fuel system gone thru

 

[Ebay Ed]

Jim where would be a good place to send my injectors to and what does it cost thanks Ed

 

[MILD THUNDER]

Sounds like its knocking and the ecu is pulling timing like ed says. If you replaced the engine, due to the last one blowing up, and I would start looking into your fuel delivery system. Clogged filter, anti-siphon valve, etc.

 

[Ebay Ed]

the last one blew up because the timing wasnt set correctly nothing to do with fuel

 

[Ebay Ed]

well i changed the injectors out to the ones from my old engine which ran great until i screwed up and blew it up and also change the fuel / water separator filter anyway the boat ran better friday night ( 2 people ) still had a little bog when i mashed the throttle but it came on plane better / quicker then saturday morning with 4 total people and a cooler could not get it to run any faster than 9.5 mph i was so pissed felt like getting it out in the middle of the bay and pulling the drain plug so i dropped it off at dubberts in port clinton maybe they can figure it out i am tired of dealing with it i have changed everything except for the knock sensors from the old engine and nothing makes a damn bit of difference everytime i change something it goes slower

 

[Ebay Ed]

also checked the fuel pressure this past weekend and it was around 28 key on engine off and 20 at idle and 28 at wot is this right or should it have more pressure on cars and trucks i seem to remember port injection needing to be around 45 + psi

 

[Boat Tech]

also checked the fuel pressure this past weekend and it was around 28 key on engine off and 20 at idle and 28 at wot is this right or should it have more pressure on cars and trucks i seem to remember port injection needing to be around 45 + psi

That pressure is to low.
Do you have your engine serial number?

 

[Ebay Ed]

yes it is L035562 the same engine in my buddies pick up has 56 psi of fuel pressure

 

[Boat Tech]

yes it is L035562 the same engine in my buddies pick up has 56 psi of fuel pressure

Your fuel pressure specifications according to mercruiser service manual #23, is between 34 - 38 PSI, Look for 36 psi to be normal though.:cheers2:

 

[Ebay Ed]

well 15 to 20 psi could be my problem really suprised it even runs Thanks Ed

 

[Ebay Ed]

Dubberts in Port Clinton figured it out it was my fuel pressure regulator that is mounted to the cool fuel they changed it and it runs like it use to with the old engine gets on plane like it should and runs right at 52 mph on the GPS thanks everyone for the suggestions Ed