Starting/stalling Mercruiser 7.4 MPI

[Tntjewell]

Just purchased 2000 Maxum last month with Mercruiser 7.4 MPI. When I start it, it runs for a few seconds then dies. This happens severals times until it finally stays running. Engine runs great, even when idling, its just the start process. If I turn off engine and restart a few minutes later, same process repeats itself. Previous owner showed me receipt that, IAC, fuel pump, shift cable, and water pump assembly was replaced in July. Took it to mechanic, and they feel that the fuel injectors need cleaning or replacement. Any thoughts? Thanx for any response. Also, the mechanic says 3-4 hrs labor, $125 per injector to clean, or $300 per to replace. That seems kind of steep.

 

[Bt Doctur]

3-4 hours, .................. I dont think so
how about $17.00 to clean and you remove them ? More like $140.00 for a new set.
pm me for info

 

[alldodge]

Howdy

Before I would do any of that I would put a fuel pressure gauge on the fuel rail, see what your pressure is when the key is turned ON, and after it sits for 10 seconds. Also check fuel pressure when its running. While you may have a leaky injector or fuel pressure regulator, your throwing money at it with testing.

So far it appears this is what the PO has done

 

[Bt Doctur]

Left a message. once the injector retainers are removed and fuel rail is removed, the injectors simply lift up and out. a bit of wd 40 for the O rings will aid in removal

 

[Tntjewell]

Thanx for the replies. Do you think, this could be the next step in diagnosing the stalling when starting?

 

[alldodge]

Yes, the issues I read are telling me that folks are replacing parts but nothing is said as to why the parts are being replaced from test results. Something like the fuel pump was replaced because it did not reach 60psi when restricted. The IAC was replaced because you could start it giving a little throttle but soon as the throttle was pulled back it died.

Shift cable and water pump replacement has nothing to do with starting.

Need to see some full pump pressure numbers before I would suggest changing anything else in the fuel system

 

[tpenfield]

Seems like the fuel is draining down and the starting cycles are re-priming the fuel lines. I think the injector replacement idea may just be just a shot in the dark.

 

[Tntjewell]

Just checked the fuel pressure, it reads 40 psi.

 

[alldodge]

Just checked the fuel pressure, it reads 40 psi.

A pressure of 40psi is within the norm, manual shows 43 at idle. Was this running at idle or just turned ON?

Have you tried to start by moving the throttle forward (giving it more gas so to speak)?

 

[Tntjewell]

The pressure read was at idle. I have tried starting with the throttle forward it works, but once I retard the throttle to put it in gear it dies.

 

[alldodge]

The pressure read was at idle. I have tried starting with the throttle forward it works, but once I retard the throttle to put it in gear it dies.

This is a classic example of the IAC going out or the wiring to the IAC (P/N 803149). The IAC is located on the throttle body.


I know your info given from the prior owner list this was replaced, but this item is not working.

[
CLEANING AND INSPECTION IMPORTANT: DO NOT use cleaners containing methyl ethyl ketone. It is not necessary
for cleaning throttle bore and valve deposits.
IMPORTANT: DO NOT allow the TP sensor and IAC valve to come into contact with
solvent or cleaner.
IMPORTANT: Use care when removing gasket material from plenum and throttle
body. Failure to do so could result in damage to the plenum and throttle body.
1. Carefully remove all gasket material from plenum and throttle body.
2. Thoroughly clean all parts of throttle body. Make certain that all passages are free of dirt
and burrs.
3. Inspect mating surfaces for damage that could affect gasket sealing.
4. Inspect throttle body for cracks in casting.
5. Inspect throttle plates, linkage, return springs, etc., for damage, wear and foreign
material.
6. Check plenum for loose parts and foreign material.

 

[Tntjewell]

Alldodge, thanx for the detailed response! Was thinking along same lines regarding IAC.