mercruiser 7.4 mpi cold start stalling

[jmowood]

i cant seem to figure this out. she starts and stalls 6 to 8 times when cold then runs awsome. i replaced the TPS and the AIC and still nothing better. the problem only happens when its a cold start from in the morning. boat is in my yard on blocks and outside temp is around 33 degrees.

 

[alldodge]

Howdy jm

Going to need a bit more info to get started, and I'll list some moderators at the end so one of them can move this to the Mercruiser section, your in the outboard section. No biggy, happens all the time

Can you give us the serial number of the motor and the year, also it probably has a bravo outdrive, but just to verify?
Have you done any kind of maintenance prior, like plugs, cap, rotor, fuel filter or the like?

Ga boater Fun Times Bondo could ya'll move this one please

 

[GA_Boater]

Got it AD.

Welcome to iboats, JM

In addition to what AllDodge has asked, has she been on blocks for a while? Is this a new issue?

 

[jmowood]

How do I switch it to mercruiser from outboard. I have done a complete tune up plugs wires cap rotor fuel.filter serial number 0L310661. With bravo 3 1999

 

[jmowood]

Sorry. Didn't see other questions. Not on blocks long. About 6 months and it's new issue from last year. I tuned it up is there a vac line towards the distubitor I may have knocked off

 

[alldodge]

Don't worry about moving the thread, it has already been moved to the Mercruiser section.

Your serial number shows it has a MEFI 3 computer and uses the first gen cool fuel, like mine. Your vacuum line should not be an issue unless it is disconnected or broke. There is no vacuum line going to the distributer. The vacuum line is used to increase the fuel pressure as the throttle body is opens during acceleration.

Don't think it's the IAC, if it was the motor wouldn't idle even when warm.

How long have you had the boat and how long has this issue been going on?

 

[jmowood]

Got the boat in Aug 2015 ran it for a month and zero issues. I winterized it on blocks in my yard in Sept did a fresh tune up last week and changes the Tps and iac. Thinking it would fix my issue. Runs like a charm other than cold starts. It has been below 30 at night so I am wondering if it's just the cold weather. At night I keep a heater on the outdrive with a tent blanket to keep the heat on the outdrive.

 

[alldodge]

Guessing maybe a few more words would be needed to clarify, what I'm hearing is: got it in Aug 2015 and had no issues.
In Sept 2015 did a tune up and replaced the IAC and TPS.

Don't know why the IAC and TPS was changed if there where no issues.

Now you have an issue with cold starts.

You said it's been below 30 degrees, and at night your keeping a heater on the outdrive.

If the drive is in the down position there is no water in it, no need to keep a heater on it. Now if your not draining the engine block or keeping heat on it, you could be looking at a cracked block

What am I missing?

 

[jmowood]

Replaced the sensors because after the tune up and spring start up I had the issues. The heater is to prevent ice in the outdrive and yes drive is all the way down. I'm anal about freezing so I did the heater thing.

 

[alldodge]

Replaced the sensors because after the tune up and spring start up I had the issues. The heater is to prevent ice in the outdrive and yes drive is all the way down. I'm anal about freezing so I did the heater thing.

OK there could be a timing issue going on, or the vacuum line going to the plenum may be damaged. Did you just remove the throttle body to change out the IAC or was the plenum removed?

Trying to find out what may have been disconnected or damaged during repair.

Understand the being careful not to have anything freeze, but your good with the bravo drive, with it down all water comes out. Only the Alpha drive you need to worry about, but still not that much if all the way down

 

[jmowood]

Just removed the tb to do the sensors.

 

[alldodge]

Gaskets all good or replaced, correct?

Would be real nice to know if there are any codes showing up, have you checked?

Should have 43 psi on the fuel rail.

There are two other sensors (MAP and temp) but would like to know what is happening before replacing any of them. If the temp is showing that the motor is at operating temp when it's cold, the fuel would be leaned out and should cause a stall. Now the temp sensor could be fine but may have a bad connection. This same thing can happen if the fuel pressure is not right.

 

[jmowood]

I can get a purl pressure tester and check. I don't know how to get the codes

 

[jmowood]

The map sensor seems a little loose. It swivel back an forth a little. Temp on the dash seems to be working fine.

 

[alldodge]

Don't bother with the MAP, don't see how it will effect what your seeing. I'm thinking the Engine Coolant Temp (ECT) sensor or the connection to it is the problem. Below is how to test the circuit and you will need a test light and Volt Ohm meter. You don't need to remove the sensor to test. Note: circuit 41o comes from the ECM and is checked at the ECT plug

CAUTION : If the senor is bad and needs replaced, it is hand tightened, then turned an additional 2 1/2 turns, no more then that





Don't know what a purl tester is, but fuel pressure is tested at the shrader valve on the fuel rail with a gas high pressure gauge which can read up to a minimum of 60 psi. Something like this
http://www.walmart.com/ip/41280735?...39345729&wl4=&wl5=pla&wl6=98365151529&veh=sem

 

[jmowood]

Is the ECT on the tstat housing on on the port side of the plenum

 

[alldodge]

Is the ECT on the tstat housing on on the port side of the plenum

It is in the thermostat housing and could be on the port side. There is a gauge sender which has one wire on it, the other has a plug with two wires.

 

[jmowood]

Is there a step by step procedure on line how to chech the ECT circuit

 

[alldodge]

Is there a step by step procedure on line how to chech the ECT circuit

See post 15

 

[jmowood]

step 2 gave me 3.60 volts,
step 3 gave me 3.70 volts