No Start / Merc 1998 EFI 5.7

[300sflyer]

Late in the day on Sunday, I had an issue with my port engine. It is a 98 5.7 Merc, throttle body EFI, serial # 0L067833. It would crank over ok, but it would not fire up. Previous to that, it was difficult to start sometimes, so all I did was open the throttle slightly, and it would start right up. Occasionally, it would stall, but fire right back up again. I checked just about everything I could think of, and found nothing obviously wrong.

Out of desperation, I swapped the ECM from the starboard engine, and it then fired up. There were no loose connections, or any corrosion on the terminals. Thinking it was then a faulty ECM, to confirm that, I then put the "bad" one in starboard engine, and it too started and ran just fine.

Now I'm wondering what the original problem was?...Any ideas?

Thanks for your help!

 

[scoflaw]

Re: No Start / Merc 1998 EFI 5.7

IAC valve, my guess. Common merc problem, but a quick fix

 

[300sflyer]

Re: No Start / Merc 1998 EFI 5.7

Would a scan confirm that, or would the data on the ECM be erased when the 2 connectors were removed?

 

[scoflaw]

Re: No Start / Merc 1998 EFI 5.7

Had a similar issue with my efi 98 and that fixed it for me. I'm not even sure if a 98 is scanable.

 

[Don S]

Re: No Start / Merc 1998 EFI 5.7

Try opening the throttle a little bit and see if it starts. I assume you are getting spark, are the injectors squirting fuel while you are cranking?
What's the serial number of your engine?

 

[300sflyer]

Re: No Start / Merc 1998 EFI 5.7

Try opening the throttle a little bit and see if it starts. I assume you are getting spark, are the injectors squirting fuel while you are cranking?
What's the serial number of your engine?

Unlike the starboard engine, it has always been difficult to start since I have owned it. Open the throttle a touch, and it starts right up except for the one time on Sunday, where it woulud not start no matter what I did. That is when I swapped the 2 ECMs. The serial # is in my first post.

 

[Don S]

Re: No Start / Merc 1998 EFI 5.7

I must be brain dead this morning, I didn't remember anything from your original post by the time I got to the bottom of the thread. :facepalm:

 

[Don S]

Re: No Start / Merc 1998 EFI 5.7

When you swapped the ECM did you try the one that wouldn't start on the good engine? If it then won't start, I would have to say the problem is in your ECM.

 

[300sflyer]

Re: No Start / Merc 1998 EFI 5.7

When you swapped the ECM did you try the one that wouldn't start on the good engine? If it then won't start, I would have to say the problem is in your ECM.

Better read my first post one more time.

 

[Don S]

Re: No Start / Merc 1998 EFI 5.7

No thanks

 

[300sflyer]

Re: No Start / Merc 1998 EFI 5.7

As stated in my first post, both engines now run after the swapping the ECMs. The port one is still difficult to start, unless I open the throttle slighty.

What I'm now wondering is, will a scan now find the original problem with the port engine?

 

[scoflaw]

Re: No Start / Merc 1998 EFI 5.7

The scanner will hook up to the T5 ignition, not sure how much info will be there for you. If that's the only issue you have with that motor and it runs fine the rest of the time, I would install a new IAC.

 

[TilliamWe]

Re: No Start / Merc 1998 EFI 5.7

flyer, I get what you're saying. I wonder too will the scanner get a readable code from the ECM that you have now unplugged and installed on the other engine. My guess is that a code, if any is stored in there.

Regarding IAC. It stands for Idle Air Control. While I don't have a ton of experience with them, I have been around when a couple have gone bad. And neither caused the engine not to start. By its natural function, when an IAC fails, it doesn't allow the motor to stay running at idle. I know one guy here is saying it fixed his "no start" issue, but I'd be leery of just throwing parts at it. Try the scan tool, but don't be too surprised if it doesn't tell you much/anything.

 

[300sflyer]

Re: No Start / Merc 1998 EFI 5.7

Thanks for the info. I guess a scan is the next step, to see what might be there. Will report back once that is done.

 

[Fun Times]

Re: No Start / Merc 1998 EFI 5.7

Do you own a scan tool? On you're MEFI 1 or 2 ECM/EFI system, you should not see or set a code for the IAC valve, The newer version of engines do set a fault.

When you hook up a scan tool you should see the count range within,
Idle Air Control IAC Counts (Steps) 0-40 Counts
Minimum IAC Position Counts (Steps) 0-40 Counts
Idle Air Control Follower Counts (Steps) 0 Counts

You may need to just clean the IAC area as it gets dirty in there in short time.

IDLE AIR CONTROL (IAC) VALVE
The purpose of the IAC valve assembly is to control engine idle speed, while preventing
stalls due to changes in engine load. The IAC valve, mounted in the throttle body, controls
bypass air around the throttle valves.

By moving a conical valve known as a pintle, IN, toward the seat (to decrease air flow), or
OUT, away from the seat (to increase air flow), a controlled amount of air moves around the
throttle valve. If rpm is too low, more air is bypassed around the throttle valve to increase
it. If rpm is too high, less air is bypassed around the throttle valve to decrease it.
The ECM moves the IAC valve in small steps, called counts. These can be measured by
scan tool test equipment, which plugs into the DLC.
During idle, the proper position of the IAC valve is based on engine rpm. If the rpm drops
below specification and the throttle valve is closed, the ECM senses a near stall condition
and calculates a new valve position to prevent stalling.
? Engine idle speed is a function of total air flow into the engine based on IAC valve
pintle position + throttle valve stop screws and PCV.
? ?Controlled? idle speed is programmed into the ECM, which determines the correct
IAC valve pintle position to maintain the desired idle speed for all engine operating
conditions and loads.
? The minimum idle air rate is set at the factory with stop screws. This setting allows
enough air flow by the throttle valves to cause the IAC valve pintle to be positioned a
calibrated number of steps (counts) from the seat during ?controlled? idle operation.
? If the IAC valve is disconnected and reconnected with the engine running, the idle
speed may be wrong. In this case, the IAC valve can be reset by doing the following:
turn off engine, wait ten seconds, and restart engine.

You will notice there is no IAC code in the list below.
Diagnostic Testing . . . . . . . . . . . . . . . . . . . 5G-53
Code 14 Engine Coolant Temperature
(ECT) Sensor Circuit . . . . . . . . . . . . . 5G-53
Code 15 Engine Coolant Temperature
(ECT) Sensor Circuit . . . . . . . . . . . . . 5G-56
Code 21 Throttle Position
(TP) Sensor Circuit . . . . . . . . . . . . . . . 5G-58
Code 22 Throttle Position
(TP) Sensor Circuit . . . . . . . . . . . . . . . 5G-61
Code 23 Intake Air Temperature
(IAT) Sensor Circuit . . . . . . . . . . . . . . 5G-64
Code 25 Intake Air Temperature
(IAT) Sensor Circuit . . . . . . . . . . . . . . 5G-66
Code 33 Manifold Absolute Pressure
(MAP) Sensor Circuit . . . . . . . . . . . . . 5G-68
Code 34 Manifold Absolute Pressure
(MAP) Sensor Circuit . . . . . . . . . . . . . 5G-71
Code 41 Ignition Control (IC) Circuit . 5G-74
Code 42 Ignition Control (IC) Circuit . 5G-76
Code 43 Knock Sensor (KS) Circuit . 5G-78
Code 44 Knock Sensor (KS) Circuit . 5G-81
Code 45 Ignition Coil Driver Fault . . . 5G-84
Code 51 Calibration Memory Failure 5G-86
Code 52 EEPROM Failure . . . . . . . . . 5G-87
Code 61 Fuel Pressure (FP) Circuit . 5G-88
Code 62 Fuel Pressure (FP)
Sensor Circuit . . . . . . . . . . . . . . . . . . .

 

[scoflaw]

Re: No Start / Merc 1998 EFI 5.7

Long story short, the scan won't come up with anything that's going to shed light on this problem, unfortunately.
Soo like I said earlier, if this is the only issue this engine has, replacing the IAC will be step 1 in attempting to fix this problem you have.
If you don't want to throw the hundred bucks at it, you could swap them out.
There's not to many things on an EFI system that will make your engine do that, if that's the only symptom

 

[300sflyer]

Re: No Start / Merc 1998 EFI 5.7

Thanks for all the info. I don't own a scanner, so my marina will be doing the scan. It will be interesting to see what they come up with.

 

[300sflyer]

Re: No Start / Merc 1998 EFI 5.7

Spoke to my marina today, and they may or may not get to my boat this week, despite me asking them on Sunday to have a look at it. We have a week long trip planned next week, and I need it fixed.

Will an IAC from an auto parts store, be ok to use in my marine engine? A Merc one is stupid money up here in Canada, and I can't seem to find a Sierra one up here. I can pick one up at my local parts store for about $70.

 

[scoflaw]

Re: No Start / Merc 1998 EFI 5.7

Stupid money is what boating is all about. Gotta pay to play.

Google your part # on Ebay and look at your options

 

[NHGuy]

Re: No Start / Merc 1998 EFI 5.7

Swap the IACs to check. If the problem follows the IAC you will know that's the culprit.
Fun Times also said "You may need to just clean the IAC area as it gets dirty in there in short time."
If you swap it and the problem does not move it's a different issue, maybe a connector or a ground. Grounds can be a pain but at least you aren't throwing parts at a situation-guessing.