2003 5.7 350/300HP MPI - Sporadically Tough to Start

[DIY1111]

It's been a few seasons where the engine will either start on first turn of key, or it will take 3-5 attempts. She has 1030 hours with 95% of them at 3100 rpm's. And, taken care of well ! Recently chased down a gremlin that had me replace many of the sensors ( turned out be a loose dizzy ! ); Idle air valve, new coil assembly and associated parts, new spark plugs, cap, rotor, ignition wires, TPS sensor.

When she won't start right up, I hear the engine searching ( idling erratically ) and the fuel pump fluctuating for about 10 seconds - then all levels off to a smooth idle. There is no rhyme or reason to when this happens. It can be the next day after use or a week of no use. The batteries 'seem' to be fully charged and functioning properly ( I know this is an area of focus - and I hate to assume they are OK - they're 6-7 years old ).

I have read bit about this situation but each time I follow the thread, it never provides what the issue was.

I'd love to get some advice as to where I should focus. Thx

 

[alldodge]

How's the fuel pressure?

 

[DIY1111]

I haven’t checked it. Is there a location to hook up to measure ? I’ll ck it. I have a gauge I made for testing an old car - just a hose with a gauge at the end.

Will this work or do I need an in-line gauge ?

And, what will testing fuel pressure confirm ?

thx

 

[Stinnett21]

You listed IAC but did you replace the IAC Muffler? I have a 2002 5.0 MPI and this was my problem when it experienced very similar symptoms you describe above.

 

[alldodge]

Need a pressure gauge that can read up to 100 psi
Many get a loaner from an auto parts store

There should be a shrader valve on the fuel rail but without a serial number I don't know where yours is

 

[DIY1111]

i replaced the foam muffler a year or so ago. Amazing how that little piece of foam quiets things!

Serial #: OM634400

 

[alldodge]

Schrader valve is item 18 and should be 43 psi at 1800 rpm

https://www.mercruiserparts.com/bam/subassembly/31748/8093/90

 

[DIY1111]

OK - let me make the tester - stay tuned. One other thing that I think is important to mention - when my dizzy was loose - and I re-tightened, I DID NOT time it. I locked in at a location that allowed her to start... Could this be the issue ?

 

[alldodge]

when my dizzy was loose

Could very well cause issues. The motor is not timed with a light, its positioned as shown below. The distributor cap can also cause issues. The cap can look great but be bad. Most with this kind of cap keep a spare on board because they can go out without warning

 

[DIY1111]

I will check cap for the fuzzies.. Getting the # 1 cylinder at TDC is the PITA. All spark plugs have to come out to turn engine - then I need to figure out if its in an compression stroke or not. Is there an easier way ?

 

[alldodge]

Could build the tool in the last pages of this bulletin or use a stop bolt and hand crank the motor over while watching the valves

Also fuzzies may not be there and cap can look perfect but still be bad

 

[DIY1111]

A few questions about the Bulletin - to proper timing for the #1 cylinder should be at 15 deg BTDC ?

And, when they say use a breaker bar and socket - turning the crankshaft bolt with the spark plugs in can easily snap the bolt and then I'd be screwed ! Getting the harmonic pulley to move around and line up 'just right' with the key, or even a remote start can be brutal.

Am I correct in the above ?

And, if so, sounds like the spark plugs have to come out unless theres a way to precisely turn the motor without doing so ?

Note: I'm going to order a new cap/rotor just for the heck of it.

 

[alldodge]

I agree the using a breaker bar on the bolt is bad news, but mentions if it is overshot. It is to get really close, thinking like 1/8 to 1/4 inch on the harmonic balancer. The bulletin is written for a certified Tech which knows about the bolt as you do. Just keep trying until its on target or just barely short

The firing of the distributor is controlled by the crank sensor (CPS) and ECM. Meaning from when the rotor and cap contacts barely are close enough to fire, until there are barely enough getting ready to leave the other side, the spark can happen. This is allows several degrees of advance for the spark to happen

The 15* is my guess the mid point, but just guessing

 

[DIY1111]

Trying to source parts of the TDC test light. What voltage do you think the LED should be ( there's no spec ). Online has 3v, 5, 12 and 24. The spec uses a 9V battery. Not exactly sure how this test light works so I have to assume voltage matters.

 

[alldodge]

All led's operate off the same voltage which is 3V Max. The 470 ohm resistor takes care of limiting the the voltage and current.

My guess (note just guessing) is could get a 12V resistor led (resistor build in) and not use the 470 ohm resistor

 

[DIY1111]

WOW ! Finding a Female, screw on, Schrader valve with a barb on one side that I can connect to the fuel rail to test fuel pressure has not been fruitful. Any ideas ? I have the pressure gauge and hose all set up.

Wait a minute - will this do it ?

https://www.grainger.com/product/3D...cFbKo6xOTwTogWbXHdjQw5kshMAgrd8RoCE5MQAvD_BwE

 

[alldodge]

Which gauge do you have?

 

[DIY1111]

I have a no name, 0-100 psi gauge ( I believe I bought it at LOWES ) that I have used in a similar testing. I made it with the gauge, some FI hose and whatever ending I need to adapt to.

Will the part I referenced above work ? My local Grainger has it in stock.

Then, do I need to test the fuel pressure at start up, or while running or both ?

Thank you

 

[DIY1111]

I had to replace my (2) batteries - one had a post break off while I was re-tightening connections and the other was dead !

The start up issue is still there though ( thought I found the issue but not that lucky )

 

[alldodge]

Schrader valve is 7.7 mm (.302") x 32 T.P.I
The valve at Granger list 1/4 (.250)

Take a tire or bicycle valve stem with you to local store