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

[RaceCarRich]

My 2005 5.0L MPI had a fuel rail test valve. Worked fine with my Harbor Freight Fuel Pressure test kit ($20 after 20% coupon).

 

[DIY1111]

I read the fine print on that kit - says specifically not for GM ? You say it worked with your rail system ?

 

[RaceCarRich]

Yes. Says doesn’t fit GM throttle body systems. We have port injection.

 

[alldodge]

The GM TBI uses this adapter because the first years didn't have a schrader valve

 

[DIY1111]

Tested Fuel Pressure at idle and at a higher RPM ( not sure what RPM, should have looked at tach ) - stayed at steady 35 psi the whole time.

Boat runs and re-starts really well once warm for 5 minutes or so.

Initial starting seems to have gotten worse lately ( not sure if it has anything to do with ambient temp which has gotten colder ). It can take 5-8 attempts. Once it starts it will run really rough - you can here the engine surging, struggling to find idle, and the fuel pump motor, the pump with the cooler, surging slowly and faster in unison with the engine searching for idle.

Then, after a minute or so, she evens out and runs great. After a few more minutes, she'll start up immediately.

?????

 

[alldodge]

Pressure should be 43

Assuming a Bravo drive it should have 2 fuel pumps, a boost pump by the canister filter with inline filter, and the cool fuel on port side.

Need to find out if its a restriction, weak pump or regulator

 

[DIY1111]

In shop manual it mentions 35 psi as a minimum baseline. Which is the correct # ? 35 or 43 ?

Working on that cool fuel pump is horrible on my boat - very! tight to work on... in terms of restrictions, where aside from the water fuel separator and the ss filter near the primary fuel pump should I check ?

And, could this low pressure be related to the cold start issue ?

 

[alldodge]

43 is correct, the 35 is minimum needed

Lower pressure will cause the motor to not have enough fuel. The injector pulse opens/closes it for a length of time. If pressure is lower then there is less fuel being released each time it opens. When the motor is cold it needs more fuel just like a carb motor with a choke.

If the pump is having a hard time drawing fuel then there will not be enough to pump. My guess right now is its either the cool fuel pump or regulator

Start at the tank and the barbed fitting. The fitting is an antisiphon valve which can get clogged.


The fuel lines can collapse inside. The filter or filters can get clogged

 

[DIY1111]

Makes sense. I'll try to get to boat today and double check the fuel pressure at a higher idle.

First thing - I'll by-pass the fuel tank and run her off a (6) gallon tank to see if pressure raises.

After that, I can replace the SS pre-filter near the primary fuel pump. The water fuel separator is clean.

• Can I test the cool fuel pump without removing it ?
• How about the regulator ? Is that something I can check ?. ( I can't stress enough how the cool fuel mech is in a b*tchy spot - way low with my motor bed in the way ! )

Is it possible that the cool fuel pump is not getting enough voltage ?

And, what part does the primary fuel pump play in all this ? Is that a potential culprit ?

 

[alldodge]

Can I test the cool fuel pump without removing it ?

Can power it directly at the fuel pump relay. Remove the relay and jump power to the contact

How about the regulator ? Is that something I can check ?. ( I can't stress enough how the cool fuel mech is in a b*tchy spot - way low with my motor bed in the way ! )

Yes we all know its a pain to get at it. Only way to check the regulator is to remove it and use air pressure with regulator and slowly increase pressure until it opens

Is it possible that the cool fuel pump is not getting enough voltage ?

Anything is possible but not very probable. Can check power at the fuel pump relay

And, what part does the primary fuel pump play in all this ? Is that a potential culprit ?

The other fuel filter and pump was Merc's trying to fix vapor lock issues and it didn't work. My BB only has the cool fuel pump and has no issues

 

[DIY1111]

Should I check the fuel pressure reg on the fuel rail ?

 

[alldodge]

Don't think its needed. Its called a reg but actually does not regulate, it only reduces some pulsing

 

[DIY1111]

I just rechecked the fuel pressure at idle and at 2000rpm's - it's still 35-36 psi. When I turn the engine off, the psi goes to 30psi and stays there. Oddly enough, the engine started right up - but still hunted for idle for a few minutes until she settled down.

As for inspecting the cool fuel pump, can its output be tested, excluding the regulator, to confirm its pumping properly or not ?

I believe I can pull the cool fuel pump pressure regulator - aside from checking it's screen, is there another way to confirm its working or not ? I did pull the vac hose off while engine running and it has good vacuum from engine.

Please note- my distributor was inadvertently turned last year ( not removed ) - I positioned it by eye - so the engine is not timed properly ( I'm assuming this is not related to the fuel pressure being low )...

Thank you for your help !!!!

 

[alldodge]

As for inspecting the cool fuel pump, can its output be tested, excluding the regulator, to confirm its pumping properly or not ?

Yes, cab be removed and a gauge connected directly to the pump output with a valve. Keep fuel line connected to input side and turn pump ON. Bleed air out and pump should produce at least 60 psi and may go to 100 psi

I believe I can pull the cool fuel pump pressure regulator - aside from checking it's screen, is there another way to confirm its working or not ?

Yes previous post

Yes we all know its a pain to get at it. Only way to check the regulator is to remove it and use air pressure with regulator and slowly increase pressure until it opens

The distributor may be off, but he has nothing to do with fuel pressure

 

[DIY1111]

" I'll be back.. "

 

[DIY1111]

Update - still having tough-to-start issue. Based on the fact that when I push throttle up just a small amount when trying to start, And she starts right up, I thought it might be the throttle position sensor (TPS) - but that wasn’t it ?! I hate just replacing parts but it was inexpensive so I went for it - gambled and lost !

Pulled and winterized the boat yesterday.

I’ve read a lot about this issue - seems to be common and the remedies are all over the place, from distributor cap, bad harness wires, ignition module, fuel pressure, rectifier, and so on.

What a PITA !

 

[QBhoy]

Forget all the timing stuff..unless you’ve had it in bits. Get a new Diz cap on it. Replace it every year. All good. 9/10 of the time...this is the cause of issues like this.