2000 5.7 GSi PEFS MAP sensor?

[Tail_Gunner]

It could be poor combustion causing the higher than normal inlet manifold pressure at idle. You say fuel pressure, cylinder compression and timing are all good. The MAP seems to be responding to manifold pressure, so something must be enriching the mixture beyond acceptable for good combustion. The engine coolant temperature sensor (ETC) enriches fuel mixture during cold starts and could be the problem if it is reading low (sensor resistance is high). It might be worth checking the sensor, sensor connector and wiring to the ECM, or has this been checked already?

You are quite correct with the ETC sensor, mefi uses a cold enrichment circuit. much like a mechanical choke.

 

[ChrisCraftFan]

Thanks! Yeah the coolant temp sender has been replaced and we can see the temperature rising to normal on the scan.

Talked to the engine builder it seems unlikely they adjusted the valves incorrectly. there's a chance but they are a reputable builder.

That kind of leave me as the guilty party with the intake install. Not sure how it could be leaking on the underside but also not sure what else to look at. it was a new gasket and I installed it on the engine stand in my garage. was as careful as I could be.

We all agree that Vacuum of 16 at idle is too low right??? it puts the map voltage at about 1.8 or so. If we all seem to agree its low I will pull it all apart and redo the intake gasket. Not sure what I could do differently though? Hopefully the intake comes off without removing the valve covers. That's just a bunch more work and new riser gaskets.

 

[Tail_Gunner]

Thanks! Yeah the coolant temp sender has been replaced and we can see the temperature rising to normal on the scan.

Talked to the engine builder it seems unlikely they adjusted the valves incorrectly. there's a chance but they are a reputable builder.

That kind of leave me as the guilty party with the intake install. Not sure how it could be leaking on the underside but also not sure what else to look at. it was a new gasket and I installed it on the engine stand in my garage. was as careful as I could be.

We all agree that Vacuum of 16 at idle is too low right??? it puts the map voltage at about 1.8 or so. If we all seem to agree its low I will pull it all apart and redo the intake gasket. Not sure what I could do differently though? Hopefully the intake comes off without removing the valve covers. That's just a bunch more work and new riser gaskets.

Factory intake and factory cam?, a new engine with 16 inches at idle is not up to par.I believe you have two problems being rolled up into one.

Timing
Vacum leak

One thing you have not done is to take a neon light and shine it on the injector spray pattern while it is running. The Neon strobes the pulses and one can see any irregularity...Drips or even going static...static just a continual burst of spray no pulses..

 

[ChrisCraftFan]

Thanks!
Yes Factory intake and cam.
I think somehow i got a vacuum leak on the underside if the intake. No idea how or what is going on with that but, I cant find a leak anyplace else. (Carb cleaner spray and smoke tested) Just hate doing all that work not really knowing.

As for timing Its been checked by me at least three times and by the marina twice. not sure what else to do there? It also advances just like the book said it should. (19 at 1600 RPM) I was going to check what RPM it goes to when i add the paperclip but i got busy and now its getting dark.

Not sure where to get a neon light? but, the injectors where inspected by SPR Performance along with the TBI Rebuild. I have watched them and looks like a nice pulse and cone. I did not use a neon light though. Or are we thinking the mefi is sending bad info to them? The mefi was sent to Bob at OBD Diagnostics and he found nothing wrong with it. I wish i could locate a mefi to try just to eliminate that but no luck there.

Thanks everyone I love getting some new ideas!! I am running out of them. I just cannot let this thing beat me!!!! LOL

 

[ripjmk]

I don't see it being a vacuum leak as all that would do is give you a higher than normal idle speed (the MAP would keep the mixture correct). Unless the leak was only local to the MAP and the manifold vacuum was normal! Are you sure there is not a pin hole in the MAP hose?
You say the timing has been checked, but has the valve timing been proved correct? If the valve timing is off I could see that causing your issue.

 

[ChrisCraftFan]

The vacuum seems low to me. I understood that the MAP would see higher voltage and add more fuel. I replaced the hoses and smoke tested. Vacuum reading was taken from pcv hose. Maybe I am wrong about MAP voltage? I also thought the IAC controlled idle speed. Maybe I am wrong about that? not sure how to prove valve timing?

 

[alldodge]

The IAC controls idle
ECM controls fuel injection pulse width based on rpm and MAP

 

[Tail_Gunner]

Actually if you take the fuel injection out of the loop and think along the lines of a carb...your hesitation would be an overly rich jet. There are numbers on these injectors, can you post them?
The IAC does affect the vacum also.

 

[ripjmk]

one other thought, have you disconnected the fuel cell vapor line to check that the float valve is sealing completely? If it is allowing even a small flow of fuel to pass to the inlet manifold it would mess up mixture at idle.

 

[alldodge]

one other thought, have you disconnected the fuel cell vapor line to check that the float valve is sealing completely? If it is allowing even a small flow of fuel to pass to the inlet manifold it would mess up mixture at idle.

Post 3 = SN
Cross check SN will find there is no float valve

 

[ChrisCraftFan]

No visible numbers on the injectors SPR Performance checked them out for me. The tops were kind of rusty. They appear to be OEM just can’t get the numbers.
it’s rich alright!!! black smoke when accelerating. New iac installed by SPR Performance. Feel that the map is telling it more fuel at idle and its too much fuel on acceleration and by the time I get to 1600 rpm map drops to below 1 volt and boat takes off and starts running good.

 

[ChrisCraftFan]

I did Check the fuel pump vent no fuel in that line. I even ran with a clear hose on it and watched it. No fuel there. Of course it’s also a new fuel pump, filter, fuel lines.

 

[Tail_Gunner]

No visible numbers on the injectors SPR Performance checked them out for me. The tops were kind of rusty. They appear to be OEM just can’t get the numbers.
it’s rich alright!!! black smoke when accelerating. New iac installed by SPR Performance. Feel that the map is telling it more fuel at idle and its too much fuel on acceleration and by the time I get to 1600 rpm map drops to below 1 volt and boat takes off and starts running good.

Future reference....TBI injector 852956A1
Quite expensive...
Standard motors cross-reference and they cross-reference to that part number.
TJ17

Fuel Injector - New

POP: C Per Car: 1

• COMP/OE #:852956A1
• COMP/OE:Mercruiser

Fuel Injectors

I have a 1999 Twin volvo penta 5.7 engines. I wanted to know is there a difference between the TJ11T and TJ11 Injectors? If so what is the difference and which is the correct one for me to use? Thank You

forums.iboats.com

 

[ripjmk]

Well there's not much left that could be wrong! If it runs fine at 1600 and above with expected vacuum but rich at idle with low vacuum the issue must be a variable not a constant. So something is changing the mixture at speeds below 1600. The only thing not mentioned so far that can change both mixture and timing is the knock sensor. Not to say the sensor is bad as it only happens at low rpm. So what could make it knock at low rpm? High compression (get compression test results), retarded timing (checked OK), poor fuel quality (is it being fed fresh fuel?), spark plug gap ( ensure .045 gap not .060 plugs fitted).

 

[ChrisCraftFan]

In the many things I have tried I tried tj17’s. The engine just surged badly. I was lucky they took them back!

 

[Tail_Gunner]

In the many things I have tried I tried tj17’s. The engine just surged badly. I was lucky they took them back!

Now that is odd, i used them with great success in a 01 4.3 penta, Why the surging... rich? or lean? They are 5.7 cop car injectors..1994

 

[ChrisCraftFan]

I will have to do my own compression test if I want the numbers. Knock sensor is new Volvo PENTA. I can see it on my mefi scan software and it’s not activating. Good idea on plugs. I think I read someplace that the wrong gap might cause low vacuum. Hmmmmm. They are not fun to get to but worth checking. I can make sure what plug the marina put in. They replaced them

 

[ChrisCraftFan]

I m not sure rich or lean. Did not spend a lot of time with them. Started and ran a little. Surge was pretty bad so I pulled them.

 

[alldodge]

Its not the knock sensor. If it was there would be a code ,and what does a knock sensor do, it tells the ECM to retard the timing. The timing has not even advanced yet so nothing to retard

Its getting to much fuel for the amount of air its getting. As rpms increase it gets to the point where the air to fuel ratio is correct and it runs better.

I'm leaning toward its a throttle body issue or the intake gasket (TB or intake). The TB consisting of the injectors, IAC and TPS. Hope the TB was not opened up by SRP.

With motor OFF and key ON use the scanner and watch the TPS voltage change as throttle moves from idle to about 1/2 way.

Remove the IAC and see if the tip is closing off the idle port. Do this by measuring the length of it and compare to depth of hole. Turn key ON with IAC out and does it retract?

Cycle the key ON and OFF a few times to see if the injectors leak

 

[ChrisCraftFan]

well SPR rebuilt my TBI. I looked around and he seemed to have the best reputation. Is there something I should know??? He also installed new iac and tps. Adjusted initial voltage on the tps.
I will definitely run those tests next chance I get. Thanks!