2000 5.7 GSi PEFS MAP sensor?

[ChrisCraftFan]

I have a possible vacuum leak or a bad MAP sensor. Map sensor shows over 2.5 volts at idle and the idle wanders. When I look at it it looks like it was replaced but looks like an automotive version. Does anyone know if there is a difference? Volvo Penta wants about $200 for their Mao sensor.

 

[alldodge]

A MAP is a MAP so long as it uses the same scale (1 bar in most cases)

What is your serial number?

 

[ChrisCraftFan]

serial number
4012018939

 

[ChrisCraftFan]

Also if anyone knows how i can test the MAP. is there a scale of voltage that coincides with vacuum? like at 14 inches of vacuum its 1.56 volts or something

 

[alldodge]

List VP 3850396

1 Bar map
This is what I'm finding
REPLACEMENT FOR MERCURY MARINE
# 805217A1, 864856A1, OMC/VOLVO 3850396 Sierra 18-7684, SMP AS5

 

[alldodge]

Finding
4.6V with ignition ON
Around 1.46V at idle (depends on vacuum)

 

[ChrisCraftFan]

Thanks!!! I am seeing 2.33V at 600 RPM something seems wrong. Could be my black smoke issue.

 

[alldodge]

Check your vacuum reading. Can connect it to the line which feeds the regulator
Check your fuel pressure, should be 30 psi for TBI

 

[Tail_Gunner]

For future reference you will find 1990/1993 454 ss trucks and marine tbi fuel injection parts work quite well together.

Those trucks were GMs attempt towards hi performance fuel injection. You might also notice those yrs and those trucks were exclusively used a 30lb fuel pressure rail...Rumor has it of course.

 

[Tail_Gunner]

MAP Sensor Test (P0106, P0107, P0108) (GM 4.3L, 5.0L, 5.7L)

How to test the GM MAP Sensor (4.3L, 5.0L, 5.7L). Symptoms of a BAD MAP Sensor. Troubleshoot and test codes: P0108 (OBD II) or codes: (pre-95 OBD I). Testing The MAP Sensor. Multimeter MAP Sensor Test.

troubleshootmyvehicle.com

That link should provide you with the values and how to guide.

, to get this show on the road, this is what you need to do:

1. 1
   If necessary, remove the MAP sensor from the engine to disconnect it from the vacuum hose or line that supplies it intake manifold vacuum
   
   If you needed to disconnect the MAP sensor's electrical connector to remove it or its vacuum hose, then reconnect it now since this test requires that the MAP sensor be connected to its 3-wire electrical connector.
2. 2
   With a piece of vacuum hose, connect the MAP sensor to the vacuum pump. The vacuum hose that you need to use has to fit tightly around both the vacuum pump and MAP sensor's inlet vacuum nipple.
3. 3
   OK, grab your trusty multimeter, select Volts DC mode on it and with the red multimeter test lead, pierce the wire labeled with the number 2 in the image viewer.
   
   NOTE: The MAP sensor harness connector needs to be connected to the MAP sensor, so you'll need to either back-probe the connector or use a wire piercing probe to get to the signal inside the wire (to see what a wire piercing probe looks like: Wire Piercing Probe Tool).
4. 4
   Connect the black multimeter test lead directly to the battery negative (-) terminal.
5. 5
   Turn the key on but don't start the engine. This will enable the manifold absolute pressure (MAP) sensor to get power in the form of 5 Volts and Ground from the PCM (Powertrain Control Module= Fuel Injection Computer).
6. 6
   With the Key On and the Engine Off and without any vacuum applied to the MAP sensor, your multimeter should register 4.7 Volts DC.
   
   Now, as you pump up the vacuum pump, the MAP sensor should make your multimeter register the following voltages at the following vacuum values (they may differ a little on your specific GM car or pick up or SUV or van or mini-van):
   
   1.) 0 in. Hg ...... 4.7 Volts.
   
   2.) 5 in. Hg ...... 3.9 Volts.
   
   3.) 10 in. Hg .... 3.0 Volts.
   
   4.) 20 in. Hg .... 1.1 Volts.
   
   Repeat this test step several times and each time, you should see the same values on your multimeter.
7. 7
   If you're using your mouth to suck on the MAP sensor's vacuum hose, then what you should see is the voltage going down. You won't be able to get it to 1 Volt DC on lung power. The important thing is just to see the voltage go down. When you stop and release whatever vacuum you created with the good ole’ lungs, the MAP voltage should go up to about 4.7 Volts.

OK, let's take a look at what your vacuum pump test results mean:

 

[ChrisCraftFan]

That's awesome! A few days ago i pulled the trigger and sent my TBI to the guy at SPR Performance. He is a super helpful guy and he is going to go thru it completely including bushing the shaft, verifying the injectors, checking the TPS and IAC sensors. I can test the MAP while I wait for it to come back. Thanks for all the help!!!

 

[ChrisCraftFan]

I have a possible vacuum leak or a bad MAP sensor. Map sensor shows over 2.5 volts at idle and the idle wanders. When I look at it it looks like it was replaced but looks like an automotive version. Does anyone know if there is a difference? Volvo Penta wants about $200 for their Mao sensor.

Okay checked quit a few things and found nothing so far. Still show vacuum at 16 when idle and 21 when 1600 rpm. Dumping too much fuel. Thinking I should check valve lash. Wondering if I can get the valve covers off with exhaust still on? Its a new motor and came with valves adjusted. I am wondering if a couple have the rockers to tight? I have already replaced riser gaskets twice and don’t want to again if I can avoid it. It’s tight but has anyone been abl to remove covers with exhaust on?

 

[alldodge]

Still show vacuum at 16 when idle and 21 when 1600 rpm.

You have a vacuum leak and would also explain why it runs rich.
Its a new motor, who installed the intake?

 

[ChrisCraftFan]

I did. Cannot find a vacuum leak. I tried spraying carb cleaner found nothing. Did a smoke test found nothing. Starting to believe that I have a rocker or two thats to tight making valve hang open. i was told that the valves were adjusted so did not check them. going thru hell. I thought a Volvo Penta shop could find it faster. They had it 2 months and gave up.

 

[alldodge]

Compression and leak down test will advise if the valves are not seating
If the intake is leaking on the underside spraying it will not cause it to show up.

Did you ever check the fuel pressure?

 

[Tail_Gunner]

You have a new engine,
How did you set the timing
Have you changed the factory injectors?
Have you checked the fuel pressure regulator?
Have you checked the fuel pressure itself?
Have you checked The IAC/TPS sensors?.......................IAC does control vacum idle...
Your vacum increases at 1500?
Does it surge once warm?

 

[ChrisCraftFan]

new engine from flagship marine engines.
The marina did a compression test said it was very good. Did not give me numbers
fuel pressure is 30 idle and load consistently.

i did base timing with paper clip. Marina also checked it.
TBI was sent to SPR Performance. Cleaned and verified injectors. Replaced tps and iac. They were a little intermittent. Replaced diaphragm on pressure regulator.
yes at 1600 rpm vacuum is 21 and steady. Timing also advanced to 19.
no surge just goes flat when hitting throttle puffs black smoke and then catches up.
I have never done a leak down test. Anyone know if the inexpensive ones from Amazon are any good?

my two thoughts are misajusted rocker (too tight). And intake leak on the inside. I was pretty careful installing intake but I guess it could leak on the inside?

 

[alldodge]

I don't see your issue being from a valve being to tight. If they were to tight you would get backfiring

Also not so sure about the marina testing. Compression test is good and fuel pressure is 30 psi. How did they test it and how was it placed under load?

With vacuum going higher as throttle increases the fuel pressure should start to increase then go lower, then back up. The increase/decrease would be a couple psi.

What does the motor idle at when placed in base timing mode?

 

[ChrisCraftFan]

The valve thoughts came from a couple good friends and old racing buddies that worked at GM and worked on these TBI engines on the GM trucks. A valve hanging open slightly could cause it to have lower vacuum evidently. No personal experience here. We just thought we should eliminate it as an issue.

I have tested fuel pressure myself several times and have a new fuel pump. marina also tested it. Under load means we had it in the water and opened it up. did not notice any change in PSI. Seemed to remain steady to me. I have not personally done a compression test. Since it is a new motor and the marina did the compression test, it seemed i didn't need to.

I will check the rpm in base mode tonight but its around 1000 rpm I believe. it increases when I put the jumper in.

Thanks you everyone for help!!! this one has me stumped.

 

[ripjmk]

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?