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  #11  
Old 09-26-2014, 10:06 AM
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Does it idle poorly, or is it relatively smooth? Assuming the exhaust smells of unburned gas, try this- unplug the MAP sensor tube and listen for any changes in the idle speed. If it changes, that's good. If not, check for vacuum at the end. If it has none, find out why.

If you have a multi-meter that will measure voltage and resistance, insert stick pins or T-pins into the wire side of the silicone seal on the MAP sensor wires, sliding past the seal and making contact with the terminals. Bend them so they can't touch each other. Use test leads with alligator clips and attach them to the pins.

Measure the resistance between the MAP sensor ground and ECT ground- IIRC, they share the same ground point and wire to the block. Measure the resistance to ground from the MAP sensor plug's ground terminal and also from the ECT's ground terminal- if you see more than about .1 Ohms, it's too high. If this checks OK, clip the ground lead of the meter onto a good ground on the engine block.

On the MAP sensor plug, Gray is control, Lt Green is the return voltage wire and Black is ground. The Gray should have ~5VDC at all times and the Lt Green should have a range of just less than 1VDC-4.5VDC. At idle, you should see about 1VDC on the Lt Green wire. If it's higher, or the Gray wire doesn't have ~5VDC on it, there's a problem. If the Lt Green wire shows higher voltage, it's telling the ECM that the engine is not at idle- low vacuum means the throttle is open, which requires more fuel. Low vacuum=high voltage=open throttle and since the MAP senses the vacuum below the throttle plate, this is critical.

With the key ON/engine OFF, measure the reference voltage on the Gray wire, using the pin in the ground position and the Lt Green wire should have high return voltage because there's no vacuum. Connect the vacuum gauge to the MAP sensor and pump it a bit- you should see the voltage decrease as the vacuum increases. You may not see much needle deflection on the gauge. If you never see needle deflection or voltage change, it's possible that the sensor is bad. If you have a GM parts provider, you could ask for the large, 1 Atmosphere GM MAP sensor. They also have a small one- this is used on the LTR and inserts in the manifold, so it won't work. The TBI and LT-1 used the same MAP sensor.
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  #12  
Old 09-26-2014, 11:58 AM
SenselessSteve SenselessSteve is offline
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Thanks Mike. That's a great help. I'll order the MAP now.

I see there's an MEFI 1 ECU on the UKEbay also. http://m.ebay.co.uk/itm/381006821572?nav=SEARCH

I'm not sure if there's anyone here who could reflash so might have to send to the states. You don't suppose it would be possible that this one would be plug and play?
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  #13  
Old 09-26-2014, 12:10 PM
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Originally Posted by SenselessSteve View Post
Thanks Mike. That's a great help. I'll order the MAP now.

I see there's an MEFI 1 ECU on the UKEbay also. http://m.ebay.co.uk/itm/381006821572?nav=SEARCH

I'm not sure if there's anyone here who could reflash so might have to send to the states. You don't suppose it would be possible that this one would be plug and play?
depends what it came out of... might work... would be great to confirm which boat it came out of.
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Old 09-26-2014, 12:25 PM
SenselessSteve SenselessSteve is offline
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Thanks Jim. I'll follow these steps tomorrow when I get back to the garage.

The idle isn't so bad although you can certainly hear the characteristics of too much fuel (in that it's doing it's best to combat the rich mixture).

When you say unplug the MAP sensor tube, do you mean remove the MAP sensor from the top of the intake manifold? (Where the small pipe inserts at the rubber seal?)
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  #15  
Old 09-26-2014, 01:03 PM
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Originally Posted by SenselessSteve View Post
Thanks Mike. That's a great help. I'll order the MAP now.

I see there's an MEFI 1 ECU on the UKEbay also. http://m.ebay.co.uk/itm/381006821572?nav=SEARCH

I'm not sure if there's anyone here who could reflash so might have to send to the states. You don't suppose it would be possible that this one would be plug and play?
The only way to know for sure is to read the Checksum. If someone over there has a Tech1 with the marine card or possibly a Mercruiser/Volvo-Penta diagnostic computer, they should be able to do this. I connected our Tech1 to a Mercruiser and although I couldn't operate any functions, I was able to read some data. I have to think someone in a car/boat club has one, or if you have Malibu/Supra/Moomba dealers, they should be able to check this, too. For that matter, they should be able to read your data to see if/where a problem exists. If the numbers don't match what they should see, it's easier to diagnose problems than using a multi-meter (the sensor return and Battery voltages show on the screen).
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  #16  
Old 09-29-2014, 10:16 AM
SenselessSteve SenselessSteve is offline
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Hi Jim. I didn't get to work at the boat on Saturday as planned but finished up in work early today to get to the garage.

I run the checks you suggested and I've discovered that the return voltage (green wire) at the MAP sensor is reading between 2.6 and 2.9 VDC at idle. The plot thickens.

The voltages from the plug all check good when the ignition is on (but not started).

I'm waiting on the MAP sensor arriving that Mike got me a part number for but perhaps there is more to it than this. In your experience, is it common for the MAP to fail and deliver a high reading or is this scenario synonymous with vacuum leak?

I've encountered scenarios were an ECM will substitute a fixed voltage if the MAP fails but perhaps I can rule this out given the variation between 2.6 and 2.9 reading??

Thanks in advance for any input. It's greatly appreciated.

Stevie
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  #17  
Old 09-29-2014, 10:28 AM
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Originally Posted by SenselessSteve View Post
Hi Jim. I didn't get to work at the boat on Saturday as planned but finished up in work early today to get to the garage.

I run the checks you suggested and I've discovered that the return voltage (green wire) at the MAP sensor is reading between 2.6 and 2.9 VDC at idle. The plot thickens.

The voltages from the plug all check good when the ignition is on (but not started).

I'm waiting on the MAP sensor arriving that Mike got me a part number for but perhaps there is more to it than this. In your experience, is it common for the MAP to fail and deliver a high reading or is this scenario synonymous with vacuum leak?

I've encountered scenarios were an ECM will substitute a fixed voltage if the MAP fails but perhaps I can rule this out given the variation between 2.6 and 2.9 reading??

Thanks in advance for any input. It's greatly appreciated.

Stevie
I don't remember the default for defective MAP, but the TPS defaults to 12. Make sure that's operating correctly, too. I don't know if they would run it this rich if the MAP were to fail, though.

Idle, WRT functions of the ECM is <2 throttle position.

Look at the IAC after the engine is turned off. Start the engine and watch the IAC- if the pintle closes and the idle speed is high, it could be a vacuum leak that can't be countered by the IAC and a leaky diaphragm in the MAP sensor could explain this. I think I mentioned applying vacuum to the MAP sensor- if it holds this vacuum, it's not leaking but if it loses vacuum, it's leaking. Also, make sure the tube that connects the MAP sensor to the ECM fits well and isn't leaking. It would tend to leak at the ends.
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  #18  
Old 09-29-2014, 11:00 AM
SenselessSteve SenselessSteve is offline
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Thanks Jim. I read another thread you had helped with and I tried the paperclip test. It flashed codes 14 and 21.

I'll try to google what they are now
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  #19  
Old 09-29-2014, 11:18 AM
SenselessSteve SenselessSteve is offline
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Also - there doesn't appear to be a tube that connects my MAP to the ECM and no place for one to go?? The plot thickens further.

Keep a suitcase packed Jim - you might get that trip to Ireland :-) thanks for your help
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  #20  
Old 09-29-2014, 11:57 AM
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Originally Posted by SenselessSteve View Post
Thanks Jim. I read another thread you had helped with and I tried the paperclip test. It flashed codes 14 and 21.

I'll try to google what they are now
21 is TPS High, 33 and 34 are MAP sensor and 14 is ECT High Temperature.

The MAP sensor attaches direct on the intake- look at this link for a rectangle on top with two screws, along the far edge of the flat surface. THAT's where your MAP sensor is supposed to mount and it doesn't use a tube. If the tube isn't connected and has no vacuum applied, the sensor is only reading barometric pressure and thinks the engine is running at WOT (Wide Open Throttle), causing a very rich condition.

How high the TPS reading is remains to be seen- open the throttle a bit and see if it idles- if it does, it's possible that a TPS from a regular engine was installed and that doesn't work. The LT-1 TPS is reverse and if the regular one is used, the ECM thinks the throttle is WOT and won't run. WOT during crank is how you would clear a flooded engine and no fuel is delivered at that time.

Ordinarily, 14 and 21 would result in a very lean fuel mixture (high temperature needs less fuel and if it runs lumpy, it may be in RPM Reduction, which others call 'Limp Mode', incorrectly. 21 may result in a default setting of 12%, which causes it to run, but not at its best. If that was the only code and situation, acceleration would be sluggish and it probably wouldn't achieve top speed.
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