Not your typical Limp Mode....

[sea2sky]

I'm quite familiar with engines, but this one has me stumped. I have read all of the threads on limp mode, but this one is different...

I just bought a 2006 Tige 22i with the 5.7L 340HP Vortec engine. ECU model is TMD1-160G1 403-000078. It appears I have an MEFI 4 system.

The alarm sounds (continuous) on iginition start up and then stops. All gauges work, except for the speedometer (possible the transducer? All gauge readings are within range.

The Problem:

The engine starts every time, and runs fine at idle. I can engage the transmission, and slowly throttle up to ~2500rpm, where the engine goes into limp mode and throttles b1ack to idle. The throttle will not increase again, until I turn off the ignition and start the boat again. If I put the boat in neutral, I can throttle up slowly to rev limiter ~5200rpm. If I throttle up quickly in either drive or neutral, it goes into Limp mode. Same results in forward or reverse. There is no loss in boat power, until limp mode.

I do have the dual battery system. 1 is a brand new battery, the other older one has been charged and load tested at a parts store.

I do not hear any alarms at all while limp mode is engaged.

No thread on here describes how to isolate the two batteries to prevent limp mode? I can at least start there. Any other suggestions, all are appreciated.

[sea2sky]

Pictures of wires

I also forgot to add that there are several wires that are disconnected. Not matter what configuration I hook them up in, the results are still the same - limp mode.

Pic 1 has 3 pairs of wires. 1 pink wire, 3 brown/white wires, and 2 DarkBrown/white wires. These are located on the top rear left of the engine.

Pic 2 has 2 connectors (not matching), and one white wire. These are located on the top middle of the engine.


Pic 3 has a single brown/wite connector located by the starter on the right side.

Any idea the configuration of the wires? I have the manual, but am unable to trace them.

[dom w. forte]

If the boat was oringinally equiped with dual batteries there was an issue with the 2 computors getting out of sink with comunications because of voltage differences , the fix was to wire both ecm and tach module to the same power, if after the rewire, problem still exsists then shifter or pps is at fault.
When scanning data will trip code 81 which is a DBW code, suggest you scan first.

[sea2sky]

Thanks Dom. Is rewiring to the same battery a matter of pulling one cable from the accessory battery to the starter battery, or do I need to pull wires from the engine. I'm fine with re-soldering or running wires, just not sure which wire needs moving? I don't have acces to any scanner other than a OBD1/2 scanner. Boat dealer has at least a week wait list (of course long weekend us upon us).

[dom w. forte]

The rewire is more difficult and requires that the power box on top of the engine be openned ,the ground and power wire from the tach module which is wired up at the dash has to be run into the box and hooked to the same relay which powers the engine ECM, this requiers a schematic of the harness.

[sea2sky]

Thanks again Dom. That seems easy enough to do. I can figure out which + and - feed from the ECM relay on top of the engine.

Any chance you have a schematic or color of wires to swap at the tach? Or is there only one + and - feeding into the tach at the dash? (two connectors on the tach) The Marinepower schematic seems to only reqire a +, _, and tach signal - correct?

Is it an issue that the speed sensor isn't reading?

[sea2sky]

I connected the entire system to one battery, to try and eliminate and voltage difference. Still the same result - limp mode after quick acceleration. No alarm.

[dom w. forte]

Im not talking about the tachometer in the dash, Iam talking about the tach module which is a computor which controls the DBW system , if this is a v drive boat the module is ussually behind the rear seat when you open the engine cover.
When DBW came out every company was useing mefi 4 engine computor, so they added a 2nd computor for the throttle control called tach module, when you move the shifter the pps request acceleration to the tach module, through serial data the tach module talks to the ecm , so when you have 2 computors on 2 different power sources and there is a .2 volt difference they dont comunicate and go into limp mode.
All engine companys had this problem the first year, the next year introduced mefi 5 ,1 computor did the whole job no problem.

[bigdaddy_houseboater]

Threads like this actually make me glad I bought the carb boat with no computer.

[sea2sky]

Im not talking about the tachometer in the dash, Iam talking about the tach module which is a computor which controls the DBW system , if this is a v drive boat the module is ussually behind the rear seat when you open the engine cover.
When DBW came out every company was useing mefi 4 engine computor, so they added a 2nd computor for the throttle control called tach module, when you move the shifter the pps request acceleration to the tach module, through serial data the tach module talks to the ecm , so when you have 2 computors on 2 different power sources and there is a .2 volt difference they dont comunicate and go into limp mode.
All engine companys had this problem the first year, the next year introduced mefi 5 ,1 computor did the whole job no problem.

It's a 22i. I think I understand. I have the PCM module on top of the engine, with 2 connectors for the MEFI4 system. I then have another DBW module - it's located to the bottom left of the front of the engine. One connector goes to the TPS at the helm, and the other connector goes to the engine. It is this module that requires rewiring?

I also pulled apart the TPS - it had water in it. Unfortunately when I put it back together, I now get nothing but limp mode right from start (possible because I moved the set screw?). If the TPS is off slightly on startup, can it throw the engine into limp mode? (How sensitive is throttle position on startup?) I understand there is a procedure to use a voltmeter to adjust the TPS position on the throttle assembly?

Thanks again.

[dom w. forte]

On the shifter there is a pps, in side that sensor is actuatly 2 sensors, because everything has to be redundant, when you move the throttle you are requesting acceleration to the tach module, it in turn through serial data tells the ecm to move the throttle motor, when the throttle moves there is 2 tps sensors in with the motor they send back to the ecm there position , if any one sensor is off or glitches it will go to limp mode, this is a major safey area.

[sea2sky]

Dom, thank you very much for your support. In the end, it was the TPS. Due to the moisture in the TPS, it would create a short in the carbon tracks, the ECM would see this as an out of range reading, and cause a limp code. For others, the TPS is quite easy to pull apart and clean - these are pretty bullet proof, and you might just save yourself having to order a new one (temp fix if you're in a panic).

[sea2sky]

I still don't know how to connect the loose wires in the pictures, so if you do know, please tell me. Thanks.

[sea2sky]

So I haven't completely solved this. I took it in to get scanned. Turns out the computer is throwing a PPS code. The ECU is not reading any signal from the TPS, despite the throttlebody still operating. Mechanic says its:

1. ECU
2. Throttle control computer
3. TPS - I already inspected this when I pulled it apart.
4. Throttle body solenoid and sensor - it's riveted together though, looks like a single unit?

Any ideas?

[chpthril]

So I haven't completely solved this. I took it in to get scanned. Turns out the computer is throwing a PPS code. The ECU is not reading any signal from the TPS, despite the throttlebody still operating. Mechanic says its:

1. ECU
2. Throttle control computer
3. TPS - I already inspected this when I pulled it apart.
4. Throttle body solenoid and sensor - it's riveted together though, looks like a single unit?

Any ideas?

Why didnt the guy that scanned it...... diagnose it? A simple pin-out of the TPS with a DVOM would have been worth its weight in gold.