Logo
FULL SITE MENU

8.1 GXi-f conundrum; power under load

R

red_georgia

Member
Have quite a perplexing issue. Boat is a 2006. Never had a engine running problem before. On the lake this weekend, during first few hours, noticed I was struggling to get on plane (taking 3 times as long as normal) and seemed to be lacking power. Once on plane, could only get to about 3K rpms. Stopped for lunch. After lunch about 20 miles+ from home, could NOT get on plane. Could not get motor to accelerate past 1500rpms and anything above 1000 the motor was shaking pretty bad, and occasional backfire and sounded like running really rough with potential mis-fires. Assumed I was in limp mode and we crawled all the way back for 3 hours at 9-10 miles per hour.

Having replaced a bad fuel pump two years ago, I was guessing the cheap Chinese one I bought was failing again. Got fuel pressure test kit on it and it passed both key on, no load, and loaded tests with fuel pressure staying 40-45psi the entire time. When under load in water, same motor defect conditions exist even though fuel pressure is within spec.

Ordered Marine Scan tool which I put on it this morning. NO DTC's other than high voltage on trim sending unit. Trim gauge hasn't worked in 15 years so I'm guessing that isn't the problem. When running, it is not over heating, oil pressure is fine, and the two parameters for engine derate are both off. When in neutral, or in gear but just spinning air, motor runs normally and accelerates to 3K RPMs with no problems (just spinning air so didn't push it higher). Motor not vibrating, acceleration is smooth, and TPS demand and output looks correct on scanner.

So, take it back to water, with scanner connected and same defect condition under load occurs. Motor shakes, struggles to go past 1,500 rpm and sounds terrible. Hi idle without load still revs correctly in the water.

So, I'm stuck.... with no codes and running fine without load, doesn't it have to be the outdrive? Under load potentially eating itself/binding and overpowering the motor trying to turn it? I'm going to drain outdrive tomorrow and look for glitter/water but what else could it be?

Perplexed?????
 
No load 'rev capability' doesn't mean much...

The ECM doesn't monitor everything and what it does check is limited...so there can be a problem or two and the ECM will never set a code.

Following the suggestions will get you to a happy place sooner...
 
AllDodge said:
The Techmate manual shows how and that it is done under load
Click to expand...
Referring to the tech mate pro manual, I assume the injector balance test is the “injector fire test” in manual. There isn’t a “misfire” test so are you calling for the “spark kill test” which requires it be done under load?
 
AllDodge said:
Yes, I'm a Merc guy so I remember their terminology more
Like Merc's slave relay and VP start assist relay
Click to expand...
Ok, ran the injector fire test x2 to confirm values:

1: 42/36
2: 42/30
3: 42/34
4: 42/30
5: 42/30
6: 42/38
7: 42/36
8: 42/33

Not clear to me if 2-4-5 are correct or the other ones or next steps?
 
Looks like your in need of a clean and flow testing on a bench for the injectors, but this shouldn't cause the problem you have now
 
AllDodge said:
Looks like your in need of a clean and flow testing on a bench for the injectors, but this shouldn't cause the problem you have now
Click to expand...
Thanks. Have it in water on trailer for load. Spark/injector kill results the same. Cylinders 1/3/6/7 are not firing. No change in engine rpm/noise when shutting those cylinder down.
 
red_georgia said:
Thanks. Have it in water on trailer for load. Spark/injector kill results the same. Cylinders 1/3/6/7 are not firing. No change in engine rpm/noise when shutting those cylinder down.
Click to expand...
Going to swap coil on cylinders 1/2 and see if the fault follows to cyl 2. If yes, I’ll order coils. Only about 6 trips on the pugs so I’m assuming no problem there.
 
red_georgia said:
Going to swap coil on cylinders 1/2 and see if the fault follows to cyl 2. If yes, I’ll order coils. Only about 6 trips on the pugs so I’m assuming no problem there.
Click to expand...
This is a good test

The pics are for the wiring of the coils. Each bank has it's own harness which are the same but are driven by the PCM for different pins. If might be a bad connection but swapping the coil should provide good instight

496 Bank coil harnes.JPG
496 coil driver.JPG
 
AllDodge said:
This is a good test

The pics are for the wiring of the coils. Each bank has it's own harness which are the same but are driven by the PCM for different pins. If might be a bad connection but swapping the coil should provide good instight

View attachment 36202View attachment 36203
Click to expand...
Thank you….had to watch some football today, will continue the adventure tomorrow morning. Killing me today, while I was on ramp testing, probably 25 boats launched around me at 10 am to spend day on lake. I pulled out to make room and guy asked me….”why pulling out? U r supposed to be launching…”. I said, “boats broke…..enjoy the day!” Lol….
 
AllDodge said:
This is a good test

The pics are for the wiring of the coils. Each bank has it's own harness which are the same but are driven by the PCM for different pins. If might be a bad connection but swapping the coil should provide good instight

View attachment 36202View attachment 36203
Click to expand...
So…..I have a saying: “It can never be easy”. This challenge seems to be the case. Swapped coils on good/bad cylinder and no change. #1 cylinder still dead. I’m going to check plugs next but since they are fairly new, I doubt that is it. Seems to be upstream of coils. Not sure where to go from here.
 
red_georgia said:
Thank you….had to watch some football today, will continue the adventure tomorrow morning. Killing me today, while I was on ramp testing, probably 25 boats launched around me at 10 am to spend day on lake. I pulled out to make room and guy asked me….”why pulling out? U r supposed to be launching…”. I said, “boats broke…..enjoy the day!” Lol….
Click to expand...
One additional thought on condition is that the symptoms seemed to get progressively worse from morning to afternoon (had more power in morning than afternoon) which makes me think it is not a bad ground or bad wire. Is that logical thinking?
 
Could be the Ground (pin A and splice) or 12V (Pin H or splice 105), most likely not 5V (pin E)

Turn key ON and measure to see if you have 12V on Pink wire (Pin D) of each coil, and also 5V on Brown wire (Pin E) just for S's and giggles
 
AllDodge said:
Could be the Ground (pin A and splice) or 12V (Pin H or splice 105), most likely not 5V (pin E)

Turn key ON and measure to see if you have 12V on Pink wire (Pin D) of each coil, and also 5V on Brown wire (Pin E) just for S's and giggles
Click to expand...
On both a dead cylinder and a working cylinder the pink wire at coil plug is getting 11.7 v upon key on (a little low due to connection I'm guessing as getting a probe in those mini fittings required some creativey). The voltage drops to zero about same time fuel pump shuts off even thought key is left on but not started.

The brown wire was getting about .2V upon key on for both cylinders but also returned to zero when fuel pump shut off.

I would think the dead cylinder wouldn't be getting the 12v at coil but it is.....???? I didn't do every coil as I didn't want to poke every wire or potentially damage the connectors with probe. Figure same conditions exist in both banks cause I tested one on each side of motor, one being working and one not.
 
Don't poke the wire, you can disconnect the plug and measure direct

11.7V is not good, but could compare with cylinders that are firing

I would assume the 5V should stay up but maybe it doesn't. The issue is what are the differences between those that do work and those that do not? The issue is 5V should be everywhere that is needed and doesn't change. Like check other sensors and it should stay up.

I'm hoping it's a bad connection and not the coil driver in the ECM has burned out
 
AllDodge said:
Don't poke the wire, you can disconnect the plug and measure direct

11.7V is not good, but could compare with cylinders that are firing

I would assume the 5V should stay up but maybe it doesn't. The issue is what are the differences between those that do work and those that do not? The issue is 5V should be everywhere that is needed and doesn't change. Like check other sensors and it should stay up.

I'm hoping it's a bad connection and not the coil driver in the ECM has burned out
Click to expand...
I had the connectors off the coils but since the 12v is only present when key first turned on, then was going away I was struggling to confirm I was making a connection. Finally stabbed one wire and cycle key and figured out the 12v goes off if motor doesn’t start.

What is the 5v signal for? Usually the sensors send 0-5v so not sure I understand what the 5v is supposed to be doing at the coils.

In any case, there is no difference between working and non working cylinders at the coils.

Also, since failure of the ECM seems to be uncommon, what is chance it is Crank Position Sensor preventing the ECM from sparking those 4 cylinders even though no code is set?
 
Don't know for sure but the 5V is there to let the ECM know if a coil is not firing

12V should not go away because it comes from the main power relay (see bottom pic post 19). Might be the MPR is the issue but if that was it there should be other codes due to ECM is powered by it also
 
AllDodge said:
Don't know for sure but the 5V is there to let the ECM know if a coil is not firing

12V should not go away because it comes from the main power relay (see bottom pic post 19). Might be the MPR is the issue but if that was it there should be other codes due to ECM is powered by it also
Click to expand...
Since I’m running out of “obvious things to check” I’m going to try the crank position sensor as there are reports of it causing these symptoms without throwing a code. Open to other ideas. Have inspected all the harness, connectors, grounding block, etc and find nothing concerning
 
Have the crank sensor out and waiting on replacement.... then noticed something. On the injector balance test (results below), the cylinders with the low pressure drop across the rail, happen to be the same cylinders that are dead (1,3,6,7). Is it possible that the injectors aren't dispensing enough fuel to fire? 6-8psi drop during test but the working cylinders dropped 9-12psi, with 3 of 4 being at 12 psi?

1: 42/36
2: 42/30
3: 42/34
4: 42/30
5: 42/30
6: 42/38
7: 42/36
8: 42/33
 
red_georgia said:
Have the crank sensor out and waiting on replacement.... then noticed something. On the injector balance test (results below), the cylinders with the low pressure drop across the rail, happen to be the same cylinders that are dead (1,3,6,7). Is it possible that the injectors aren't dispensing enough fuel to fire? 6-8psi drop during test but the working cylinders dropped 9-12psi, with 3 of 4 being at 12 psi?

1: 42/36
2: 42/30
3: 42/34
4: 42/30
5: 42/30
6: 42/38
7: 42/36
8: 42/33
Click to expand...
red_georgia said:
Thanks. Have it in water on trailer for load. Spark/injector kill results the same. Cylinders 1/3/6/7 are not firing. No change in engine rpm/noise when shutting those cylinder down.
Click to expand...
The injector balance test is just telling you the injectors are wearing out/plugging up. Don't think it has much to do with current problem.

At this point I can't tell if you don't have spark or fuel on Bank 1

The spark and injector tests are 2 separate tests. What one did you do? If you did both with the same results -- time for a compression test.

To test for power and ground at the coil. Use sewing needles or pins clamped to the DVM leads. Red lead in cavity D = pink wire, Black lead in cavity A = black wire.
KOEO, techmate connected. Now use the Relay test in the ECM tests section to turn on all the relays and you have a couple of seconds to get your reading, write it down and then test the other 7 coils the same. Now you don't need a helper or run back and forth to the key!

Do Not probe cavities B or C, DVM readings are meaningless on these wires. Brown wire? I don't see a brown wire in the wiring diagram for this engine.

The 5 volt reference doesn't have anything to do with the coils. Just uses 5 v ground as part of monitoring the firing of each coil.

There are NO DTCs for the ignition system on this engine.
 
Back
Top