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8.1 GXi-f conundrum; power under load

muc said:
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.
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Thanks, will do and report back. Need to get crank sensor back in tomorrow and working on eliminating rest of fuel system right now. Struggling to get pick up tube /fitting out of tank. Soaking in PB blaster right now.
 
muc said:
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.
Click to expand...
And, ran both injector kill test and spark kill test with same results. No change on the four dead cylinders. As for compression test, there are almost zero internal failures on the 8.1l block before 259-300k miles. I’m no where close to that and oil changes/etc have been annual. The problem got worse over time so I’m confident it is not internal rotating assembly problem.
 
red_georgia said:
And, ran both injector kill test and spark kill test with same results. No change on the four dead cylinders. As for compression test, there are almost zero internal failures on the 8.1l block before 259-300k miles. I’m no where close to that and oil changes/etc have been annual. The problem got worse over time so I’m confident it is not internal rotating assembly problem.
Click to expand...
Ya, I didn’t think the compression thing through. You should run a spark gap test to see what’s missing. Fuel or spark.
 
red_georgia said:
And, ran both injector kill test and spark kill test with same results. No change on the four dead cylinders. As for compression test, there are almost zero internal failures on the 8.1l block before 259-300k miles. I’m no where close to that and oil changes/etc have been annual. The problem got worse over time so I’m confident it is not internal rotating assembly problem.
Click to expand...
Ok, breaking out the multi-meter next but using a timing light and a noid light for the injectors, I've verified one of the dead cylinders is getting both a spark pulse and an injector pulse. Doesn't that have to mean that it is a plugged injector that isn't spraying or spraying correctly preventing cylinder from firing?

Also, i'm guessing one of the injectors is leaking as the fuel pressure drops 1-2psi every 10 minutes eventually goes to zero after key shut off.

BTW, new crank sensor is in and has no impact. The more I've researched the more I'm convinced it is a fuel issue. I've replaced fuel filter, fuel hose, anti-siphon valve and now trying to check tank/pickup tube but the pickup tube is stuck in the sealant applied 20 years ago. AND....the idiot that put it together cross threaded the anti-siphon valve so when I took it out, the aluminium threads on it are destroyed and the pick-up tube fitting is damaged also. I will replace if I can get it out or clean up the threads with a tap. 3 days of PB Blaster aren't cutting the sealant so now using Acetone/ATF.....any other ideas?
 
red_georgia said:
Ok, breaking out the multi-meter next but using a timing light and a noid light for the injectors, I've verified one of the dead cylinders is getting both a spark pulse and an injector pulse. Doesn't that have to mean that it is a plugged injector that isn't spraying or spraying correctly preventing cylinder from firing?

Also, i'm guessing one of the injectors is leaking as the fuel pressure drops 1-2psi every 10 minutes eventually goes to zero after key shut off.

BTW, new crank sensor is in and has no impact. The more I've researched the more I'm convinced it is a fuel issue. I've replaced fuel filter, fuel hose, anti-siphon valve and now trying to check tank/pickup tube but the pickup tube is stuck in the sealant applied 20 years ago. AND....the idiot that put it together cross threaded the anti-siphon valve so when I took it out, the aluminium threads on it are destroyed and the pick-up tube fitting is damaged also. I will replace if I can get it out or clean up the threads with a tap. 3 days of PB Blaster aren't cutting the sealant so now using Acetone/ATF.....any other ideas?
Click to expand...
Doesn't that have to mean that it is a plugged injector that isn't spraying or spraying correctly preventing cylinder from firing?
No that's not what this means, the injector balance test you did shows that injector is flowing fuel. Is it flowing the correct amount with a proper spray pattern? Further testing would be required.

but using a timing light
I highly recommend AGAINST using a timing light to check for spark! What can happen is that the timing light will detect voltage, but there isn't enough voltage to spark the plug. So the light flashes but the plug doesn't spark. You have now used an invalid test and possibly will make a bad opinion based on this. It is always advised to use a spark gap tester to test for spark for this reason.

That's a very small leak and wouldn't have anything to do with the current issue.


BTW, new crank sensor is in and has no impact.
Some of the early marine 8.1s had issues with the crank sensor. But that issue was corrected before your engine was built.

The more I've researched the more I'm convinced it is a fuel issue. Can I ask why?
You don't have spark on 3 or maybe 4 cylinders? And you want to guess at fuel without doing some of the easiest and cheapest tests first?
 
muc said:
Doesn't that have to mean that it is a plugged injector that isn't spraying or spraying correctly preventing cylinder from firing?
No that's not what this means, the injector balance test you did shows that injector is flowing fuel. Is it flowing the correct amount with a proper spray pattern? Further testing would be required.

but using a timing light
I highly recommend AGAINST using a timing light to check for spark! What can happen is that the timing light will detect voltage, but there isn't enough voltage to spark the plug. So the light flashes but the plug doesn't spark. You have now used an invalid test and possibly will make a bad opinion based on this. It is always advised to use a spark gap tester to test for spark for this reason.

That's a very small leak and wouldn't have anything to do with the current issue.


BTW, new crank sensor is in and has no impact.
Some of the early marine 8.1s had issues with the crank sensor. But that issue was corrected before your engine was built.
The more I've researched the more I'm convinced it is a fuel issue.
You don't have spark on 3 or maybe 4 cylinders? And you want to guess at fuel without doing some of the easiest and cheapest tests first?
Click to expand...
I'm still working on it to verify. I already swapped coils and plugs from good to bad cylinder with no change. I did test signal to coil this morning and both good and bad cylinder were 12.2V. One thing I haven't tested or swapped was wires. on a good and bad cylinder, only getting 2.03K and 2.3K ohms on the two plugs. That is low as I understand it? Something as simple as plug wires would be nice.......

Can you explain what the spark gap tester is?
 
red_georgia said:
I'm still working on it to verify. I already swapped coils and plugs from good to bad cylinder with no change. I did test signal to coil this morning and both good and bad cylinder were 12.2V. One thing I haven't tested or swapped was wires. on a good and bad cylinder, only getting 2.03K and 2.3K ohms on the two plugs. That is low as I understand it? Something as simple as plug wires would be nice.......

Can you explain what the spark gap tester is?
Click to expand...

Looked up that spark gap tester..... have one coming from amazon.
 
red_georgia said:
Plugs are 2 years old and have about 10 hours run time on them. Wires I tested are about 18” long so definitely low. Wires are 20 years old.
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So just used the spark gap tester and it is definitely sparking. The one I got is adjustable and it would carry the spark all the way out to 3.5cm. Spark is a single solid white line. Very hard to see the line/color when tester is closed to normal spark plug gap. Just to reiterate, have swapped coil and plug from good to bad cylinder with no impact. I am waiting on plug wires to arrive.... oddly enough, live in one of the largest boating towns in country and none of like 6-7 Marine Dealers stock volvo parts.... only mercury so I had to order. That being said, with the spark gap test showing positive spark, and new wires coming in a few days, if still not firing doesn't it have to be the injectors?
 
Resolved. Here are the details in case it helps anyone searching this problem in future. Recap:

1. Volvo penta 8.1L experience power loss over a period of weeks culminating in the inability to accelerate past about 1K rpms/9-10 mph at basically idle. Severe misfire and backfires when trying to apply power.
2. Scan showed no ECM fault codes stored. No Alarms.
3. Spark Kill test and Injector kill test via tech mate pro marine scan tool indicates 4 dead cylinders.
4. Fuel pressure gauge indicates fuel pressure at rail is within spec at idle, at speed, and under load.
5. Throttle position sensor reading normal and throttle body is working properly so not an air problem.
6. Verified 12v signal to coils using vm. Also swapped good coil to dead cylinder with no change.
7. Verified spark at dead cylinder using in line spark gap test tool.
8. Verified ECM is sending injector pulses to dead cylinder using noid light tester.
9. Injector balance test via tech mate pro shows steady/consistent drop of 12psi at rail across the four good cylinders using 100ms pulse. The four dead cylinders were inconsistent and showing only a drop of ~5-7 psi. So clearly inconsistent fuel delivery. In the string above you see many comments about how this should not be causing my symptoms however that was not the case. While the injectors were flowing fuel, it was not sufficient nor properly atomized to enable combustion.

After driving myself nuts ruling out everything else. And changing the "crank position sensor" just in case.... Had no choice to go further down the path of injectors. Fortunately there is an injector service shop very close to me. Pulled the injectors and sent them to them. Their balance test confirms 4 flowing inadequate volume of fuel with improper spray pattern. They use an ultrasonic cleaning process and cleaned them and replaced lower o-rings. Post cleaning, balance test shows perfectly atomized spray and completely equal volume of fuel for each injector. They had them back to me in 24 hours. Cost of service was $200.00 for 8 injectors. Reinstalled them and during startup could immediately tell I was back at full power just from sound at start up. Put motor under load and ran spark kill test and verified all 8 cylinders are firing.

With the boat being 20 years old, and the fact that two years ago it sat for two years without running while I was working in another state, I should have been quicker to go after the injectors. In hindsight, I should have used the inline spark gap tester first to verify spark on dead cylinder, then after noid light confirmed injector pulse, I should have pulled the injectors and gone for the cleaning due to the results of the original balance test. Could have had it fixed in one day. Hope this helps somebody!
 
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