Strange miss on 4.3 Volvo multi port, follows injector plug

[daleatskiworldorlando]

Hi all, I have a strange one.

2002 Volvo 4.3 GXI multi port fuel injected engine.

On lake test the boat seemed low on power and was running rougher then I would think a V6 should. The history of the boat is it has seen very little use with a lot of sitting so my first thought was check the injectors and see if any might be gummed up. All six are clicking at idle when I stick my long screw driver on the side of the injector and put it to my ear.

Next I tried speeding up the engine to about 1200 RPM to take it off of IAC and pulled each injector one at a time. Number 3 made no difference. All the rest would make a noticeable drop in RPM when pulled but not #3.

So I pulled the injector and tested it back at the shop. It was clear and working fine. Went back out to the boat and re-installed the injector in the spot for number 5 and put the injector that was at 5 in cylinder 3.

Re-started and the same problem, missing on 3. The spark plugs on the port side are hard to access so instead of checking the spark plug/compression I moved the wire that was going to injector 5 and put it on 3 and then put 3 on 5.

Now this is where it gets strange, the miss moved to cylinder number 5. It followed the injector plug. How does that make any sense? The injector was clicking the whole time. As far as I know this engine uses batch firing for the injectors so crossing the wires should make little difference. Cylinder number 3 was working fine with the crossed injector plug.

Anybody had an injector plug cause a dead cylinder but still click the injector?

Strange. Thanks, Dale

 

[thrasher]

Re: Strange miss on 4.3 Volvo multi port, follows injector plug

As far as I know the injectors are not connected in parallel, each injector has its own driver in the engine control unit (as they are all operated at different times (relative to crankshaft position)). From your description I would think you either have a problem with the controller for the injectors or a wiring problem between the controller and injector. I would expect that swapping the injector leads between cylinders 3 & 5 would prevent the engine from running correctly. I think you need to carefully check the wiring from the injector back to the control box. If you can't find a fault then I think it's time to take the boat to a shop that has the necessary tools to check the engine control unit..

Gary

 

[Maclin]

Re: Strange miss on 4.3 Volvo multi port, follows injector plug

As thrasher described it, Multi Port Injection systems fire each injector separately, timed to the intake stroke. You just proved that the problem is definitely in the #3 curcuit but that the injector itself is fine.

 

[daleatskiworldorlando]

Re: Strange miss on 4.3 Volvo multi port, follows injector plug

As far as I know the injectors are not connected in parallel, each injector has its own driver in the engine control unit (as they are all operated at different times (relative to crankshaft position)).

Hi Gary and the group, I think you are thinking of the 8.1 The 8.1 does have a driver for each injector.

When I wrote the messge above I did not think the 4.3 had the same setup as the 8.1. I had to check the wiring manual to confirm that the 4.3 instead uses batch firing. There are only two drivers in the ECM. One fires cylinders 1, 3 and 6 and the other fires 2,4 and 5. Because only one cylinder is having a problem and the other five are ok both drivers must be ok.

Things just do not add up. About the only thing that is left that I can think of is the wiring for injector plug number 3 may have more resistance in it then it should and I'm loosing injector pulses. The injector still fires but maybe not as fast or as many times as it should.

This is just one strange problem that I have not run across before.

Will try to remember to post a follow up if I ever figure this thing out.

Later, Dale

 

[JustJason]

Re: Strange miss on 4.3 Volvo multi port, follows injector plug

how are you isolating the cylinders to detect the miss? are you pulling the plug wire or are you using a kv meter?

 

[dcg9381]

Re: Strange miss on 4.3 Volvo multi port, follows injector plug

My experience is from custom EFI systems - not this marine stuff, so YMMV:
Almost all gasoline motors are batch fired - there simply isn't much to be gained by going to a sequentially injected system. There are sequentially injected systems, but they're pretty rare - reserved for Diesel and some of the lastest EFI systems.

It's normal to see injectors driven in banks. However, the banks probably will batch fire at the same time. There's no real easy way to check this - unless you've got an oscilliscope or a very detailed factory service manual.

As you've move the mis via injector plug, it sounds like you've found your problem.

Check this:
The injectors are either fired by pulsing to ground (in which case they'll have 12v between one of the plugs and a ground point) with the ignition on (not running)
or
They're pulsed high - in which case you'll get 12v between one side of the plug and positive. (ignition on, not running)

I've seen cases where there are 2 injector banks, but the banks are tied together in the wiring harness.

If the injectors are seperate, but they're on the same bank - check for continuity between the injector plugs... I'm expecting for your injector plugs to have continuity across plugs on the same bank, with the exception of the one that isn't firing.. In that case, it's probably a crimped or bad wire somewhere - hard to find without a signal/tone generator.

To "patch" it, you could run off any other injector on the same bank, wiring in parallel... To fix it you'll have to trace that wire back... As mentioned, I'd do it with a tone generator so you don't have to gut the harness.