Spark Plug question.

[BILLDON]

I bought my boat with a 1999 V.P. 5.0 GI PEFS two years ago and I've replaced the spark plugs twice now. Engine now has 475 hours on it. I bought a set of 8 plugs from the V.P. dealer this year that appear to be iridium (expensive). When I first took out the plugs after the first boating season, the 4 plugs that are on the "corners" of the V-8 setup looked fine, tan color, no carbon, etc. The 4 "inner ones" were all fouled up with black carbon. Ditto after this past season. The Manual goes to great lengths to say I should change the plugs every season, and explains in "too much detail" how to clean carbon off the plugs. Is this a common situation? I suspect that the TBI injector system, with two injectors in the throttle body, probably doesn't work as well as a system using 8 separate fuel injectors. I am wondering if there is something in my engine that needs to be repaired/replaced (like my injectors)? Having said all that, I think the engine runs fine, starts right up etc. Any thoughts would be appreciated.

 

[Fun Times]

Re: Spark Plug question.

I am wondering if there is something in my engine that needs to be repaired/replaced (like my injectors)? Having said all that, I think the engine runs fine, starts right up etc. Any thoughts would be appreciated.

Hi there Bill, While this type of problem would be an challenging diagnostics for just about anyone especially time wise as to try and figure out as to why it's keeps on doing this, I don't believe there would be an easy answer to provide you. And ultimately it could end up being the characteristics of the system vs maybe how you use the boat overall.

There are quite a few steps diagnostic wise to take with trying to locate something like this from checking to see if the fuel pressure is within specifications, fuel injector pulse width is timed right, fuel injector spray pattern is right, are the fuel injectors leaking, should they be cleaned professionally to be inspected for fuel flow accuracy, correct spacers & gaskets for the TBI unit to intake manifold, ECM calibrations within normal range, Are all the sensors in normal operating range for your engine model, is the fuel pump module working correctly, is the timing set right and advancing correctly, engine temp running normal and getting to temp within normal time frame, spark plug wires are in good shape and ohms check out good, what fuel octane do you use vs what is recommended, compression check to see if you have higher compression in them cylinders due to excessive carbon buildup, try cleaning out the carbon buildup if there is any, is the 12 volt power and ground system is working 100%, since your using iridium spark plugs did they come pre gapped to your needed settings for your engine model or did you have to re-gap them? Iridium plugs are easily damaged during the gapping process and not really recommend by the plug manufactures but can be done if careful.

Probably missing a few steps somewhere in there but that is the jiff of where to start with a running condition like this.

All that said, we are here to help the best we can if you decide to tackle the problem?

 

[BILLDON]

Re: Spark Plug question.

Thanks for all the info. I have thought a lot about this and think that the fuel injectors are giving off too rich a fuel/air mixture, but not too much. The rich fuel maybe is reaching the closer in cylinders but not the outer ones? Almost all of the other items you mention have been checked out and are all OK. As to the iridium plugs, the past two seasons have been on the regular plugs, I just replaced them this past week with the expensive ones from the dealer ($96.00 for 8, in a Volvo Penta box, Alaska prices). I should stress again that the engine runs very well and starts right up so I am hesitant to launch off on a witch hunt. It's just a situation that puzzles me and was wondering if anyone else has noticed anything like this. There have been lots of people looking at this but yours is the only reply so I guess it's an unusual thing.

 

[Fun Times]

Re: Spark Plug question.

I have thought a lot about this and think that the fuel injectors are giving off too rich a fuel/air mixture, but not too much. The rich fuel maybe is reaching the closer in cylinders but not the outer ones.

If you do a "Google search" of 1999 V.P. 5.0 GI PEFS runs rich, there area few threads from here and other forums that mentions running rich. Not sure if you'll find something such as your exact problem but it may give you some other ideas to consider.:noidea:

There are a number of places if you look online that you can send your injectors off to and have them both checked and cleaned at the same time as a starting point if interested.

Good luck.

 

[JoLin]

Re: Spark Plug question.

Sometimes it's a lot easier to just live with a chronic but non-threatening condition, than it is to cure it. Apparently the plug fouling isn't serious enough to affect the way the engine runs, and your dealer is making a good buck selling you iridium plugs that foul up anyway.

If it were me, I'd be testing whatever I could without spending a ton of money on it. If I couldn't find anything wrong, I'd live with it until the offending component causes running issues, if it ever does. There really shouldn't be any need to replace all the plugs annually in a modern engine.

Given that your issue is limited to 4 of the cylinders, I might go so far as to annually swap the non-fouled plugs INTO the 3-4-5-6 cylinders and only buy 4 new ones to replace those. They wouldn't be iridium plugs, either.

My .02

 

[Volphin]

Re: Spark Plug question.

That's a lot of cash for an old chevy engine spark plug set! AC Delcos will work just fine. It's always better to be a little rich than too lean.

 

[Maclin]

Re: Spark Plug question.

My experience concurs what Volphin wrote, rich is safer in "legacy" carbed Marine Duty Cycle engines. My Marine V8 4bbl Holley carbed engine sparkplugs always look dark tan and a little sooty, but they have not fouled ever (or yet) during their tenure. I replace them every 3 years or so, and go with just plain old single electrode sparkplugs, no special materials.

 

[BILLDON]

Re: Spark Plug question.

Thanks for all ideas. I have the maintenance records for all work done on this engine since the boat was re-powered in 2001. Every Fall, the P.O. put in new plugs. The manual's "checklist" for this engine has the spark plug box checked for "replace once per season." I think I am going to just live with this problem (non-problem) until (if) something else goes wrong (i.e. if it ain't broke, etc..). And Volpin, FYI, the $96.00 plugs came in a blue Volvo Penta box but said: "AC Delco" on them! I have a 2004 Toyota Camry with 146,000 miles and it still has the original spark plugs in it. I think that these old chevy engines were designed to be run at 2000 RPM. I run my engine at 3500 RPM typically (so did the P.O.). This might have something to do with it.

 

[Volphin]

Re: Spark Plug question.

I can FedEx ya a case of AC Delco MR43LTS cheaper. LOL Marine plugs, regardless of what the manual says, have no need to be changed every season. The plug doesn't care if it runs at 4800RPM or idle. It's the engine hours, not the rpm.

I miss Alaska. I almost didn't leave the last time I visited.

 

[JoLin]

Re: Spark Plug question.

I think that these old chevy engines were designed to be run at 2000 RPM. I run my engine at 3500 RPM typically (so did the P.O.). This might have something to do with it.

You must be young

Those SBC's were designed back in the day when cars had 2- and 3-speed trannies, 3.-something final drive ratios and little tires. They ran at over 3,000 rpm continuously anytime you hit the highway. I still find it a little odd to be doing 70 mph and see only 2000 rpm on the tach.

And for the record, we ALL run them at over 3000 rpm's in our boats. That's how you get and stay on plane.