Volvo Penta 5.0GI Running Rich

[evantful]

Hi all,

I have 1999 Volvo Penta 5.0Gi (PWTR series engine, Throttle Body Injection) with 634 hours. For the last 2 seasons its been running rich causing a blackish film on the transom and a increase in fuel smell idling, after about 15hrs on an oil change I can begin to smell fuel in the oil.

It does run virtually without issue. Starts right up, idles well (never stalls or dies, but I do notice it missing) and can run up to WOT and anywhere in between perfectly. So while I probably should just be happy and keep boating, it does continue to bother me.

So far I have done the following 2 years ago:
1. Replaced Cap and Rotor
2. New OEM Volvo Plug wires
3. New MAP and Engine Coolant sensors
4. New PCV
5. New IAC
6. New Plugs (done seasonly in the spring)

This spring the following was done:

1. Fuel Pressure test
- Low side 5psi
- High side 29.5-30psi idle
Both are almost dead on spec.

2. Compression test
- Engine run to operating temp, Plugs out, throttle wide open, fuel system disabled, ignition disabled. All cylinders were 182psi-189psi

So what I did notice when I pulled the plugs (which were brand new and only run for about 45min-1hr idling-1300rpm on muffs) to do the compression test is that 3 of them were much more fouled, while the other 5 looked just fine.

Here are two pictures of the plugs, plugs are in order,
The first is the Port side and the second is the Starboard Side. Left most plugs are the Front cylinders, Right most are the rear cylinders.

Any thoughts on where I should go forward? Im thinking of checking the ignition system, given that only 3 plugs seem to be much richer. Would a leaky injector be able to do that?

 

[BarryTurano]

I have/had (had because it is no longer injected) the same motor with the same problem and about the same number of hours. Problem was never located. I am sorry this will not be much help. I wound up taking the throttle body off and replacing it with a carb. Also changed the entire distributor, took out the computer and sensors. If you search back on this site you will find pages of what I went through. Still have minor intermittent WOT issues. Hope to have that settled tomorrow with a new fuel pump. Sorry I have been no help but if your problems continue do what I wound up doing. Just don't drop over $8000.00 before doing it. The mechanic I was using was a "parts changer" not a mechanic even though he claimed to be one.

 

[evantful]

I actually do remember your thread from a while back I found it in my research. If it ever gets to that point I may follow you with a Carb setup.

Right now the engine does run virtually without issue. Straight up to WOT without any hesitation and can idle for long durations without bogging or stalling out.

The main thing I want to tackle now is those three plugs and why they are fouled compared to the other five.

 

[ericga]

So what I did notice when I pulled the plugs (which were brand new and only run for about 45min-1hr idling-1300rpm on muffs) to do the compression test is that 3 of them were much more fouled, while the other 5 looked just fine.

Any thoughts on where I should go forward? Im thinking of checking the ignition system, given that only 3 plugs seem to be much richer. Would a leaky injector be able to do that?

Yes leaking injectors could do that. Are the injectors spraying a nice conic shape with no dripping?

 

[bruceb58]

Instead of doing a plug read after idling, pull the same plugs after a long hard run and don't let the engine idle before you pull them.

 

[dypcdiver]

Have you checked the temperature that the engine is running at? I had asimilar problem that turned out to be a blocked bypass in the thermostat housing causing the engine to run at 135/140F and making the ECU over fuel because it thought it was a cold engine and required (choke).

 

[evantful]

Yes leaking injectors could do that. Are the injectors spraying a nice conic shape with no dripping?

For the most part the pattern seems nicely conic in shape, it does seem to be slightly better looking with throttle applied.

With this being a TBI fuel Injection system (two injectors mounted at the throttle body intake) could that still lead to 3 specific cylinders running rich? It seems the rear most cylinder on each side are by far the worst offenders. I also compared the plugs from the last year, the same three cylinders had heavy rich plugs.

 

[evantful]

Have you checked the temperature that the engine is running at? I had asimilar problem that turned out to be a blocked bypass in the thermostat housing causing the engine to run at 135/140F and making the ECU over fuel because it thought it was a cold engine and required (choke).

Based on the tach gauge the engine is warming up to operating temp fine. I don't have a scan tool to get direct read out from the ECT.

 

[evantful]

Instead of doing a plug read after idling, pull the same plugs after a long hard run and don't let the engine idle before you pull them.

That is a good idea to see if this is mostly an idle rich issue. I will try that when I get the boat in the water.

 

[Jason89sunbird]

I would defiantly check temp at the sensor using temp gun or multi-meter. if its a standard gm resistance value sensor look for roughly 170(212 degrees) to 300(180 degrees) ohms to ground. with both tests it tells you if the sensor and thermostat is good. the last step in the coolant sensor test would be checking ecu ground wire at the ecu to a good ground point on the engine, ie no paint, bare metal for a resistance/continuity good would be under 3 ohms best would be 0. my gauges to engine resistence is roughly 5 ohms. wiring in boats have a lot of things going against them, especially at connectors. Replacing the injectors at 650 hours wouldn't be an unwise maintenance item, all TBI research I have done indicates you cant trust injectors with high mileage to flow the proper amount, most of them flowed too much when trying to source them from the bone yard. That would give poor idle and alright WOT.

Good luck

I just look at the spark plug pics, if they are in order then #7 and 8 are the worst with 3 or 4 following. On a tbi motor knowing which bank is richer is important, 1,4,6.7 burn off one injector then 2,3,5,8 off the other.

 

[evantful]

Jason, thanks for the feedback. I am considering getting a Rinda Techmate and going through all the various sensors and making sure they are all in spec, even though they have been replaced, to help rule out wiring trouble.

In regards to the spark plugs to confirm what plugs I mean reference the photo below, rich Cylinders marked in red. Its Cylinders 3,7,8. Cylinder 7 seems to be the worst on both the new and old plugs, 8 is very close behind. Cylinder 3 isn't as bad as the other two but still much more than other 5.

It would seem the right bank of the engine is having more trouble. The plugs on the left bank with the exception of Cylinder 8 all look good.

 

[Jason89sunbird]

with 7 and 8 being the worst I would be doing a compression test. Warm up the engine and check all 8 cylinders with throttle wide open. You want the engine warm, an exhaust valve that doesnt seal well (burnt) shows better warm. 7&8 have nothing in common (different banks and intake system) except heat, the hottest part of the engine. If compression is way off its time pull the heads and check valves and cylinder wear. If its questionable or decent its time to do a leak down test. If its perfect I would then do a quick running compression test, actually I might do that while warming it up lol.

 

[bruceb58]

Jason, thanks for the feedback. I am considering getting a Rinda Techmate and going through all the various sensors and making sure they are all in spec, even though they have been replaced, to help rule out wiring trouble.

Out of curiosity, where are you located? I own a Rinda and maybe a few others on iBoats that live close to you own one and would be willing to share.

 

[evantful]

Hey Jason,
I had performed a compression test, plugs out, warmed up (on muffs), ignition disabled, throttle wide open. The cylinders were between 182psi and189psi. I am considering doing a leak down test, never have done one before but It seems worth while at this point. I have read about others in the car world with 305/350 SBC's where the #7 and #8 cylinders develop valve trouble well before the others, whether it be seals or something else.

Bruce,
Im based in Montgomery, New York (Hudson Valley). I would certainly be grateful if anyone would willing to let me borrow it for a few days, I wasn't sure how to go out asking or if that was against forum policy.

 

[Jason89sunbird]

I thought I replied already, tis forum acts up on my phone. I would definitely do a leak down test. I wouldn't convert it to Carburetor, that's silly. Exhaust valves get a lot of abuse, do you know how to do a leak down test? I have used the harbor freight one successfully.

 

[bruceb58]

I don't think you are buying much doing a leak down test. Your compression is great. Best thing a leak down test does is to pinpoint the cause of a cylinder with low compression.

 

[Jason89sunbird]

He isn't complaining about power, misfire or driveablity for that matter. He is being very particular which I don't blame him. I have had plenty of engines show good static compression test and had questionable running compression results, a leak down test then pin pointed the issue.

 

[ericga]

evantful,

The hose between the throttle body and the MAP is leak free and connections tight? Is there a chance you were given the wrong MAP sensor for your application 2 years ago (1,2,3 BAR)?

 

[bruceb58]

I have had plenty of engines show good static compression test and had questionable running compression results, a leak down test then pin pointed the issue.

You do understand that a cylinder leak down test is a static test right? A cylinder leak down test is usually never done after a good dynamic compression test. A cylinder leak down test pinpoints a compression issue to be either exhaust valve, intake valves or rings. If you do a dynamic compression test and get 180s, you already know those are all good.

 

[Jason89sunbird]

I understand, when you have an obvious problem that is true. We are talking about a slightly rich cylinder. I had a nissan with a rough idle when warm. It had the same compression cold and warm, about 160 on all 4. leak down test heard noise in tailpipe. I pulled the head, cut the 4 valves and put it back together. Smooth idle. There was no power issue, no misfire at idle, no driveability problems above idle. Just rough idle. 150-250 cranking rpms is slow enough for a slightly burnt valve to seal, the sharder valve in a compression gauge has such low resitance, compression would rather go to the gauge then out the exhaust. Here is a link about compression test. I'm not going to argue about how one wants to name each test. I just have real world experience and am a Master tech at a dealership. Don't be the reason people don't like to help others. He could keep shotgunning his boat.... http://www.misterfixit.com/dyncompr.htm