Volvo Penta 1999 5.0 giwptr -Running Lean on 4 cylinders

jimc46

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I hope some one can help!!! Have developed a rough idle and some roughness at open throttle ( small vibration) on my Sig 240. Also have found that I am getting a lean fire on plugs 1,5,6,and 7.Here is what I have had done so far.



1. Had tune up done (new plugs, rotor ,distributor cap.) Checked timing.

2. Replaced Fuel filter and checked fuel for bad fuel .

3. Checked fuel pump pressure (ok)

4. Replace Throttle body mounting plate and TB gasket.

5. checked cylinder compression. ( all cylinders at 173 or above compression)

6. Sprayed ether on intake , throttle body, no leaks

7. Checked for codes (no failure codes)

8. Replaced all plugs and ran engine. (same cylinders running lean)

9. Checked spark at plugs with light tester all plugs getting good spark

10 Checked crankshaft sensor (ok)

11.Checked MAP sensor (ok)

12 Cleaned IAC

13 Fuel injectors throwing nice cone shape and functioning properly

All of the above has been done by certified mechanic. They are at a loss as to what is causing this. Hoping someone might have an idea of what might be causing this.



Sorry for the long post !!!!!
 

Saline Marina

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The PCV could be an item to look at. Not that the valve is bad but if a hose is cut, etc. The PCV is a "leak" around the throttle blade which is metered by the little spring-valve and so if the low pressure (vacuum side) hose is compromised, its unmetered air entering the engine. The throttle body gasket and any vacuum lines which emanate from the TBI unit are the cause of most similar problems in a vehicle because they cause the exact same condition, unmetered air (which means its not compensated by an appropriate volume of fuel) into the engine.


Hopefully the fuel pressure was checked using the Schraeder-style valve. Is the "lean condition" diagnosis a result of visually looking at the spark plugs?
 
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alldodge

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I hope some one can help!!! Have developed a rough idle and some roughness at open throttle ( small vibration) on my Sig 240. Also have found that I am getting a lean fire on plugs 1,5,6,and 7.Here is what I have had done so far.



1. Had tune up done (new plugs, rotor ,distributor cap.) Checked timing.

2. Replaced Fuel filter and checked fuel for bad fuel .

3. Checked fuel pump pressure (ok)

4. Replace Throttle body mounting plate and TB gasket.

5. checked cylinder compression. ( all cylinders at 173 or above compression)

6. Sprayed ether on intake , throttle body, no leaks

7. Checked for codes (no failure codes)

8. Replaced all plugs and ran engine. (same cylinders running lean)

9. Checked spark at plugs with light tester all plugs getting good spark

10 Checked crankshaft sensor (ok)

11.Checked MAP sensor (ok)

12 Cleaned IAC

13 Fuel injectors throwing nice cone shape and functioning properly

All of the above has been done by certified mechanic. They are at a loss as to what is causing this. Hoping someone might have an idea of what might be causing this.



Sorry for the long post !!!!!

Figure it has to be the injectors. A good mechanic can test to see if the spray has a good cone shape but they need another machine to determine if they are operating correctly. There is a balance test which can be done to determine if the injectors are leaking. The best method is to send the injectors off to be cleaned and tested. Google fuel injector cleaning service and you will come up with several to choose from. Cost is around 20 each plus shipping
 

jimc46

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Saline yes we pulled all plugs and two looked like they were white and two looked grey. Replaced all plugs ran it for a while at the dock and pulled all plugs and got the same result. Also tested plugs with a light tester, showed all plugs firing and strong signal but ended with the same results. AllDodge thank you I am having a guy come out that works on injectors and throttle body next week THANK YOUU BOTH FOR YOUR HELP !!!!!
 

bruceb58

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Running at the dock is not what you want to do. You need to run with a load on it, stop the engine, and then do a plug read.

Can you run the boat over 2500 RPM under load? actually not sure if they use the SLOW on TBI models.

So does your mechanic have a scan tool that is showing IAC values as well as others? How did he check that the IAC is functioning properly? Did he turn off engine, unplug IAC and notice an RPM difference?

What was your fuel pressure? Is you alternator outputting proper voltage? Low voltage can cause your fuel pressure to be too low.

Did he check the vapor separator?

You have a factory manual?
 
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Saline Marina

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Agree that a bad electrical connection can cause trouble. When I first got my TBI pickup truck (7.4L) it would not idle for anything and I had to drive or stall. Eventually I found that there was a wire for the engine coolant temp sensor that the former owner or mechanic had butt spliced, but left about 3/8" bare wire sticking out of each end (!!!!) I cleaned that issue up while thinking of things I could try and it has run like a top ever since. The ECM voltage was being pulled down but not enough to have a hard short that would blow a fuse. In my case I had SES codes that led me in the right direction.

I think something on your nice list of checks which appears to be "in spec" is not. I can't recall if the TBI unit has a pressure regulator in it but that would be one thing to check out. Changing the TBI injectors is pretty easy, just don't drop parts down the throat of the engine. I imagine the marine versions are a lot more than the auto ones as usual.

I would also check out your spark plug wires. Despite the visual cues on spark plugs, its easy for a plug wire to get rubbed thru especially if its wire loom clips are missing or weren't followed rigorously. It doesn't take much of a surface groove to start leaking high voltage to ground and then causing cylinders which don't fire strongly that can cause the rough running. Its a cheap easy check, run your hands over them (w engine off!) to check for wear. My free advice if the loom clips are missing is to find replacements or else use black split conduit as those are really good in a chafing situation.
 
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dypcdiver

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A quick and cheap way to test the injectors would be to swap their positions and see if the lean plugs change positions too.
 

jimc46

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re checked fuel pressure and it is on the low side at 33 spec low side is 34 could this be the problem
 

bruceb58

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re checked fuel pressure and it is on the low side at 33 spec low side is 34 could this be the problem

Where did you get that number?

Should be more than 27 from the OEM manual. You have the OEM manual?
pressure gets reduced to 30 at the injectors by the fuel pressure regulator. You measuring the pressure under load?

Go here if you don't:
http://boatinfo.no/lib/volvo/manuals/wt_efi.html

Page 259 is the start of the TBI diagnostics.
 
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jimc46

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The 34 number came from the mechanic and he said I was on the low side. Pressure was measured from the Schraeder valve that is on the high pressure fuel line going to the TBI. It was at the dock running at idle. Bruce58 yes the boat will run at 4500 RPM the only thing I can feel at WOT is the engine running lean or misfire. At idle the engine is shaking at misfire.
I will be honest with all you great people at this point I am getting very confused and will be the first to tell you that I am not the worlds best mechanic but this is the second mechanic that just shakes his head and say I cannot figure it out.1000 ducks later and I am running out of ammo.
My gut feeling says somehow not enough fuel is getting to the cylinders. So here is a dumb question. I would like to do a vacuum test on the intake manifold. Shop manual says to hook gauge to a good intake manifold source. Can anyone tell me where this source would be . The only thing I can find is a TBI nipple that is on the front of the TBi covered by a sleeve with a cable tie holding it on.
Again I would like to thank everyone who has taken time to try and help. It is appreciated very much
 

Saline Marina

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I really feel like you need to look into the ignition system. One of those "spark plug visualization" tools which is basically a fixture with a threaded rod that is connected to a plug wire, the other end grounded. You open up a spark plug gap, then crank the engine to see what is going on. A HEI Delco ignition when healthy will jump a 1/2" gap in the tool on the end of a plug wire in free air (yes don't hold the tool while doing this its a bad idea, watch out for fuel vapors too, please). Its pretty amazing to see the fireworks given how small the actual spark plug gap is, I've done it on my TBI truck on all 8 cylinders. The difference is under 400psi of compression stroke pressure its a lot more challenging to create a spark and so the gap has to be smaller. Poor ignition comes very close to simulating a lean condition if you ask me as it has the net effect of no power, no feeling of power.

If you like to change parts like I do, I'd go after the coil, cap, rotors, plugs and wires and possibly the ignition module, look at the reluctor ring under the distributor base as that's the crank sensing in a TBI engine. Even if you scavenge some automotive stuff for troubleshooting purposes it would be OK, you could always acquire the proper marine parts for long term. The shotgun approach (change lots of parts at once) has a good chance of resolving this quickly and soundly. However it costs some more up front, but you can always fall back on the un-needed parts as future spares if you think like a maintenance guy.

This is where a vehicle has an advantage as there's an oxygen sensor (feedback sensor) to give you some clues about whether the engine is running rich or lean or ? They don't do well in the wet boat exhaust system, the boat engine fueling is just open loop but biased to the direction of slightly rich running.

The throttle position and MAP sensors also deserve a swap as these are critical to the proper injector pulsewidth.
 
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bruceb58

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If it is an ignition issue and it was a spark plug issue, he could take one off at a time and make sure idle gets worse.
 

Saline Marina

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Agreed just be careful, an old magneto ignition will hit you with a burst of energy. I've never confronted a HEI but something tells me its a lot stronger. I would be really careful of not handling plug wires etc with the engine running.
 

jimc46

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thanks for the replies. Workshop manual says never to unhook plug wires while running as it will probably blowout the coil. Salina have replaced distributor cap, rotor and plugs and will check the wires again. Used light meter on them and all showed good spark at the plugs. Again does anyone know how to check intake manifold for vacuum leak. I do not think this can be done with a gauge but the manual says to find a good source what ever that means
 

bruceb58

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Workshop manual says never to unhook plug wires while running as it will probably blowout the coil.
I guess that is a possibility. Out of curiosity, where in the OEM manual does it say this?
 

Saline Marina

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I have run from Detroit to Atlanta on a 454 truck engine with what I found later to be a plug wire hanging off the engine. I did have to change the coil about 3 years later as it did fail but I attributed that more to the ~22 year old coil than damage from the plug wire. Don't unhook *all* the wires at once but you can unhook one in my opinion to visualize spark.

Personally I'd try for a junkyard Delco coil off a truck for experimentation purposes. If it doesn't work I wouldn't think you are out very much change. If it does work buy a marine version and continue life. Sometimes you unearth a bad or poor connection in the process of changing a component you thought to be just fine and that's really the problem.
 
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