Hesitation/bogging during hard acceleration Volvo Penta 5.0 GXi-A

[callen369]

Good afternoon all,
I'm hoping for a little direction. I have an '02 Chap 230ssi with a VP 5.0GXi-A hooked up to their DP-SM drive. Engine numbers - 4012050911; 3869116 and drive 4202037752; 3868913. This boat is new to me, June this year, and it is my first fuel injected boat. I noticed the hesitation when I water tested, but it had been sitting with old (6-12 month) fuel. 400 hours on motor, and other than fluid changes, not much maintenance done. I have done the following in an effort to bring the maintenance up to date, and get rid of the hesitation.

1. replaced cap & rotor - were moderately corroded, but no help
2. plugs and wires - appeared original, plugs showed normal wear - were gapped anywhere from 48 - 58, set mine to 60
3. fuel cell, disassemble, clean all screens, water ports, new filter - old filter had no water at all surprisingly
4. though batteries and connections looked pretty nice, cleaned reattached securely, and checked ground wires, harness connectors for corrosion and security
5. opened throttle body, pulled injectors, and was surprised to find them very clean, mild corrosion, but no ethanol related gunk, checked regulator, sprayed clean, not much there, cleaned pressure and return lines and re-connected
6. today I completed my inspection of the fuel system. pressure were 15 & 32 psi rock solid from idle to WOT under load, did notice that fuel pressure drops off immediately after key turned off during setup...don't quite recall if that is normal on this system - please chime in - even added a clear section of fuel line to check for air ingress prior to the filter, and no bubbles.

Now, correct me if I'm wrong, but with these fuel injected motors, there should be no hesitation or bogging. You can feel it in the boat, like it's not getting quite enough fuel. It's not that it runs bad. You can smoothly move the throttle forward and she accelerates fairly evenly, but if you drop the hammer, she sputters a bit and takes a couple seconds to come out of it.

Suggestions?

 

[Saline Marina]

If TBI (I think so) a possibility is the TBI gasket (to the intake manifold) also possible are bad readings from either or both of the MAP (maniifold absolute pressure) or TPS (throttle position) sensors. Both of those are used to lookup the injector pulsewidth from a table. The coil is also a possibility although I think you'd have the same affect at steady WOT as on an accel. Any other vacuum lines (if there are any) should be carefully checked for cracks or degredation.

 

[callen369]

It is a TBI system. Will have to give the TPS and Map some thought. I agree with the coil, would most likely have issues all the time if it was failing. And no vacuum line, thankfully, have enough trouble with those plastic tubes on my cars.

 

[callen369]

May have located the culprit....Ohmed out TPS, starts @ 2.10k at idle, slowly climbs to just over 3k at 3/4 or so, then drops back down to 2.7k much above. I'm no expert on TPS readings, but I'm pretty sure its basically a potentiometer, and the readings should have been linear up and down. Right??? Thanks for the direction Saline.

 

[Saline Marina]

I don't know with authority but I'd expect the exact same as you...a climbing resistance that's always increasing the more that the throttle is opened with max ohmic reading at full throttle. With the same reading at two very distinct places on the range of travel that would confuse the ECM as to what exactly the throttle position would be. Hope this is the issue. I think the MAP sensor can be tested with a hand-held vacuum pump, I have one from a long time ago for solo-bleeding brakes the old, hard way...

 

[callen369]

I was going to test the MAP as well, but it has crimp clamps on the fuel hose/vacuum line, and I didn't have any extra barbs to splice it. I'm fairly confident the TPS is shot. Weird that there is no part number for it listed in volvo penta store...guess it's a straight up GM TBI sensor. Least I'm not replacing a fuel cell at 700 bucks! Will pick one up today and lake test tomorrow. Thanks again.

 

[callen369]

Well, no luck. Guess I will have to check out the MAP sensor.

 

[callen369]

Pickup up a MAP sensor to try, and again no help. Also changed the coil as I am running out of ideas....no help.

Took it out today, advanced the timing via the distributor a bit, and it started better, as in before I had to crank a few seconds, this time a bump of the key. But, not really any better on plane or acceleration, so after a few minutes and a little pinging, returned it back. Same ole game. Retarded it slightly, and still about the same. It was up to temp before testing, as we have a decent size no wake zone. Wanted to check it with a timing light, but...the few marks on my engine are hard to see, and looked to be alright for base, but there are not enough for total timing. Will have to get a sticker or make my own marks.

Thoughts on a pickup coil? or other ignition/timing related problems? I am borrowing a compression tester just in case, but won't be able to get to that until later this week.

 

[Saline Marina]

Squirrelly problem. There are some aftermarket TBI fuel pressure regulators available where you can tweak the fuel pressure to the injectors and thus the flow via an adjustment mechanism in the regulator spring. If you google something like GM TBI fuel pressure regulator there are some sites which come up. The claims are you get a possible range of several psi with the stock spring due to build variation. Not really sure if the adjustable spring kit meets any of the marine fuel requirements but might be useful for making a short-term change and seeing if there is any help. I think there are services which can clean the fuel injectors, wondering if they can also check cumulative flow over several minutes' time to assess the condition.

The only other thought was going to be about the thermostat and/or coolant temp sensor. TBI is a wet manifold (wet with fuel flowing thru it) and so if the engine is running cold, there can be issues with the vapor condensing into liquid. My TBI truck stumbles and coughs when its cold, for a little bit until the intake warms up and even the TBI has internal waterflow heating to help with vaporization. When warm it runs like a champ. Not sure if the coolant temp sensor is used in the boat motor but it would also have some affect on the fueling, as would the thermostat, if stuck open, could have just enough affect on the fueling to cause a minor problem. These wouldn't be the first things to check but since you've eliminated the other ones its down to "other possibilities".

 

[Tail_Gunner]

Squirrelly problem. There are some aftermarket TBI fuel pressure regulators available where you can tweak the fuel pressure to the injectors and thus the flow via an adjustment mechanism in the regulator spring. If you google something like GM TBI fuel pressure regulator there are some sites which come up. The claims are you get a possible range of several psi with the stock spring due to build variation. Not really sure if the adjustable spring kit meets any of the marine fuel requirements but might be useful for making a short-term change and seeing if there is any help. I think there are services which can clean the fuel injectors, wondering if they can also check cumulative flow over several minutes' time to assess the condition.

The only other thought was going to be about the thermostat and/or coolant temp sensor. TBI is a wet manifold (wet with fuel flowing thru it) and so if the engine is running cold, there can be issues with the vapor condensing into liquid. My TBI truck stumbles and coughs when its cold, for a little bit until the intake warms up and even the TBI has internal waterflow heating to help with vaporization. When warm it runs like a champ. Not sure if the coolant temp sensor is used in the boat motor but it would also have some affect on the fueling, as would the thermostat, if stuck open, could have just enough affect on the fueling to cause a minor problem. These wouldn't be the first things to check but since you've eliminated the other ones its down to "other possibilities".

The temp issue is quite real, recently i had a thermostat stick open and the engine would run at about 170 under low rpm but as soon as i started to go to wot or mid wot you could watch the gauge pull down to 100 degree's...a bit strange ive never seen that before on any engine. Needless to say she also bogged going from 2800 to wot...just a momentary bog and then clear herself up. Pulled the Thermostat replaced it and steady temps once again and the bog is gone...I do know that MEFI does have a low temp enrichment circut for low temp's but i dont know if that is effective at high wot....If it was fuel starvation i doubt it would clean itself and smooth out at high rpm....if anything it should pop..aka backfire.... higher rev's less gas and then it right's itself?????


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[callen369]

Have my Ignition Control Module and pickup coil to try out today. And may run the compression test as well. My coolant temp climbs to about 160/170 and stays put. I do have an extra thermostat on hand, so I may change it as well. Preventative maintenance. Wish I had the adapter to set base timing, will have to hardwire it myself to check it.

Can someone verify the correct plug gap as well?

Did look at the adjustable fuel pressure regulator....have to drill a hole in the throttle body in order for that to work, but will keep it in mind.

If I ease the throttle all the way up, it runs fine...push too much for takeoff or to accelerate, and it stumbles and starts to clear after a couple seconds.

 

[Saline Marina]

As far as I know, the low coolant temp/warmup strategy for TBI automotive (truck) apps works along these lines. The initial coolant temp at the time of startup chooses (from a lookup table) an injector pulsewidth to simulate the "choke" function, i.e. overfuel for a reliable start event. After that its more or less a gradual ramp down in the overfueling to get to normal running fueling. Basically its a timer developed from warmup curves on the engine based on ambients and not a continuous modification.

Not sure if I'm explaining it clearly but the warmup fueling is basically a timed event that ends. A new start event drives a new warmup event (no matter if thats a hot start or cold start or somewhere in between), but once the warmup timer is expired, there is no more fueling compensation for coolant temp. Its just assumed that the engine is warmed up and the temp controlled by the thermostat (or radiator fan thermoclutch if towing in a truck). I can't say for sure what the marine strategy is, but my guess is it mirrors the automotive strategy fairly closely wherever possible to avoid additional engineering development expense that GM Powertrain has already done.

Newer engines with more sophisticated diagnostics do a lot more testing and examining of sensor data to see whats happening for diagnostic purposes. But TBI is a pretty basic and simple system. For related interest, the engine is validated to start reliably down to -40F overnight low limit with no assistance if the battery is in good enough condition. To start at lower ambients than that, a block heater or other external heating is required.

 

[callen369]

Well, we have another problem. I took it out briefly after replacing the pickup and module, and it ran rough the whole time. So I anchored, pulled the plugs for a look, and #6 is missing it's electrode, along with about a 1/4 inch of the ceramic. So now I will have to vacuum it out, compression check it, and stick a scope in it if I can find one to borrow. Fingers crossed....So for now, not sure if I ever fixed the original problem with any of the sensors, as they were replaced after the plugs and wires.

 

[callen369]

They say a picture is worth a thousand words...I seem to be using a choice few....
Will have to dig into it a little more tomorrow, as the valves look fine, and aside from 2 really small scratches/marks on the head, the piston appears ok. Will have to see if the piston will move tomorrow and what kind of shape the walls are in. Pull those valves and make sure the seats are ok, and that there aren't any cracks....If that all checks out....does that mean I just had a blown gasket? Any other items I should look at as well?

 

[callen369]

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[callen369]

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[callen369]

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[Saline Marina]

Woh! I would not have pulled the head for that....hindsight is 20-20 but even at a 600 rpm idle the crank is rolling over at 10x per second with violent flows out the exhaust port when the exhaust valve opens there's a big "blowdown" to the exhaust port as the combustion pressure is released to basically atmospheric, and repetitions of that are piling up into the thousands. That missing piece is long gone. I think I would have "scoped" the piston (meaning bore-scoped) if possible to make sure the part didn't get embedded in the piston crown and it still looked clean, in order to build confidence. But at least you can sleep at night now.

I have seen a piston from a Formula 440 engine (2cyl IIRC) which had some kind of high speed detonation and several parts of the top ring land broke off the piston, brinnelled (think imprinted) the head and the piston like crazy and all the metal pieces were all gone out the exhaust port never to be seen again, at the time of teardown.

 

[callen369]

I was gonna scope it, but would have had to make a trip to work to borrow one. However, I compression checked it and had nothing.....so off with it's head! Found the head gasket between 4 and 6 looks like it was blown, probably been that way and was causing my hesitation issues the whole time. While valves looked ok, I wanted to check seats as well since I had it out, and noticed the intake valve looks a bit like a tulip. So I dropped it at a local guy to have the valve replaced and seated. Right now I am looking at ordering a set of risers and manifolds.... big chunk of riser fell off when pulled out of the boot. And a gasket set as well.

I had 10psi or less on the #6, and @115 I think on the 8, but those are the only cylinders I checked.....should have checked #4 as well, and probably would have seen the head gasket problem....

Just hoping I am lucky and the piston rod and all are ok. Cranked it over a couple times, and the cylinder walls look perfect and the piston still moves, so there is that. Fingers crossed.

Everyone local is way high on the riser kits, so it will be next week I guess before it goes together. Should have the head back today.

Any suggestions on brand of gaskets?

 

[Saline Marina]

Good find, then!

I have always been partial to the Fel-Pro gaskets, especially the "cover" gaskets with the blue material...I forget what those are called right now. Perma Dry maybe?

Also I'm a big fan of the Comp Cams chromemoly roller pivot-roller tip rocker arms (if you have the old stamped arm w steel ball joint. Just the stock ratio. The roller pivot takes a lot of load out of the valvetrain resulting in what I think is a longer wear life for all the components in the valvetrain. I've put them in both of my truck engines (a 4.3 and a 454) and had no issues for probably 120k miles cumulative.

The bottom end of GM's cast iron V engines, crank, rod and piston are very tough in my opinion.