Volvo 5.7 GI-E Backfiring at 3100 RPM

echandler1971

Sorry for the rambling and sometimes repetitive nature of this. Typing this on an iPad really makes putting thoughts in words harder. 

So, we closed on our 05 350 FV and on her maiden voyage from the storage marina to her new home, we started to get backfiring on port engine at 3100. That was only after a terrible problem getting it started after she was dropped in.  My mechanic had done a tune up on the spot when the engine wouldn’t start, replaced fuel pressure regulator and tested fuel pump. He claimed that the port tank had bad gas and charged me $1100 for parts and labor and told me to have the 80 gallons pumped out. Still he got it started so we left it running and took off. As soon as we tried to get on plane, the backfiring started. 
The twin engine runs fine. Before a logistical nightmare of having a tank pumped, I tried an experiment - isolate both engines to the starboard tank. Experiment failed. Port engine still backfired.  See video below. How, if using the exact same gas, one engine backfires and one doesn’t?  It didn’t add up and I wasn’t spending more money on the mechanic. 

Here is what I did after that:
1. Emulcifier in port tank - could be water due to ethanol over winter storage - done before my experiment so kinda irrelevant 
2. New port fuel filter - was old full of water? High RPMs could splash over
3. New port ignition coils - theory that at high RPMs possibly it’s not providing enough amperage/voltage for a hot spark
4. New injectors- South Bay 8-pack. Could have a leaky injector or bad spray pattern or spray volume in a cylinder. Plan is to ship old ones out to get tested, cleaned and be ready to use in other engine as as set tested together. I used a YouTube video to replace them. Very helpful. 

Boat came with a brand new spare fuel pump, which I guess I could try next if my work fails to fix it.  Anyhow, engine was purring at the dock on a stormy yesterday. We’ve been battered the past few days. I got her up to 3100 no problems but no load. It’s the load that will really tell if it’s fixed. Memorial Day will be the big test as weather will be favorable. 
I sorta threw money at this because the Admiral had lost all patience with our expensive floating camper I purchased, but saved some money by doing the work myself.


https://m.youtube.com/watch?v=vOIiQTr6dzE&feature=youtu.be

aero3113

I don’t know much about Volvo’s but I’m thinking what you’re hearing is a bad fuel pump. @Aqua_Aura might have more information to add.

aero3113

It almost sounds like a cut plug wire arcing also.

Aqua_Aura

Well I definitely get how you feel as far as spending all that money then having issues. It sounds like you went through all the typical repairs to try and correct the issue, as I was reading every idea I had kept getting addressed. Honestly it may just come down to running it and getting it "cleared" out. I had these same issues but mine was just bad fuel however it did send me done a whole patth of just about every aspect of these engines and what issues you could have. 

If it still didn't run well after a few hours I would check fuel pressures with a gauge you can borrow from most auto stores. Low side is something like 15 psi and high side is maybe 30-40. You can Google it and you should be able to find it easy, I know I'm not accurate enough to use those numbers for testing. Paint chips in the fuel system can be an issue from the painted interior of the pumps but it sounds like you may have eliminated that. 

How many hours on these engines? 

Did you check the plug wires, you can do a resistance test on them?

Does this engine have a cap and rotor? That may be a point of failure. Can't remember if that year had electronic ignition. 

LaRea

+1 on spark plug wires.  

echandler1971

If I’m having the issue after today’s run, I’ll check the wires. The engines were rebuilt 2 years ago so they have 100 hours each, but ECMs show 790 hours since they can’t be reset and are original. I would assume a rebuild would replace a lot of those things. I don’t know if this has a distributor or not. That’s still a mystery. I’ve heard things about flat top vs other kinds and arcing. To make things worse, I’m not exactly what you would call and engine guy. I’m an electrician, but am handy and have patience and youtube. Sometimes that doesn’t work so well, but it did work in the fairly-complicated injector swap out. 

echandler1971

Note that this only happens at 3100 and above under load. No backfiring otherwise. 

Aqua_Aura

I think you do have a cap and rotor so I would definitely give that a check, very easy fix.

YYZRC

I had the same symptoms as you @echandler1971 on a previous boat with the Volvo 5.7 and it was a loose spark plug wire.  Agreed with @aero3113 and @LaRea, I would definitely look at wires first.

echandler1971

Well, I’ll do that next since it happened again. We did go for a while before it happened this time. We decided to go it slow to burn off this gas that could be bad. A friend from work took this shot of us today  

aero3113

Awesome pic @echandler1971 !!

andyd

Volvo-Penta fuel pumps of that era were painted on the inside. The paint comes off and causes problems, the least of which is a high pitched "whine." Not sure which YouTube video you watched, but I recommend contacting www.ManCaveMechanic.com and talking to Troy. He is the V-P fuel problem guru. As others have stated, make sure your ignition system is new and top-notch, plugs, wires, distributor cap. Also, any questionable fuel should be replaced with the fresh stuff. Good luck! Andy

Aqua_Aura

I believe Troy unavailable for a few weeks.

Unfortunately those paint chips will come off and go straight to the injectors however he did the injectors and issue remains so not sure that's the problem. 

echandler1971

ok, today I swapped the flat distributor cap (apparently these are notorious in VP engines) and new plug cables. Won’t be able to take her out till tomorrow. Revved her to 4,000 without issue, but seems to be under load that this happens. 

echandler1971

Took her out and finally got her up on plane (25 knots) and 4300 rpms! She worked great! Then I slowed down and the engine went back to its backfiring at 3100. When we got near where we were to anchor and swim, both engines died and I couldn’t  get them to start (flooded). We spent a few hours and after some throttle, I got them both started but backfiring issue remained. We puttered home at 3000. I’m finally at a point I can fill up the gas tanks. Hoping it’s bad fuel from last season. 

echandler1971

So, now I'm wondering if it's the MAP sensor. It seems the backfiring happens when the engine really heats up - I got her up to 25 knots after all and only after running her that way for a while did this backfiring happen. Possibly the MAP sensor is causing the engine to run rich or lean? Anywho, the $10k question is where the heII the sensor lives on my engine. The VP diagrams aren't very useful in this case.

echandler1971

Found the MAP sensor. Will replace next week. IN the meantime, the boat came with a spare fuel pump, so I swapped that in last night. Will test this weekend. Testing is harder because I have to parade route 1 mile to get to open water to test higher RPMs under load.

echandler1971

No compression test yet but new fuel pump now has me backfire at 4k RPMs instead of 3.1K. Seems like a supply issue.

awesomeame

You need to check your high and low fuel pressures under all engine conditions.  Low side should be 4-8 psi always, high side 50-60 psi always. (27-31 if you have a throttle body, but I think you’re mpi) if your numbers are outside of the ranges then there’s a problem.  If they’re in the range then your supply issue is ok, although you could still get your injectors flow checked/cleaned.  About 20$ea around here.  You could Buy the clymer/Haynes manual too it’s a wealth of info and has great fuel system troubleshooting guides.

matt

echandler1971

Well, I took the boat out and took pressure readings at idle and at the point of backfiring (now back to 3k RPM). It stays consistently at 50-60 psi. I replaced the MAP sensor to no avail. I'm starting to get frustrated and upset. I have an appointment possibly 3 weeks out with the mobile marine Volvo guy, but not against trying other things in the meantime. I still think possibly the TPS has issues, which would explain possibly bad mix happening at certain RPMs?

echandler1971

I believe I have fixed the issue and it was a somewhat obscure solution. The short answer was it’s was the ECT - Engine Coolant Temperature probe used by the ECM as one of several input devices to help it calculate fuel mix. It was reading way way wrong and the ECM was flooding the engine with fuel. 

Longer version: I had installed 2 FoxMarine engine gateways in April. When we got the backfiring happening, I took screenshots from the FM app of both engines. I wasn’t looking at the right place originally, focusing on the MAP and fuel rates and whatnot. The data was staring me in the face. It showed after driving 30 minutes that the coolant temp on the bad engine was 47 degrees F while starboard was showing 155. The ECM saw the port engine as really cold, needing more fuel. This was fine at low RPMs, but higher, the engine got too much gas and caused rich backfires (I assume).
Ran her today up to WOT and no backfires with new ECT. 

I’ll post a new thread about my remaining issue of stalling at low RPM after I search the site to see if it was answered already. This site is very useful and I hope my issue and the resolution will help others down the road. 

Lake_Bum

The symptoms you are describing sound VERY similar to my friend's boat on our last trip together.  He has a Volvo/Penta 350 mag.  He was getting the backfiring under a load.  It was a sensor.  He thought it was the fuel pump, and he had an old school fuel line with the squeeze ball to remedy what he thought was wrong.  After messing with it a little while, he determined it was a small sensor.  A temporary fix got him through the weekend.  I believe the plastic tabs were worn out, and he clamped it together. 

andyd

It's very useful to know about this, thanks for the update. Andy

rmfriday

It’s crazy but a very similar thing happened to me start on a return trip Sunday. My 2005 VP GI-E 5.7 port motor started backfiring. I also have the fox marine interface so I looked at it and all looked good so I ruled out the temp sender that solved the original posters issue.
so I start swapping parts from one motor to the other, coil, IAC valve, fuel pump assembly, cap and rotor, checked spark on each cylinder. Still back firing at higher RPMs, guy at the marina who is a decent mechanic thinks it valve train related and either a valve sticking or the cam is shot, he suggest to put a vacuum gauge on it to confirm it has a valve train issue. Once the vacuum gauge is installed and motor is running the vacuum is stone cold steady but a little low(14.5 in) at idle, he suggest rotating the distributor to try and increase the vacuum, I am reluctant because I set the base timing last year and can see the spark advance on the fox marine app. but I figure at this point what the heck. So I get the motor started and it is at idle, loosen the distributor and turn is a little each way, nothing, then I turn it till it’s stalls. This is kind of how I thought it would go but wasn’t sure so we rev it up to see what the vacuum gauge does at the ramp it was backfiring at, now it won’t backfire at all. I tightened down the distributor and tried it out two or three more times and still no backfire.I guess the distributor shaft has developed a slight amount of play and that is what caused it to be out of time and the slight adjustment we made solved the issue?
all and all I am happy to have it apparently fixed but and a little nervous for this weekend.
I put all the parts back on the starboard motor and it is also running correctly.
I am hoping it all stays this way...