MC 5.7 Vortech TBI Misfiring Need Help

[marinetech77]

I have a TBI 5.7 driving me nuts. I'll try and list symptoms and the troubleshooting I've preformed so far.Hopefully we can get to the bottom of this. Boat has a fresh longblock (I did not install) with the 1997 TBI components,and accessories changed over. Boat was sitting for approx 3 years or so,and has been operated in salt most of it's life. I have been running the boat for last month with no problems. Last weekend Racor finally plugged up after running about 100 gals of fresh fuel thru boat and coincidentally the engine is now running like crap. starts and idles fine put a load on it and at about 3k she starts to pop and misfire eventually stalling. I don't believe the problem is fuel.

Since last weekend I have cleaned fuel tank, fresh Racor, checked all fuel lines,removed fuel cooler cleaned inspected and reassembled, installed new injectors sonic cleaned throttle body, observed 35 psi of fuel pressure with absolutely no pressure drop during misfiring.Ran engine on outboard tank and it did not help. This leads me to believe the problem lies in the ignition system. I had a new coil so installed it, boat had new plugs wires cap and rotor installed 3 weeks ago, checked all grounds, checked harness and sensor plugs while engine was running flexing tugging etc. at 2k and no change. When cold the engine fires up perfectly, the misfiring happens under load, and also at no load high rpm in neutral. I can dump throttle in neutral a few times and engine acts like it cannot find the correct advance.
I proceeded to check timing by locking base timing w/ scan tool and I cannot lock base timing with the tool. It will not allow me to. I set the timing on 2 454 MPI's last week with no problem (scan tool is working correctly). If I put my timing light on damper the timing mark is jumping around like crazy maybe an inch or more either way. Disconnect the timing plug on manifold no difference just different advance.
It's really driving me nuts as I have 2 days in this and I'm no farther than I was when I started. I hear that the ECM's rarely go bad. Could it possibly be a bad pickup in the coil? Maybe a knock module?Would it make a difference if the old motor was not a Vortech. the new motor is a 300hp roller Vortech. I'm not very familiar with this ignition system.I have factory manual #24. To top it off today I noticed the steering pin seal in the transom assembly is leaking (Bravo 3). Not really a big deal, just time consuming more than anything..complete engine, transom assembly r&r. Any help would be greatly appreciated. Don if your reading this I've read many of your posts, and your troubleshooting knowledge is needed. I steer more towards Cat,Cummins,Man,Detroit myself. Boat with problems is my 24CC Silverhawk. I will post replies as this thread carries on until a cure is found, so hopefully someone else will benefit.

 

[boat127]

Re: MC 5.7 Vortech TBI Misfiring Need Help

i read your post and have some ideas. i would check the valve adjustments and also make sure your arn't getting water injecting into cylinders bad riser gaskets.

that is weird you can't get the scan to set it into base timing.

also could be a vaccum leak at the intake manifold

 

[ENSIGN]

Re: MC 5.7 Vortech TBI Misfiring Need Help

Check for any water on the plugs...

 

[John_S]

Re: MC 5.7 Vortech TBI Misfiring Need Help

Have you hooked up a vacuum gauge or did a compression test? My guess is when the racor was near plugged, you were running lean and might have tuliped a valve or caused other internal damage.

While I don't understand what is going on with your ECM, I'm not a believer in two independant things going wrong at the same time. Possible, yes, likly, I'd say no.

 

[marinetech77]

Re: MC 5.7 Vortech TBI Misfiring Need Help

I just installed new risers and manifolds so I don't think water intrusion is an issue. This motor only has about 50-75 hours on it. The problem is that it was installed like 5 years ago and the boat has not been used. Evidentally the previous owner had issues with getting the timing set as well. I come to find out they power timed it and as we all know you can't do that with these ignition systems. About 3 years ago the for some reason the motor was pulled and the heads were pulled and valves re-done, evidentally compression was inconsistent not low. Valves werent't seating properly because of corrosion. Although I'm not ruling out valve train wouldn't a bad valve give poor performance thoughout the rpm range? I will do a compression test and see what we have. I'm also not a big believer in 2 different problems unrelated occuring at the same time.Thanks for teh help I'll keep you posted

 

[Don S]

Re: MC 5.7 Vortech TBI Misfiring Need Help

If you plugged up a Racor, you may have also put contaminated fuel into the injectors. Pull the top off the VST and check. Should be nothing but clean fuel in the bowl. If it's dirty or has water in it, you can bet it's in the injectors too. Might want to send them out and get them cleaned and checked.
After you do get the problem cured, you need to start changing that fuel filter yearly and checking the contents of the old filter in order to head off future problems.
For your 97 or earlier engine, you should be using manual #17, not #24.

 

[John_S]

Re: MC 5.7 Vortech TBI Misfiring Need Help

These statements: "I have been running the boat for last month with no problems." and "Evidentally the previous owner had issues with getting the timing set as well. I come to find out they power timed it" seem to be conflicting. Am I correct in assuming that the timing problem was there over the last month, but you did not notice any problems. Your current missfire only started after your fuel system plugged up?

I'm not a fuel injection guy on cars, let alone boats, but I believe that the fuel map is different between a standard head TBI and vortec TBI. 2ndly, we don't know how close your vortec long-block is to a standard Merc vortec. They must have put a different intake on, at a minimum. Compression ratio and cam would be the other areas that could cause differences in required mapping. There is certainly the possibility that you were running borderline lean at some rpm. With the additional fuel restriction, could have put it over the edge.

 

[marinetech77]

Re: MC 5.7 Vortech TBI Misfiring Need Help

Okay sorry for the conflicting statement. I purchased the boat a month ago from a customer of our marina. The owner of the marina who has also been working on boats for 30+ years told me it was a good deal and showed me some previous invoices on the boat with nothing major to speak of.I bought it and have been running it for a month w/ no problems at all. All of a sudden I start to lose power and then a very large misfire occurs the boat runs like crap for about 10 more mins finally cuts out and can not restart. Racor ended up being clogged so a fresh filter and outboard tank was brought out and I ran back about 3 miles w/ no problems.Cleaned entire fuel system and now the start of misfiring as described. I come to find out that a few years back there was a base timing issue that was never really resolved, so the motor was power timed and there it sat rarely used until I bought it and ran for this past month.Although I have not personally verified, but I'm told by my boss that the motor installed is a marine base 300hp Vortech roller motor. I have not done a compression check yet to rule out valve train.
I'm still perplexed as to why the timing cannot be locked by the Mercruiser scan tool. Is there another way to lock base timing as in possibly grounding a pin in the DLC?As I said before the timing mark is jumping around like a Mexican jumping bean.The fuel system has been ruled out at this point. The plugs are black so it was running a little rich. Would a bad TPS cause the symptons I've stated?I will be doing comp test tomorrow.
Don the motor in question is a 350TBI Bravo3 setup.I'm sure you answer a ton of questions so you probably have me mixed up with someone else. As far as the VST tanks on the Opti's and HPDI's I been cleaning quite a few of them.
Any ignition troubleshooting secrets would be helpful for my boat. I heard a guy tell me to get a propane plumbers torch and when the engine starts running bad give a small shot in the flame arrestor if the motor picks up and runs better you instantly know it's a fuel problem if no change is heard you know it's an ignition problem???I get the thought process but sounds like a good way to blow it up???

 

[TilliamWe]

Re: MC 5.7 Vortech TBI Misfiring Need Help

This is from a Volvo manual, but it might help, since they are done the same:

The Mercruiser manual should have this procedure in it as well.

 

[TilliamWe]

Re: MC 5.7 Vortech TBI Misfiring Need Help

Don't be surprised if you have really low compression on a few cylinders (tulipped valves). Vortecs do NOT like to be run lean or have high combustion chamber temps. And no, they don't necessarily run terribly at all rpms. The problem first become noticeable at about 4000rpm under load. Then it becomes more and more obvious throughout the RPM range the longer you let it go. But I have a cylinder with ZERO compression, and my 97 5.7LX EFI Gen + would still turn 4800rpms WOT, and didn't idle rough at all.

 

[marinetech77]

Re: MC 5.7 Vortech TBI Misfiring Need Help

When I check tomorrow what difference should I be looking for. I would hope to see numbers at or near the 170 range. At what point would you consider pulling the heads 30 psi difference? Thanks for the schematic.

 

[marinetech77]

Re: MC 5.7 Vortech TBI Misfiring Need Help

Was able to set timing correctly today. Without the scan tool after starting engine, terminals A&B on the DLC connector have to be jumped. Compression test was good with all cylinders 180-190 psi. On one of the cylinders it stuck me odd when I pulled the spark plug (cyl6) it made a sound like there was pressure in the cylinder or vacum don't know which but I duplicated the sound using the comp tester. Checked comp, relieved pressure from guage removed plug adapter and hissing sound occured.I noticed a considerable and I mean considerable difference in temp on the starboard riser. Both risers and manifolds are new.Port riser ice cold at all throttle ranges starboard went from cool to can't touch hot upon throttle increase. Don't have exact temps as I lent my laser out. I guess next will be a leak down test. Possible combustion gas leak into cooling system?? Throwing knock and coolant temp sensor off, causing erratic signal to ecm. I know my symptoms sound odd and conflicting but I am just reporting whats happening. Between myself my boss and my father there is almost 100 years of combined exp in the boat and auto repair business. We are scratching our heads so to speak! It's ridiculous actually.

 

[vxtech]

Re: MC 5.7 Vortech TBI Misfiring Need Help

check headgasket for leaks, possible burnt fire ring on gasket from running lean, or heads may have needed retorquing on rebuilt engine after warm up

 

[lonemust]

Re: MC 5.7 Vortech TBI Misfiring Need Help

Not sure with boats but on cars when this happens sometimes it's the cam positin senser on the front of the engine. IF marine engines use it it can cause all sorts of timing problems since it tell the ecm what the cam position is. Like I said though I don't know if marine engines use that senser. If so it should be on the front of engine by or in the timing cover.

 

[lonemust]

Re: MC 5.7 Vortech TBI Misfiring Need Help

Just looked at the manual, apparently marine eng's don't use the cps. So it wouldn't be that. But it could be the MAP senser it can too cause wierd things to happen, usually at idle or just off idle. But can do it at mid-full throttle also. And matine eng's use a MAP senser. Something as simple as a leaky or broken hose to the MAP will wreak havoc on the ecm 'cause it won't read properly from the MAP. So check the electrical plug and vaccum hose on the MAP senser. Most people don't even think of things like that unless they have a scan tool for the computer and it shows up on it.

 

[marinetech77]

Re: MC 5.7 Vortech TBI Misfiring Need Help

This model is a TBI not a multiport, I don't believe it has a Map sensor (1997) . We have located a fuel line under the motor, the supply line from can filter that has a kink apparantly from the motor being installed and removed a few times. Mercruiser is sending me a new one, so we'll see what happens after I in stall it. Has been too hot lately to work on it outside in the sun and the shop is full.

 

[marinetech77]

Re: MC 5.7 Vortech TBI Misfiring Need Help

Problem Solved..I think...After changing the kinked fuel line, and swapping out the TPS, pickup, etc. there was no difference. Alas the slightly corroded fused link in the guage harness. I was able to keep the motor running at 2k long enough to discover a fused link that was taped up and bundled with a few other wires stuffed behind my fresh water tank. Link was part of the ignition circuit, that energizes the ECM w/ 12 volts. As I started squeezing the bundle she cut out like a light. The corrosion was hampering a constant 12 volts to the ECM, which would make sense why my scan tool kept telling me unable to communicate w/ ECM, and would also explain my flickering digital guage problem. A new link was installed and she ran for over an 1/2 hour on the muffs under different RPM's w/ no stalling and a smooth idle.I'm sure the fuel system had some part in the poor running as there was a ton of crap in the injector cups. Will be checking all connections and putting di-electric grease in all plugs.