Mercruiser 7.4 MPI loss of power/stalling/will not restart

[timschap]

I have a problem on a 2000 Chaparral Signature 27 with a single Mercrusier 7.4 MPI (with a bravo 3). This is a new boat for me this year but I obtained the maintenance records for the last two years. The issue has been going on for at least two years and 60 hours of run time. The symptoms are: loss of power, cannot throttle beyond 2500 RPMs, stalling, stalling and NOT restarting (had to be towed in 3 times), backfiring, hesitation and skipping. It?s had three mechanics (one a ?Mercruiser certified mechanic) work on it. The problem goes away for a few hours of run time (3-15 hrs) but ultimately comes back. The part swaps have been: IAC - MAP /R&R, Fuel Pump Cooler Kit, Fuel Pressure Regulator, Fuel Pressure regulator (again)/Fuel Rail rebuilt (fuel pressure 38 PSI), distributor Module/coil, Knock Sensor, remove/clean/replaced, Cap/Rotor, Fuel Pump Kit (pump/cooler), PVC, Oil sending unit, and Temp sending unit. Currently the fuel pressure bounces between 25 to 33 PSI. I?ve contacted Mercrusier and was told to ?Take it to a certified Mercruiser Mechanic? ? big help! Does anyone have any other idea?s other than to take the engine out and swap it for an engine with a carburetor?

PS: sorry if this is in another post. If it is I could not find it.

 

[alldodge]

I have a problem on a 2000 Chaparral Signature 27 with a single Mercrusier 7.4 MPI (with a bravo 3). This is a new boat for me this year but I obtained the maintenance records for the last two years. The issue has been going on for at least two years and 60 hours of run time. The symptoms are: loss of power, cannot throttle beyond 2500 RPMs, stalling, stalling and NOT restarting (had to be towed in 3 times), backfiring, hesitation and skipping. It?s had three mechanics (one a ?Mercruiser certified mechanic) work on it. The problem goes away for a few hours of run time (3-15 hrs) but ultimately comes back. The part swaps have been: IAC - MAP /R&R, Fuel Pump Cooler Kit, Fuel Pressure Regulator, Fuel Pressure regulator (again)/Fuel Rail rebuilt (fuel pressure 38 PSI), distributor Module/coil, Knock Sensor, remove/clean/replaced, Cap/Rotor, Fuel Pump Kit (pump/cooler), PVC, Oil sending unit, and Temp sending unit. Currently the fuel pressure bounces between 25 to 33 PSI. I?ve contacted Mercrusier and was told to ?Take it to a certified Mercruiser Mechanic? ? big help! Does anyone have any other idea?s other than to take the engine out and swap it for an engine with a carburetor?

PS: sorry if this is in another post. If it is I could not find it.

Howdy

Fuel pressure bounce between 25 to 33 psi, could be injector, fuel pump, regulator and maybe electrical.

I'm guessing this goes on but there are no codes?

With this kind of issue wonder if there is a bad ground or bad ECM

What's your engine serial number?

 

[alamantia]

Do you have the old or new style ignition pickup in your distributor?

 

[timschap]

Hi, there are no codes. What is an ECM? I thought about bad ground but where? Not sure how to tell the difference between new/old ignition pick up. The serial number is 0L655708., Injectors have been cleaned, and fuel pump replaced.

 

[alldodge]

The ECM is the Engine Control Module or your engine computer. With you fuel pressure jumping between 25 to 33 psi is not high enough for the engine to run correctly, should be 34 to 38. Low fuel pressure will cause the engine to backfire do to running lean, will create a knock which causes the engine to reduce power (not going above 2500 rpm).

If power reduction is being caused by the knock sensor, the wire can be removed from it and it would come back. That said, by removing the wire it would set a code 44 in the ECM.

The non-start issue in most cases is fuel pressure. You would go into power reduction mode and non-start at the same time.

When the engine doesn't start do you hear the fuel pump turn on when the key to turned to ON?

 

[timschap]

Thanks, yes when the engine would not start we could hear the fuel pump working (with the ignition switched on). But he cracked the fuel filter and I turned on the ignition switch and no fuel came out (not sure if this is an accurate test of whether the fuel pump being bad but that was what the mechanic use this as justification for replacing the fuel pump/cooler). Should I have the mechanic replace the knock sensor? With regards to the ECM ... how do you know if that is bad?

 

[alldodge]

Opening the filter just allows air to be sucked into the pump. To check if you have fuel, you would push in on the center of the shrader valve that is on your fuel rail.

Should I have the mechanic replace the knock sensor?

No, not yet. If the knock sensor did not work or was unable to communicate with the ECM, there would be one of two codes. My comment was if you were unable to get above 2500 rpm you should be able to remove the wire and the engine would pick up speed. If it did pick up after removing the wire, slow back down, reinstall the wire and go replace the sensor.

With regards to the ECM ... how do you know if that is bad?

Your first post gave a lot of info and I was thinking you had some quality mechanics testing, but after hearing one check your fuel pump by loosening the filter gets me thinking, maybe not.

Has anyone checked the anti-siphon valve on the tank? If this is sticking it will starve the engine for fuel and could be intermittent.

 

[timschap]

Hi, thanks for your reply. I suspected that the "fuel pump test" was a bit funky but not being a mechanic (only a duffer) I did not challenge him. Which I had I might have save myself $1000. I checked the anti-siphon valve and it looked OK. The ball move freely against the spring. I'll make sure he puts the computer on it before he does anything else. He is supposed to be here either tomorrow or Tuesday to replace the fuel pressure regulator. Any other suggestions? This is really getting frustrating ... in my area its tough to get a good mechanic. I'm about 12 miles from the nearest boat yard to I have to rely on mobile mechanics. Should I have him bring a knock sensor with him?

 

[alldodge]

I don't think your issue is a bad knock sensor, as before "IF" the scanner was put on your engine and no codes were found then it would not be a knock sensor, or the wire. You could run the engine without a anti-siphon valve (use a straight brass barbed fitting) just to check things out, it can be reinstalled later if no issue is found.

Ask to see what version of software is on his scanner, it shows up when first connected to the engine

 

[timschap]

We ran the engine off of a remote tank (bypassing the anti-siphon valve) and we were getting the same fluctuation in the pressure gauge (between 25 to 33 PSI as we did from the internal tank. The mechanic said there were no codes (but I'm not sure how good he was/is with the scanner. I'll check with him when he comes to see what version the software is. Unfortunately I'm kind of at the mechanic mercy and I don't have a lot of faith in him. If he does not fix it this weekend there is a certified mercruiser mechanic in a boat yard about 20 miles from me. If he'll work on the boat (I've been told some will not work on engines over 15 years old) I'll have to haul the boat out and take it to him. Its a big pain to do... but I don't see any other option. Thanks for your help.

 

[alldodge]

Getting codes is easy enough but you never know how sharp the guy is. So hope the other guy is better

 

[timschap]

UPDATE. Friday the mechanic change the fuel regulator, Got a constant 33PSI (I felt it was too low). Took it out for a ride and could not get over 2800 RPMs and I "think" I noted a skip.. Saturday for my own satisfaction I changed the fuel filter and put the boat on a remote tank (know good fuel/filter). Same results but no skip. Talking to the "Certified Mercuiser" mechanic to see if he'll work on it (I've been told that some mechanics will not work on engines over 15 years old).

Wish me luck as I've pretty much lost the short New England summer!!!

 

[alldodge]

The 33 psi is on the low side and it might be the pump (mentioned it was swapped/replaced). Your pressure should be higher. According to the service bulletin below, if the pressure drops quickly to zero when the engine is turned off is an indication of the pump.

http://www.boatfix.com/merc/bullet/99/99_08.PDF

 

[timschap]

Update. Took it to the boat yard Saturday. Mechanic looked at it today. Can not figure out what is wrong. Found number 5 cylinder was about 100 psi cold which is low but does not explain not being able to get over 2900 RPMs or having the engine quit all together. Computer log showed the engine was wot. He thinks that if the valve is bad the engine would still get over 2900 RPMs plus does not explain the low fuel pressure. Has a second mechanic coming in tomorrow to look at it. Almost feel like I should just get another engine and drop it in ... very frustrating,

 

[alldodge]

It's fairly easy for the mechanic to test the pump pressure. Merc makes a test fixture which they should have it. There is also an injector balance test which can be done to see if the injectors are leaking. Something is not allowing the pressure to come up fully and that should not be that hard to find. there just is not that many parts.

Maybe suggest this; remove the vacuum line off the regulator and attach to a vacuum gauge. Attach a hand operated vacuum pump to the regulator and pump it to 15inHg. With the engine running the vacuum gauge should read a smooth and steady at 15 to 22 inHg.

 

[timschap]

Update. The mechanic found out that the vacuum was high *about 8 psi) he said it should be around two. He thinks that there is something restricting the vacuum causing the pump to overwork. He said that the spec for the pump is between 35 and 45 PSI. He said that when he undid the vacuum hose to the pump he could get it up to 3800 PRMs under load. I think this is progress. Now what he wants to do is find out why the vacuum is so high (where the restriction is. Since it did the same thing with the remote tank (could not get above 2800 rpms under load, my guess would be some where beyond the fuel filter. Anyway he also suspect bad gas and suggested that I have the tank pumped (the engine has less than 50 hour on it in two years so not much gas has been used). Also wants to send the injectors out to be cleaned and calibrated.

Any thoughts regarding this course of action?

 

[alldodge]

I sure hope you misunderstood the "mechanic" when he said 8 psi is high. The vacuum on an engine is vacuum "inch Hg" not pressure "psi". You should never see pressure on the engine unless a blower is installed. Now if he said 18 and not 8 this would be good, but if it was 8 inHg then this is your problem. A low vacuum reading is signs of engine problems, and if the reading bounces then I would suspect valve guide wear, tuliped (overheated valves) or broken valve springs.

The pump spec at over 60 psi, and this is why when a test is done the pressure should not exceed 60 psi or the regulator can be damaged. The test I mentioned previously with the fixture is to test the max output of the pump.

Removing the vacuum hose off the regulator causes the fuel pressure to go up. Same thing happens when you throttle up, the throttle plates open and vacuum goes down. It's my understanding is that the pump and regulator has been replaced, I'm now suspect this has happened. My largest concern is the current dealer, based on what I'm hearing.

If (and I do mean IF) the engine was run on a remote tank and nothing changed, then pumping the cleaning the tank out would be a waste of time and your money. I strongly think there might be a dart board at this dealer because responses to testing has no basis on reality.

 

[timschap]

UPDATE: The mechanic sent out the injectors. Four were NG and the other four were not worth repairing. Rusted out. Also looked at the fuel rail and it had rust in it. He said the fuel rail was salvageable but he recommended all 8 injectors be replaced. Also he pumped out the fuel tank and said that there was a lot of "junk" in the fuel. He "thinks" that replacing the 8 injectors will "fix" the problems along with putting fresh gas in the tank. Sound right????

NOW to the NEW problem. When coming down off of plane the outdrive oil backs up into the reservoir (and spills out into the bilge). This is a Bravo 3 outdrive ... any ideas? He's a bit stumped about this one. Any idea's?

 

[alldodge]

When coming down off of plane the outdrive oil backs up into the reservoir (and spills out into the bilge).

You really, really ,,, really!!!! need to find another mechanic. Run away while you still have money and a boat. :mad2:

All drives, alpha, bravo (1,2,3) are sealed. The only way for oil to be pushed up into the drive lube bottle is that the seals keeping water out are damaged, or not installed correctly. For it to back up into the bottle when coming off plane means you may not have much of any seals left at all.

 

[Fun Times]

Earlier in the thread you mentioned the fuel rail was "rebuilt"? How so? What parts were replaced?

You also mentioned that after replacing many fuel system parts it seems to run kind of better for a few hours then goes bad again.....Sounds like maybe the contaminants in the fuel was damaging the new components rather quickly.


Normally on this engine model there's a fuel pressure "damper" typically confused as an fuel pressure "regulator" right at the end of the fuel rail......Normally it don't/shouldn't need to be replaced but since you have found a serious problem with the fuel rail you'll want to consider changing it along with the injectors as that could have also been a source of the fuel fluctuation as well as the injectors and/or the lower fuel regulator down by the fuel pump. <Also ensure you are seeing a full 12.3+++ volts on the dash gauge and scan tool with engine both off and running.

The thing is with the fuel pressure damper for your engine is from Mercuiser, it's very expensive at over $300.00....Old Merc part number 802630T and new Merc part number 8M0069803 so it'd be best to see if a GM dealer sells them for less. If not, try to find the GM part number and search online for it. Ask for a 1997 7.4L L29 engine model in a GM truck.

As for the drive oil in the bilge area, before going into the stern drive try ordering a new reservoir cap Merc part number 36-8067271 item number 28,
http://www.mercruiserparts.com/Show...=1943&bnbr=330&bdesc=OIL+RESERVOIR+COMPONENTS

Also be sure the black seal under the cap is in place but most times the orange rubber valve on top of the cap gets damaged which would allow oil to flow out the top of the bottle.....With all the work being done to the boat right now, it would be easy to damage.....Hope it's the cap, good luck.