Mercruiser 170 new fuel pump defect or operator error?

[newbieboater1]

Hello all, and thank you for your time. I have a 1985 Century Palomino that I spent three months replacing the stringers, transom, etc.. However, this is an engine related question. My engine is a mercruiser 170 (yeah, I know its not a great motor, but it used to run great). I originally suspected a fuel delvery issue, but I was wrong and it was the carb that needed rebuilt, (but during my troubleshooting I bought and installed) a new fuel pump for it anyways. The new pump lasted approximately 16 hours before I began losing fuel pressure (I have a pressure gauge between the pump and the carb). The higher the engine RPM's, the lower my fuel pressure got (until popping/backfiring through the carb). I suspected the carb again (this carb has been a pain). However, when I tore the carb apart it only had a small amount of fuel in it, and when I pumped the throttle I only got a small rickle of gas from the jets. I suspected a line blockage, and ran the fuel pump directly to an external tank, but with little success. It would pump fuel, but not enough. Then I though that I should inspect the new fuel pump. Perhaps I installed it wrong. When I removed it from the engine, I found deep scarring (and severe wear) on the armature, and my cam lobe is nearly completely scored off. I know that the cam lobe was nearly perfect before I installed the pump because I inspected the lobe for damage after suspecting the old fuel pump for problems. I did note that the new fuel pump armature was radically different than the original, but NAPA told me that this is the correct pump for my engine (yes, it is a marine pump). I have included some photos of the original pump, and the new pump.

The first photo is of the two different pump arms, and the second photo is of the scoring on the new pump arm. The original pump's arm had very little
(if any) wear (and for being 20+ year old, I thought it was in great shape).

Napa and the local mercruiser dealership have no clue as to why this happened, do any of you? Please forgive me if I am confusing and/or incomplete.. My kids are running around trying to kill eachother while I'm typing this.

Thanks again!

 

[Alpheus]

Re: Mercruiser 170 new fuel pump defect or operator error?

Looks like the angle of the pump arm is wrong and it was not riding on the cam in the correct orientation. Looks like all the pressure was pushing on the corner(bend) instead of displacing the pressure over the face of the arm. I wouldn't have put that pump on there. What does the NAPA guy know except what a number in a book is telling him...

 

[newbieboater1]

Re: Mercruiser 170 new fuel pump defect or operator error?

there is no "straight arm" version available. I spoke with my local mercruiser dealership, and they told me that the new pump is the correct one, but they also told me that this pump has never changed from the original.. But it must have.

I'm really confused about this

 

[Alpheus]

Re: Mercruiser 170 new fuel pump defect or operator error?

Either way your cam is toast. Change the oil and filter,put on a block-off plate and install an electric pump...

 

[newbieboater1]

Re: Mercruiser 170 new fuel pump defect or operator error?

I agree that the electric pump is my only option at this point, but what do you think the odds of some of those shavings finding their way into my bearings are?

 

[Alpheus]

Re: Mercruiser 170 new fuel pump defect or operator error?

The oil filter should have picked it up...

 

[newbieboater1]

Re: Mercruiser 170 new fuel pump defect or operator error?

oops. I was typing while you were.

Should NAPA be partially responsible for this issue?

 

[stonyloam]

Re: Mercruiser 170 new fuel pump defect or operator error?

Are you planning on adding a oil pressure safety switch, with the electric pump?

 

[newbieboater1]

Re: Mercruiser 170 new fuel pump defect or operator error?

I suppose at this point, I have no other choice...

 

[EddiePetty]

Re: Mercruiser 170 new fuel pump defect or operator error?

....your new pump appears to be a Sierra P/N 18-7282 (which NAPA sells). Much to my surprise it crosses directly back to a Mericruiser P/N 42725A3 that I believe fits your boat.
The Sierra appears to require a spacer between the pump and block to limit the stroke length. Measure the distance from the mounting flanges of each pump to their respective wear pads. Notice that the Sierra has a shorter moment arm?.
If the fuel pressure gauge was installed with the Sierra, you should have noticed excessive fuel pressure...prior to the pump's diaphram bursting.
Sadly, in agreement with the clan, short of a camshaft replacement, there is an electric fuel pump, blanking plate and pressure switch in your future.

 

[newbieboater1]

Re: Mercruiser 170 new fuel pump defect or operator error?

Who would have thought that replacing the fuel pump would cause these issues? Is there anywhere that i can point the finger, or is this my fault?

I don't believe that the diaphram ever ruptured, but the output fuel pressure kept becoming less and less.

Should I ask NAPA for a refund? The pump is almost new.. Perhaps they can exchange it for an electric?

 

[Alpheus]

Re: Mercruiser 170 new fuel pump defect or operator error?

Couldn't hurt...

 

[newbieboater1]

Re: Mercruiser 170 new fuel pump defect or operator error?

Thank you all very much for your help and advice!