Crusader 8.1 - Racor gauge readings

I installed new Racor gauges in an effort to narrow down my surging issue on my Stb engine. I had generic gauges installed a few years ago but they didn’t last and I like the way these new ones “hold” the high reading. As usual, the results are not clear. To recap, my Stb engine has a surge around 1,500 RPM’s of 200RPM’s. It’s a steady up and down. It’s also cutting out at very high RPM’s (near WOT) and the fuel pressure is low according to the numbers I got from my gauge. I have an early 8.1 so it’s just the single fuel pump, not a high and low. The spec numbers I found are not specifically for my year, I’m assuming they would be the same regardless. It’s low at the higher end, idle spec is fine.With the gauges installed, I started the STB engine and the gauge is reading around 2hg and stayed there with some quick revs up and down. Clearly not in the red or even yellow so I thought that was ok. On the port engine, which has no issues, the gauge almost immediately shot into the Red and was 15 with a quick rev up to around 2,000 RPM’s.

That is way into the red on the scale. There is clearly a difference between the two engines but it’s the opposite of what I would expect with a fuel pressure issue. I have two tanks and they’re running independently. I’m not sure what to do next….(This is what the gauge looks like)…. Thanks Bob.


ok, forget all of that! I left the crossover valve closed on the PORT engine when i installed the gauge the other night. That one is reading about 2hg at idle. I’ll compare the two with my next run.

Im not sure and you would have to contact a dealer but there was a pcm reflash for a surging problem on mercruiser 8.1. Maybe it also involved the crusader 8.1.

Gauge readings and description do conflict...any chance the port and starboard gauges are reading 'backwards'? only way that makes sense is the crossover valves work differently that perceived (but just a guess on my side).....

Out of curiosity, did you get values from the old gauges before the update?

inadequate fuel pressure can cause surging....and possible leaness which isn't good for longevity...

i believe your 2" Hg figure is the most pressure drop you want to see and I'd make sure you can maintain that at WOT ideally...the install manual suggested this is at IDLE RPM which conflict with the stated GPH flow...

on the reflash - always a possibility and never hurts to check your current load vs what is available...usually only the dealer has the latest...

Mark,

A couple of quick updates. So, the crazy reading above was a false alarm due to shutoff valve being left OFF when I installed the gauges. Now, I've done a few runs and these gauges do have the telltale indicator which is nice. Probably two hours of runtime including a burst at 4,400 RPM's for 3-4 mins. The high on one side is 5 and the other is right around 4 (it's the exact same gauge in the pic above for reference). Both gauges are returning to zero after shutdown.

Do those numbers seem high to you? As a reminder (to myself as well), I am still running the 3/8" fuel line from the tank to Racor IN. The Racor OUT to tank line was upgraded to 1/2" because of the new configuration. I still have the same floscan setup that I did on the 454's and definitely burning less fuel at all RPM's (I have video before/after). The Port engine is flawless at all RPM's right up to 5,000 and identical fuel setup. The Stb engine has the low RPM surge and I felt it cutting out right around 5,000. I'm wondering if I possibly hit the rev limiter on this one though. I'm also going through some Tach calibration issues at the same time which made me think of the limiter.

Also, the fuel pressure reading was low at WOT on the engine in question BUT the only specs I have found have been for newer 8.1's which have a high/low, 2 pump setup. I guess if my other engine reads the same/close, I can probably rule out low pressure as an issue.

To your question on the old gauges, no I don't think I ever really had those working correctly so no data to compare. I could change one of the filters and use that as a baseline.

thanks for hanging in there on all of the posts!

The pressure drop is more than the spec value....I'm guess the values are the max pressure drop and they occur at WOT?

what is the pressure drop at your normal cruise RPM?

Did you leave the mechanical Anti-syphon valves in? I'd bet they are a major contributor....electrical solenoids are an alternative.

a scan tool would help in seeing if the limiter is invoked...also is the 5"hg drop on the starboard or port?

glad you are making progress...

Mark,

I took it out for a run yesterday. To make it easier to follow, here is the breakdown for each engine:


Stb:

Fuel pressure
Idle: 37 PSI Idle:
Near WOT: 40PSI

Port:

Fuel pressure
Idle: 40 PSI Idle:
Near WOT: 40PSI

(The spec I found is 37-43). Am I close enough? Both pumps are brand new.

Racor reading STB: 1" at idle, 5" near WOT
Racor reading PORT: 2.5"at idle, 5" near WOT (the interesting thing is I changed this filter on the hook to see if the numbers changed - no different)

Near WOT = around 4,400 and not for long. I didn't want to push in case one/both engines are actually running lean. My fuel pressure gauge isn't dampened and the port reading was bouncing around (wife taking readings). The Stb engine was much easier to read a few weeks ago. Either way, I'm not really seeing any increase in fuel pressure as RPM's increase.

My only "symptoms" are still on the Stb engines which is low speed idle surge and the cutting out @ 5k RPM's. (I forgot to check scanner yesterday to confirm that I wasn't hitting redline). Both engines, start, throttle up and otherwise run great.

Yes, I am still using the mechanical anti syphon valves. Do they cause an issue with EFI engines? I've had them out in the past and they were spotless. I didn't come into the repower with any lingering fuel issues. I guess I could upgrade the fuel lines I mentioned next and rule that out.

Open to any other thoughts as well.

thanks

its not the anti-syphon valve itself, its the pressure drop they can induce that is the source of the potential problem...you can just substitute a plain hose barb fitting for testing, if you want to see their contribution to the pressure drop on the inlet...I've see the return type of fuel systems where they caused trouble but that was a few years ago.

the 'normal' change in fuel pressure with RPM assumes the pressure regulator is 'referenced' to the intake manifold (so the injectors see a constant pressure differential. are your pressure regulators plumbed in that way?

the other item i noted was your comment about the gauge not being dampened....and the light bulb illuminated...all 'well behaving' fuel pumps I've seen provide pretty steady fuel rail pressure readings (in steady state)...

Mark, maybe I'll do that... I can even just hook up my external tank and check everything that way. I have the "old style, returnless" (Crusader reference) setup. Just mentioning that because I noticed you said "return" above. In the meantime, I had a few good conversations with Racor and Marine Parts source this morning.

1) Racor tech support didn't think the numbers high or low were a huge concern especially referencing the one new filter as a baseline. The guy I spoke with said there might be a plumbing difference between port and starboard which accounts for the difference at idle. He also went on to say that whatever the number is, that should be my baseline THEN add 7-10" to get my max number. I don't know that I would cut it that close but good to know.

2) On the pump (I replaced both) there is an inlet screen which I left in place. The old pumps didn't have them and according to my contact, there was a bulletin issued way back to remove the screens because they were causing a restriction. I'll do that and will be interested to see if my hg numbers drop accordingly. Man, I hope this is the smoking gun.

- also, they verified that the fuel pump pressure should be around 40 PSI at idle and not much higher at cruise. That's exactly what I'm seeing now. I'm a little surprised by that answer but this is a totally different setup than most 8.1's out there (single pump, no return). I didn't mention my numbers up front and this came from someone who knows the 8.1's since they came out.

I'll get on those screens today or tmrw and follow up.


Bob

I'd be inclined to discount the racor suggested 'too high' value given what crusader specs...granted crusader's number is for a clean system...I'd keep an eye on the engines once the needle shows more than 5"Hg of pressure drop.

interesting on the pump screens...did you clean the screens in the Oberg filters - the hockey puck piece down by the fuel cooler?

on the 40 PSI number - if the pressure regulators are referenced to the intake manifold pressure, then the regulator output should track with the MAP changes...just remember they are typically in different units...I'll add a note to my 8.1 book...tnx...

I eliminated the hockey puck filters altogether since I already had pre-screen filters inline. Out of the tank, I go into a 30 micron screen and from that into a 10 micron filter. I'm really hoping the pump screens are the issue, especially since he specifically mentioned a bulletin. I know they're not clogged, my fuel system is spotless end to end. They didn't pop easily (but are supposed) but I didn't try real hard either.

I agree, now that I have a baseline (I'll change the other Racor as well even though it's fine), I can monitor everything going forward.