951 DI Pressure Regulator questions

[Lee.]

Hi all, first post so hello :thumbsup:

I apologise for the long post but I'm trying to get all my thoughts down to avoid any grey areas, for those of low attention span, the important part is the last paragraph!

I've bought a 2001 RXDI which came in a box of bits, it's all been nailed together and I'm not at the stage where I'm trying to get it running but it doesn't want to play ball. After a lot of reading, digesting the manual, testing pressures, injector pulses, sparks etc I'm at the following point;

The ski will not start without intervention. Pouring a little fuel into the bores will allow it to start and run until the fuel is used, then it stalls. The Air and Fuel injectors spray when disconnected from the head and the engine is cranked, but when fitted, engine is cranked, then fuel rail is removed, the bores seem to be completely dry.

Regulated air pressure at the fuel rail is ~76-80 PSI (as per the manual) although the gauge I'm using has a sketchy scale but seems reliable in measurement. When the return pipe from the regulator is pinched, the pressure rises well over 100 PSI before I release it, then returns to a consistent 76-80 PSI which tells me that the compressor and regulator are working as intended, washing up liquid and water poured over all joints and pipes shows no leaks.

Regulated fuel pressure fluctuates wildly, I think this may be where the problem lies. When the DESS key is connected, the fuel pressure rises to anywhere between 27 and 60 PSI without the engine cranking, when the engine is cranked, air pressure goes up to the regulated ~76 PSI but the fuel pressure (which should be, in this case 27+76=103PSI) never goes above 80 PSI and the engine will never catch.

Now the caveman testing starts, pinching the air return hose to the point where the air pressure goes over 100 PSI will cause the fuel pressure to rise to slightly over 100 PSI when cranking, if the air return is then released, the engine fires and runs for about 5 seconds and then the fuel pressure drops below 80 PSI and the engine dies.

Other than checking for leaks between the air regulator and the fuel reg, I'm pretty stuck on where to go next unless I can use a fixed fuel pressure regulator to set the fuel pressure at ~107 PSI to prove the fuel regulator or something associated with it is faulty. What is the reason for the rising rate regulator in the fuel rail and will it cause any problems if the 27 PSI priming phase is skipped in favour of a straight regulation at ~107 PSI?

Thanks for reading, look forward to your replies.

Cheers, Lee.

 

[Coastiejoe]

I don't know enough about the DI engine to give you great detail other than, you need 107 psi of fuel pressure for it to run. And that fuel pumps are Avery common failure.

 

[jhjesse]

Which side of the fuel filter are you putting your gauge? Pump side or fuel rail side? Reason I ask is because, you could have a partially clogged filter preventing max fuel pressure.
Have you pulled the pump and changed the internal filters directly on the pump? There are two filter socks connected directly to the pump that over time get clogged. Good luck.

http://www.seadooforum.com/showthre...Direct-Injection)-Fuel-Pump-Replacement-Guide

 

[Lee.]

Thanks for taking the time to reply.

CoastieJoe - 107 PSI is what I'm shooting for as per the manual but I'm unsure how critical this is, ie would it still run at 100 PSI?

jhjesse - Line filter has been removed for testing and the pump socks look clear, I can get >100 PSI but only when I fudge the air pressure to be higher than the specified 80 PSI hence why I think it might be something to do with the regulator.

Cheers, Lee.

 

[jhjesse]

Air pressure - good
Filters - good
Fuel pressure - fluctuates

My guess would be the regulator as you suspected. Fuel pressure should be constant. Have a 2000 GTX DI that did the same thing. Replaced the regulator and fixed the problem. Hope this helps.

 

[68ragtop]

One thing to keep n mind when watching fuel pressures, is the fuel pressure is directly effected by the air pressure. (as your finding out) In a correctly functioning system the air pressure will remain in the rail after its shut off. It can stay there for a very long time if your air pump reeds & regulator are in good shape.

The fuel regulator is fixed at 27 psi like you said, but it has an air port that allows this regulated level to raise by whatever the air pressure in the rail is at. So, you could have had the engine cranking with some residual air pressure still in the rail. When you install the key, your pressure will raise by that amount.

An example would be: Air pressure is sitting at 50 PSI, you install the key & the fuel pump runs, but the new fuel pressure regulation is now at 77PSI, The only time you will see 27 PSI is when there is zero air pressure in the rail.

The other thing that makes fuel pressure hard to read is the air pressure while regulated at 80 PSI, it pulses with the air pistons cycles. so at cranking speed the needle will bounce pretty wildly. This bounce can be seen in a normal running engine too, but at 1450 RPM, it looks more like a like a vibration & is easily read.

The problem with this system is the combined pressures have to be able to overcome the compression being created in the cylinders as they are coming up to TDC. If the pressures are low, its not going to be able to inject anything. If the spark plugs are pulled, or the rail is removed it will spray fuel all day long at lower pressures.

Just out of curiosity what are you finding for compression on this engine. you said it was in pieces, did you rebuild it?

If you are only getting 100 PSI of fuel pressure, I think its a little too low. Too low to run? maybe. Also, make sure your gauges are very accurate. If you can, test them on a shop air line to compare with other gauges. If a gauge gets dropped at some point, there a really good chance its no longer accurate.

We need to good a good reading not his pressures you have.

 

[Lee.]

jhjesse - That's what I was suspecting, the ski had been sat in pieces for a while so I can only assume the petrol left in the reg varnished the internals up and it's gone 'sticky'.

Can I use a fixed regulator at a constant ~107 PSI or does it sit at 27 PSI on priming for a reason? I can't see any particular reason other than 27 PSI is the offset above air pressure so it's just a product of the regulator design.

68raptop -

The problem with this system is the combined pressures have to be able to overcome the compression being created in the cylinders as they are coming up to TDC

This explains a lot thanks, I wasn't sure if the fuel was injected on the compression part of the cycle although surely it would have to overcome 120+ PSI on a serviceable cylinder? Engine has not been rebuilt in my ownership, it was bought as a known runner (maybe...) from a friend and I haven't got around to testing the compression although with the faintest sniff of fuel it's away and sounds sweet enough.

Residual air pressure in the lines/rail were taken into account when testing, gauges are verified as more accurate than most things available on fleabay :biggrinjester:

Best fuel pressure without intervention (falsely raising pressure through fudging air reg) was around 80 PSI, I think this is due to a duff fuel reg but would like an opinion of the likelihood before spunking money on one.

Cheers all :thumbsup:

 

[68ragtop]

I have a pile of gages as I have been doing auto body work for years (as a hobby) I have had higher end devilbiss & Binks gages be off more than 10 PSI. Some of the good ones can be taken apart & be re-calibrated. I have found a Healthy DI engine can run 140 to even 145 PSI. much higher than its carb'd version 951 partner. I have one gauge I know is accurate & I only use it to test it against my other ones.

But the machine should still run at 120, so that doesn't sound like an issue at this point.

If you put a fuel pressure gage in the line, crank the engine over (without putting it in flood mode)
you should see the pressure rise to 107ish while cranking, but the needle will be bouncing from something like 100-120
you should be able to calculate the mid point of the needle bounce however. Hope this makes sense.

If you want to see it really accurate, disconnect the air line from the pump & supply it with 90+ compressed air from your shop. The fuel pressure needle will sit like glass & on a correctly functioning system, the engine will start up & run on the shop air.

 

[Lee.]

Fuel pressure never goes over 80 while cranking, thought about supplying it with air from the compressor but as it measured out to the manual spec's I didn't want to add another variable into the process. I am getting a measured ~80 PSI from the compressor but fluctuating fuel pressure so I'm inclined to think that my fuel reg is borked.

 

[68ragtop]

Could be....

The idea of air pressure to the regulator was more to eliminate a variable by creating a know pressure, not to add one.


But, as it is now, If you release the air pressure from the rail & then have 27 lbs, at key on, I would not be super quick to blame the fuel pressure regulator. Also, when you have put the key on, the pressure should hold at no less than 25 lbs for an extended amount of time after the pump stop running/key removed. I would not be surprised to see a healthy system hold fuel pressure for 24 hours or more. If it drops back down quickly there is problem.

Its very possible your fuel pump can create the 27lbs, but then as the air pressure raises the regulator to 107, the pump can't do it.

but the bottom line is, if you have 80 psi of regulated air pressure at cranking, but under 100 PSI of fuel pressure at the same time you either have a bad regulator, or a bad or restricted fuel pump. These pumps are known to get plugged up & filters & are replaceable in the baffle if needed. If you isolate the fuel pump, be careful, in proper working order these DI pumps can make well over 150 psi if dead headed, or if you block the return like you did with the air pump.

 

[Lee.]

Happy Sunday folks!

Apologies for the delay in replying, life has a habit of keeping me out of the garage! First off, massive thanks to everyone that replied, I think I've dropped onto the problem and can now look at resolving it.

Stripped the pump unit out of the tank today and short circuited it to check the unregulated pressure and it turned out around 90 PSI. As I remember the pump being an aftermarket one when I saw it on putting the ski together initially, I decided to strip the pump out of the canister to check the sliding seal replacement (two jubilee clips and a piece of fuel hose...) for leaks.

I now had the pump, a short piece of hose and a gauge sat in a container full of petrol ready to see fuel pissing out of the hose when I connected the power up, instead I noticed the pressure go up to around 90 PSI and then start bypassing through a small drilling in the bottom plate.

After a little reading, apparently this is a common problem with some of the cheaper pumps and the OE didn't need this due to having a return pipe from the fuel rail. Some people have successfully blocked off this bypass and gained the necessary pressure to get their ski running. Anyone have any thoughts on this?

Cheers, Lee.

PS, the pump has E3034.1 etched onto the side, I assume this is a 'HiFlowFuel' chinese special? Apparently this was fitted by a reputable business, rough bastards.

 

[Coastiejoe]

Most aftermarket pump simply will not hold up to the demand that this ski/engine requires. There are a couple that I have read about here at the site that many are happy with, but I do not recall what they are.

 

[jhjesse]

Glad you located the problem. Now get it fixed and go have fun.

 

[68ragtop]

I would give some thought to a used oem pump. Risky? yes it is. But if its healthy you might be better off.

If you go that route I would try to find one thats for sale where the seller is parting out a machine that has failed from some other catastrophic failure like a junk crank. I have bought a few really nice parts this way & didn't have to over pay at the same time. There are a lot of really good big quantity sellers out there too, but I wouldn't buy a used fuel pump from one of those guys unless they have a good reputation & will stand behind it if its no good.

So many of these skis that are parted out, are being parted for unknown reasons, so for all you know, the pump is why it became a parts ski in the first place. There's a bunch of members on this site that part out one at a time & it might be a little easier to tell what the skis were before & what took them down. Then there are also guys like Tonka that sell in large quantities, but is one of the rare guys that won't just sell every part to make a buck. he makes sure they are worthy or he doesn't bother.

there are options, just got to be carful. I would take a used oem unit over an aftermarket any day.

 

[Lee.]

Small update. I made a typo in my last post, pressure was actually 80 PSI when the pump was shorted which is the same as I have been getting all along, even with the reg in circuit. Decided as the pump is essentially scrap I'll bodge the bypass closed as it's not really necessary (or present in OE) for this type of system. One interference fit alloy slug and some chemical metal (JB Weld to you guys over the puddle?) Later and we have 104 PSI and a chance at a running ski when it's all nailed back together.

I'll report back tomorrow when I've tried it out.

68ragtop - I'm in England so parts are a bit harder to come across and I was brutally raped on import duty last time I ordered from the states so I'm loath to try again! I'll be keeping an eye out for a good used one and I have my test rig to check it now.
What causes the death of the OE pumps? I'm lead to believe its moisture in the fuel? Does ethanol have any impact on the lifespan?

Cheers, Lee.

 

[68ragtop]

Really not sure what tires the pumps to their end, but my theory would be their sheer strength could be a factor? the things produce twice the pressure of an average fuel pump & are no larger. So, it could be they just wear out quicker. for sure contaminated fuel could play a part in it would think. It sure seems to in every other aspect. I do believe that many of these oem pumps also get scraped because of plugged filters tho. My first DI had a what seemed like a bad pump as it couldn't supply enough fuel to keep the engine running, however it did start up ok.

Turned out to be plugged filters & it was all good after the change out. Those two filters in the baffle are replaceable & there is a check valve in there that needs to work correctly as well. I suppose its also possible that the check valve fails in the bottom of the baffle & the pump starts pulling fuel away from the baffle & the pump overheats & fails?

Someone else may be able to shed more light on the pump failures.

I also found out through some tests that these machines will start & run on lower air pressure, but not lower fuel pressure. The injection system doesn't need the full 80 psi of air injection strength to start, but if it doesn't have the 27lb higher fuel pressure over the current air pressure, the fuel will not leave the fuel injectors & all that will get injected into the engine is air. obviously this is what you've been experiencing.


I was able to start one of my DI's with only 50 psi of air & 77lbs of fuel pressure. (30lbs low) but if I would have had 65 lbs of air & 77lbs of fuel it would not inject any fuel. I have been playing with these things a little more as of late with the start of your post & another member who has been having a similar problem.

fuel pressure has to be high enough to overcome the air pressure, the air pressure has to be high enough to overcome the pressure in the combustion chamber. Pretty cool system when it works.