951 DI Troubleshooting

[garrettb]

I'm starting a new thread with more specific information on the issues with my 2001 GTX DI. It cranks but will not start. Here is what I know:

-good engine compression
-working air pressure regulator
-working fuel pressure regulator
-good spark
-good spark plugs
-good air compressor
-no blown fuses
-fully charged battery

For some reason, no fuel is being injected into the cylinders. I took both sets of injectors out. They click really well and seem to work as intended when connected straight to 12V.

I rented a fuel pressure tester. Inserting the key immediately yields 27 PSI. When cranking, I am at around 75 or so, the needle jumps around quite a bit. That testing was done with a "T" inserted in place of the fuel filter. With the gauge dead headed on the fuel supply line, inserting the key (no cranking) yields over 100 PSI- it maxed out the gauge.

I have a "maint" light on my dash that doesn't clear, but before I spend some serious dough at the dealer, what in the would could prevent the fuel and direct injectors from energizing? This is crazy, and I am really frustrated with this thing. I am almost upset it wasn't the fuel pump, because that should have been a straightforward fix.

 

[68ragtop]

You might have a few things going on, but it sounds you don't have enough fuel pressure. The gauge bounces when cranking because of the air pump. The fuel pump of course is electric, but its line pressure is determined by the air rail regulator, so you needle will bounce with the compression strokes of the air pump. if you dead head the air pump you should be able to get around 90 PSI while cranking. Dead heading a healthy fuel pump is normally a big dangerious no-no. They can build tremendous pressure in seconds. Well over 150 is possible in 3 seconds & can burst an unrated hose.

Keep in mind the DI injects fuel/air during the upward stroke after the transfer ports are covered by the pistons. So the pressure is rising in the cylinders. The fuel pressure has to overcome the pressure of the air rail to inject & the combined mixture of air & fuel has to overcome the pressure in the cylinders. The Air pressure will normally hover around 80 PSI inside the rail. So if the fuel pressure is at 80, or less, no fuel will be injected. The fuel line has to be 27 (+/-) higher than the air rail pressure to inject fuel to the air injectors & ultimately into the cylinders.

So for now, I would dead head the air pump & see if you can build close to 90 psi cranking. The needle will bounce if its a standard non fluid type gage. If it does hit the mark, put it back in the fuel line. Check for your 27lbs you saw earlier with the key on. Then crank the engine (non flood mode) & see what it climbs to. It should climb to near 100 with no problems. The needle will bounce, but try to take the mid point of the bounce, not the peek reading. Also check your info center, I believe that year will show RPM's while cranking. should be close to 500 iirc.

 

[Coastiejoe]

I also think you may have a couple of things happening..

Fuel pressure is built up when something stops or restricts the fuel. I am not sure, but I think there is an office or something like that in the return line that is what allows the pressure to build up. Your pressure is low. The fact that you exceed 100 when the gauge is deadheaded leads me to think that the pumps are working as they should, but something is allowing for decreased pressure.

Also, buy a mood lamp and hook it to the injector wire harness, it will flash if the signal is being sent to the injectors. Until you KNOW your injectors are being told to open, you are kind of chasing a ghosts..

 

[68ragtop]

The only thing that restricts the fuel pressure is the regulator. no orifice that I am aware of. it's set to release at 27 PSI, but is directly effected by the air pressure. so whatever the air rail pressure is, the fuel regulator will rise 27 PSI above that pressure. If you look at the regulators, you can see a black tube connected to the fuel regulator. that tube is what changes the fuel/regulated pressure. at 75 cranking pressure it makes me think either the fuel pump is weak, or there is less than 80 PSI air in the air rail.

Excellent idea on the injector noids! Coastie, doesn't HF have a cheap noid light kit? that would be an easy way to see if there are injector pulses. :thumbsup:

 

[Coastiejoe]

The regulator is the correct answer,, simply slipped my mind, (not an orifice).

I tend to think his pump is ok as when he tested it as a dead pump (no bypassing of the fuel) it exceeded 100 psi which is the max of his gauge. That said, the OP should use a correct gauge as guessing can be a crucial error.

May places sell mood lamps. I own a full set as well as an adjustable one. I'll post a pic of the adjustable style. Anyone that has an injection system should own one. Super easy to use, very safe, gives excellent diagnosis instantly..

 

[Coastiejoe]

Here is the noid lamp I have,, works great.

 

[68ragtop]

I found an unorthodox way of testing the fuel pump & regulators. disconnect the compressor side of the air line & then attaching a home/shop compressed air regulated at 90 psi. as soon as its hooked up, air will be released (over 80) out the regulator discharge hose & out the rear of the ski. It will basically make a hiss, or leaking sound. Then put the key on & the fuel pressure should rise to 107 & no needle bounce thanks to the steady shop air, its easy to read. When the key is released the pressure should slowly drop & this tests the pumps check valve. if a person has an air compressor & a way to regulate it, this is an easy way to see if pressure will go to the levels they should. & the best part is, a ski will run perfectly using this connection.

of course the fuel pump will only run for a few seconds when the key is put on, but its fine to crank the ski to get the pump to run continuously to see what happens with the fuel pressure.

 

[garrettb]

Awesome suggestions guys, keep them coming. I am going to look into that test light. I am afraid my injectors aren't even being told to open, but more test equipment can solve that!

I bought a gauge that reads 140 PSI, but it didn't get here in time, and when school is an hour and a half from home, I only have a few select weekends to work. Renting was a good start for now, just to get a baseline measurement.

Here is the strange thing regarding the air compressor. When hooked up to my compression tester direct, the engine pumps upwards of 120 PSI in a matter of seconds. To test the air regulator on the fuel rail, I used shop air, and sure enough it opened precisely at 80 PSI. I know I have more than enough air in the rail... so why doesn't my 27 PSI of fuel prime, plus my 80 of air equate to the desirable 107?!?! I can hear the excess air being purged from the rail when I am cranking the engine!

I wish I would have tried to start the engine on shop air, or at least pressure test it that way. If I had a known 80 PSI to the rail, plus the 27 from the fuel pump, and the gauge didn't reflect 107, then maybe the issue is the gauge? Even if the gauge is faulty, it still should have started! I don't know if this information will do anything to change what you guys think is going on, but it should rule out a few things.

 

[Coastiejoe]

To be clear, the NOID LAMP is not a regular test lamp. Specifically designed to not place a load on the system. Don't use a regular test light when testing injection pulse. Many of the new test lights would be fine, but not worth th gamble for how cheap the NOID Lamp is..

 

[garrettb]

It looks like the light you've got is the Lisle Universal Noid Light - 27800. The cheapest one I found on eBay is around $30. It also looks like O'Reilly Auto rents a noid light set, so I may try that first before I buy one. In theory, all I need to do is unplug each of the four injectors one by one, making sure I get light with each connector while cranking? Could a bad/non-functioning injector be the cause of the lack of pressure in the rail when everything else seems good? Then what, faulty MPEM? Oh boy....

 

[68ragtop]

The pressure is unaffected by almost all the electronics. All it needs is 12v to the fuel pump & a normal cranking speed. aside from the voltage to the pump, the rest of the fuel/air system (pressure wise) is mechanical. The easiest test with what you have right now is to check the air pump pressure dead headed, then fuel pressure (in-line, not dead headed) while cranking. If you don't have a pressure higher than 80 its not going to inject fuel.
Not because of the electronics, but rather because your air rail should have 80 PSI in it while cranking. If the fuel pressure is only 75 lbs, nothing will pass out of the fuel injectors.

Thats why everyone talks about 107 fuel pressure being so critical on DI's the 27 PSI you see at "key on" is at the level because the fuel rail is at zero. as you crank the air pressure will rise to 80 PSI normally within a few seconds. now the fuel pressure should rise to 107 80 + 27 = 107 the 27 lb differential is the key for fuel to flow.

Now to complicate things a bit. These machine will run on less than 107, but only if its because the air pressure is less than 80 PSI. But, it will not run if its the fuel pressure thats low.

example #1 air pump puts out 60 lbs at cranking 58+27= 85 fuel rail psi the engine will start up & idle decent.

#2 air pump puts out 80 PSI at cranking 80+5 psi fuel rail PSI The engine will not fire.

My guess is your fuel pump is causing the problem, but that a total guess until knowing a little more about whats going on with the rest of the system.

EDIT: to answer your other question though, the fuel & air injectors will not & should not effect the pressure your reading.

If you had 107 PSI at cranking & no starting I would be more suspect of the injectors or electronics.

 

[garrettb]

I have dead headed my air pump. I cranked for a few seconds and it easily rose about 120 PSI, and probably would have kept going had I kept cranking. Because of that test, I know the air pressure is greater than 80 PSI at the pump, but the regulator only allows it to reach 80 when everything is connected together. Like I said, I can hear the regulator hissing and letting out excess air when I am cranking. That's why I am curious to test with my shop air compressor replacing the one in the engine. Let's say I still only have 75 when primed, with a known air pressure in the rail, that points to a bad fuel pump?

 

[68ragtop]

Just sent you a PM

 

[68ragtop]

Any luck? Did it turn out to be a weak fuel pump?

 

[garrettb]

I haven't been home to work on the GTX yet. Trust me, it's been driving me crazy! I'll be sure to post results when I am able to get to the shop again.

 

[garrettb]

Well, I have an update for all who are curious.

My injectors are NOT receiving any sort of power during cranking. I rented a noid light set, and got nothing. I checked wiring back to AMP 4 to the MPEM, and the wires are good from plug to plug.

Now I am REALLY leaning toward a bad MPEM, or maybe a TPS, engine thinking it is in flood mode and disabling injectors?

Regardless, I am convinced my fuel pump is NOT the culprit. According to the manual, air injectors NOT firing can cause a drop in fuel rail pressure similar to what I am seeing.

This is where my knowledge of this issue starts to become limited. Is there any definitive test to determine wether the MPEM is bad? I did the old "press the start button 5 times, insert key, listen for beep pattern" trick, no faults there.

HELP!!

 

[68ragtop]

Unfortunately the air injectors not firing will not lower the fuel pressure. But to your point, what happens is when the engine is first turned over the compression in the cylinders back feeds through the air injectors because there isn't much pressure built up in the air rail yet. so it does help bring the pressure up at first, but this is only for a second of cranking & after that its irrelevant. It truly does nothing but help the engine start a tiny bit sooner.

Where you able to get 107 pressure at cranking like we talked about? If not, it sounds like you have a fuel pressure problem on top of something else. Keep in mind the fuel/air system is completely mechanical. the MPEM has no bearing on the pressure unless its not supplying 12v during cranking to the fuel pump.

You mentioned you had shop air hooked to the air rail regulated at 85-90 psi. If I was you, I would hook that back up, then supply an outside source of 12vdc to the fuel pump & let it run. your pressure should sit steady as a rock right around 107 depending on your exact air pressure. Your injectors firing will have nothing to do with this pressure. The battery can be out of the ski at the time. just need 80+ air pressure in the rail & 12vdc to the pump. Just be careful to not make sparks when hooking up the fuel pump. I've done this test & I hook a long wire the the pump first & to a battery outside of the ski.

Why your injectors aren't firing is a separate issue I believe, but I wouldn't skip over one thing & look at another. multiple problems at the same time can be like solving the rubix cube with a DI

Did you say the maint light comes on right after you put the key in? Could be something like the cps sensor not sending a signal, that would prevent the ejectors from firing, but still wouldn't effect the fuel pressures your seeing. Hows the connector look that plugs into the front of the mag cover?

Also, the button push doesn't get codes on these skis. no way to get the faults on DI's without a Buds or Candoo. I'm guessing you looked over all the sensors & there connections? TPS (1&2) map, mat, exhaust temp, engine temp, knock sensor, etc.

Based on what we know, it sounds like you have two things happening right now.

 

[garrettb]

Alright, I have more strange news. Apparently the fuel pressure gauge I bought on eBay is junk. When I inserted the key, nothing happen on the gauge until I took it off and put it back on about 4 more times. Then I finally got the gauge to show 26/7 PSI.

When cranking with the compressor on the engine, it slowly rose to around 55 psi, but that was after 7 seconds or so. I didn't want to fry my starter. Gauge is definitely crap.

If my logic is correct, running the rail off my shop compressor, and inserting the key should give me 107 PSI on the spot without any cranking. My stupid gauge read 0...

I am going to go back to O'Rilley auto tomorrow and rent the gauge I used the first time. I know it's only a 100PSI gauge, but at least this will make it clear if I can peg that gauge or if I still only get 80 PSI while I am cranking.

At any rate, you're probably right that I have two issues right now. I will test my CPS and other sensors tomorrow. Yes, the maint light is on whenever the gauges are active.

I am so determined to get this thing going, and getting that old fuel pressure gauge might be a start in one right direction. If I solve my pressure issue, I'd like to think I only have one more issue left. ha!

 

[68ragtop]

Yes, you should be able to get 107, but the pump as you know only runs for a few seconds. There is a check valve in the fuel pump, so even if you can't build 107 on the first try, it should hold its current pressure long enough to re-insert it & see if it continues to climb. But, a healthy DI pump can build pressure fast, so it should happen in the first try second for sure.

Put your gage against a known good gauge on your air compressor line to check it. pressure is pressure regardless if its fuel or air.

what I like about testing it this way is you don't have to have your engine cranking & your needle on the fuel gauge will no longer bounce 10 psi with the compression strokes of the air compressor.

 

[garrettb]

I've got a link to a video I took to help illustrate what's going on. My conclusion to issue #1 on this GTX is a bad/weak fuel pump. Carl, your trick yields the same result on the gauge. It flutters around 95, then slowly drops and holds at around 80 with shop air connected to the rail.

https://youtu.be/W1Buubjc9pw

My CPS is good, as I can see the 500 RPM while cranking. I don't know where else to go regarding the injector issues though.

 

[68ragtop]

The drop is after the pump stops after the 3 second prime. How much pressure are you feeding to the air rail. are you keeping it in that 85-90 psi range? you basically want it high enough where the air regulator is releasing and is hopefully sitting around 80 psi. sound like a lot of air is escaping. harmless, but will drive your fuel pressure up higher. maybe 110+

A pressure gage in the air line at the same time would be ideal, but not sure how many gages you have on hand.

Other than the needle being a little jerky, it got to 100 as quick as it should, but you might want to re-insert the key right away a few times & see what it does. its only going to run for 3 seconds when you put the key on.

 

[garrettb]

I am probably giving it 90 PSI. You can hear the constant hissing in the video, that's the regulator in the rail releasing the excess pressure to keep it regulated at 80.

I really wish I could just be able to start the darn thing and monitor the pressure that way. It would be so much easier! Theoretically, if I had firing injectors, it would start at the pressure I am observing.

I am not too far away from a BRP dealer, so I think I'll just have them scan it. I need to find out why it won't energize the injectors, and I am out of answers. I'll try to keep you guys posted for anyone else who is having issues similar to this.

 

[garrettb]

I figured I'd give an update for anyone interested. New MPEM, same results. I am now thinking it's wiring related, so I ripped the old engine harness out and have a new one on order. If this doesn't fix it it's going to the dealer to get scanned!

 

[jamiepdavies]

Good luck [emoji106]

 

[garrettb]

FIXED!

The $24 used harness I scored from eBay did the trick! After all this time, I feel a little stupid for not trying something so simple right from the start. My maintenance light is off, and the sound of the injectors ticking is oh so satisfying.

Before I attempt to start it, I want to pull the engine and change out the counterbalance oil. While the engine and gas tank are out, I would also like to get rid of all the black grime on the inside of the hull. I have a power washer, but I have a feeling it won't be that easy. Any tips?

The next question becomes, which one do I keep- my 2000 blue GTX (carb) or this 2001 red GTX? Or sell both and get a newer 4 stroke? My dad loves his 4-tec Wake 155, but I beat him out of the hole and at top speed in my blue GTX. Ha!