How to Diagnose Fuel Issues on a KTM 690 (INTERACTIVE)

This started out as a private question on ADV. Here’s the basics of the initial question.

I was honored that he saw my stuff, impressed that he actually took the time to reach out to me, but right off the bat I had a few issues with what he was saying. I wrote a lengthy reply – but then thought this stuff should be public knowledge and not kept private. I’m into the opposite of gatekeeping. Here’s an expanded version of what I had written back to him with links and images.

How to Properly Diagnose Fuel Issues on a KTM 690

The first question with anything fuel related on these bikes is what pressure are you getting? That is the starting point for everything, and the very first thing you should check other than making sure you haven’t run out of gas.

WHAT IS YOUR FUEL PRESSURE?

LIKE IT OR NOT...
If you haven’t checked your pressure then we’re just throwing parts and money at the bike and hoping and guessing one of those things will fix it.

This pressure reading would be taken at the quick disconnect point under the seat, near the airbox. This connection separates by pressing that steel tab inwards.

To take a pressure reading, I recommend the Taco Moto Pressure Tester as it simply plugs in and works inline while the bike is running. https://tacomoto.co/products/in-line-fuel-pressure-tester

Taco Mike should compensate me for all the people I anonymously send his way.

Doing this while the bike is running is crucial so you can see if it’s an intermittent thing, or maybe a loose connection as you wiggle some wires around.

You are looking for a solid, steady reading somewhere from 48 to 52 psi.

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MY FUEL PRESSURE IS…

(pick one, eh?)

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Assuming your pressure is too low or intermittent…

Simply put, low pressure means the issue is on the tank side of things. That makes sense, right?

Let’s start by pulling out the Pump / Filter unit. If you lift up your tank you can easily get to the plate holding it in.

As you slowly and carefully pull the assembly out there is a single electrical 2 wire plug and two special fuel quick release hoses. To release these you need to push the hose in just a little while pulling the connector the other way and you’ll feel it release it’s grip on the tube (female part) and can separate them. One side is fuel pressure, the other is fuel return. The connectors are opposite from each other so there’s no way to confuse them on reassembly.

You should now have this unit free in your hands and able to move over to a work bench.

THE FUEL PUMP

I’d start with the pump first. It’s inside that black plastic housing. There’s two little clips on the side of the black ‘tower’ that you push to release the top from the bottom.

The OEM and most all of the aftermarket ones are built to fail after a certain amount of time. Even AFTERMARKET you say? Yes. And no matter what marketing and packaging might say or look like you’ve probably been fooled. This video is 3 years old at this point but still accurate. Take the 34 minutes and watch it.

Personally I went with the TacoMoto 3,k hour Fuel Pump but even if you replaced yours with the OEM or the ALL BALLS or anything else start with the Fuel Pump. https://tacomoto.co/products/taco-moto-3k-hour-fuel-pump.

IF you can, bench test the pressure that’s coming directly out of the fuel pump. At this point (pump only) we’re looking for around 100 psi. For this you’ll have to pull it out of the tank and separate it from the complete in-tank unit. Or if you have a spare pump lying around, swap it and see if that fixes the pressure problem.

While we’re here, inspect the wiring that goes to the pump. Check the outlet hose for kinks or cracks. Look for loose terminal connections or frayed wires. Check the screen at the bottom of the pump, check to see that the pump inlet and outlet are there (sometimes the ports actually break off) and clear of debris.

THE FUEL FILTER

He had said he had replaced the filter and I assume that was the in-tank one. Technically there’s three. There’s the screen at the bottom of the pump, the inline filter just above the pump and then the little bitty cone filter at the Quick Disconnect. We’ve already checked the screen so let’s move up to the in-tank filter. This is a regular maintenance item that everyone forgets. I would suggest that every time you have to pull the pump out of the tank, you should probably replace the filter while you are in there especially if you are using a cheap filter. I went with the whole package and used the Taco Moto 250 Hour one. https://tacomoto.co/products/taco-moto-co-mother-of-all-fuel-filters

Obviously when you replace your filter, make sure it flows the right direction. Yes, the Taco Moto one is expensive but it also flows 16 times more gas than your bike could handle and does it at 10 microns small!

If your old filter looks like this – you might think you have a problem.
What is all that black stuff? Relax, it’s ground up parts of your motor (brushes) and this filter is intentionally supposed to handle that so nothing to worry but once again, your pump is a wear item – it’s going to wear out naturally.

Moving up the stream of things – if the pump and filter are good – you should see near 100 psi coming out of the filter before it gets to the Regulator if you are bench testing. Check all your hoses for cracks, all the hose clamps for tightness, all the seals and o-rings.

Oh, and make sure you don’t have a kink in one of your hoses. I did that once in putting it all back in. I had a new pump, new filter, and didn’t know I had kinked a hose cramming it all back in the tank. Human error is a real thing and even the best of us is guilty from time to time.

THE FUEL PRESSURE REGULATOR

The Fuel Pressure Regulator on your KTM 690 didn’t come out when you removed the fuel pump / filter. There’s a second panel you’ll need to remove under the tank to get to it. Lift your tank a little more and look just a little more under. It has 4 screws holding it in just like the pump assembly. Here’s the housing (with the pressure regulator removed).

Inspect the wires, the connectors, and the two hoses and clamps running up into this. The fuel pressure regulator is held in the housing by a single screw and a couple of o-rings.

IMPORTANT NOTE: If you are getting a new Regulator – make sure it’s a 3.5 Bar Pressure Regulator.

They all look alike and I have seen people put in higher and lower ones not knowing the difference.

Swapping out the Regulator is easy – just make sure you replace the o-rings with a new ones to get a proper seal.

So, continuing our flow upstream… we should be getting 100 at the filter, and now the pressure regulator should be dropping that down to around 50 at it’s output and that’s what you should see at the quick disconnect.

PUTTING IT ALL BACK TOGETHER

Here’s the complete unit from Fuel Pump on one end – all the way to the Quick Disconnect on the other. Obviously these separate into 2 units to get them in and out of the tank.

Once again, make sure as you reassemble and stuff this all back in your tank you don’t accidentally screw it up and kink a hose or pull off a wire. With the tank and it’s internal parts put back together, add some fuel and check for leaks before running our inline pressure again.

Good to go?
I will assume at this point you have a solid, steady reading somewhere from 48 to 52 psi at the Quick Disconnect.

FUN FACT: Fuel might be flammable but it does not conduct electricity. That’s how we can have all of these open wires inside a gas tank and not explode (usually).

IF your pressure is ok at the quick disconnect…

Let’s start with the Quick Disconnect itself. Let’s make sure the o-rings are good and maybe put a small dash of grease on the fitting so everything goes in and out like magic. You should do the same for the two ends of your Taco Moto Fuel Pressure Tester too!

Next we have that little cone of an inline filter. I replace these all the time and also carry a spare one in my tank bag.

They aren’t cheap but they are a must. Rocky Mountain has them at https://www.rockymountainatvmc.com/parts/ktm-oem-inline-fuel-filter-p

• IF there WAS NOT a big ball of crud plugging up your cone filter I would move on to your Fuel Injector Unit.
• IF there WAS a big ball of crud in your cone filter – you need to figure out what it was and where it came from and how it got in there.

THE FUEL INJECTOR UNIT

From the Quick Disconnect you can follow the fuel line up and it will lead you straight to the Fuel Injector Assembly. It’s a really short hose. There’s a single shouldered bolt that holds the injector in place.

First test I would do is to pull the injector out of the throttle body but keep it plugged in (fuel and electrical). Now turn the key on and push the start button. How does it look for spray? Is it a stream or is it a fine mist? Is there a dribble? Is there a drip? We want to see a fine mist.

Check the o-ring that is on the end of the injector to make sure it seals into the throttle body.

If you are getting a noticeably crappy flow out of the injector you can pull the tip off and see if you can’t just clean it out a bit with carb cleaner and compressed air. Give it a good back flush and see how it flows.

Better yet, for less than $50 – I sent mine out and had it bench tested and cleaned professionally. I can’t bench test as I don’t have the instrument for that. I sent mine to RC Fuel Injection (https://www.rcfuelinjection.com/Store/c/fuel-injector-cleaning) and they sent mine back with the following stats.

While mine was working at the time, their tests showed I was at a flow rate of 305 cc per minute and not at all with a good pattern. This is AFTER I had cleaned it myself as best I could. Sometimes it pays to pay a professional. Oh, and for the record you have what they call a “Hose Feed Injector”.

DOUBLE CHECK YOUR WIRING

If everything checks out, it could always be wiring. Check each and all of the connectors, the crimps, check for broken or loose wires. With a multimeter you should be able to check everything in the fuel system. Is there power to the Injector? Is there a good ground as well? There’s two sides to the story.

I would check each of the connectors for cleanliness and make sure there’s some bulb grease in each. What the hell is BULB GREASE? It’s simply dielectric grease but if you walk into your local auto parts place they may not know what you mean. They should, but you know what I mean. Here’s what I use.

DOUBLE CHECK YOUR SEALS

We have covered a bunch, and nearly everything has a seal. Check each and every little rubber seal along the route, check the big ones too. Speaking of seals – your fuel filler has a seal on it too. There’s also a vent. IF your tank is sealed and you start with a full tank but soon after the bike dies of what feels like fuel starvation – take your helmet off and put your head near the fuel filler. Now crack the filler open – did you hear a slight rush of air? You should not have. Maybe your fuel tank vent isn’t venting and that was your whole problem to begin with. Your fuel tank should be at an atmospherically neutral pressure and not running on a vacuum or charge.

Ok, what did I miss?