Fuel Pump Cuts Out

[Jim Garry]

I’m hoping the community can offer some ideas on a problem with my engine. It’s a 2005 Suzuki GSXR 1000 in an autocross-only sports racer (a Cheetah). This is the 3rd year running this engine. Had cooling issues in previous years but those have been resolved. A new problem began this summer. In the first few runs of the day the engine is fine. But as the engine bay heats up, the fuel pump begins to cut out. At first it’s just a hint. But with more runs and more heat it gets worse and the engine cuts out more often and for longer on ensuing runs.

At one event the engine died while idling in grid and despite good cranking power it would not start until we let it sit for 10 minutes. Later, for last run it died again while waiting at the start line (after a long delay). Good cranking power but wouldn’t restart. My co-driver got a peak at the fuel pressure gauge during my cranking and noted it was at zero. Later, it restarted fine.

This past Saturday it was fine on a very short (23 second) test course. Took a dozen runs in 30 minutes. But it was not a heavy throttle course. On Sunday there was a long course with lots of long throttle sections. First few runs, again, were fine. Last run of the morning hinted at a very brief fuel cut out. We were back at it two hours later. First 2 runs of afternoon had one solid cut out each. Then with more runs, we experienced more cut outs until the last few runs of the day were incredibly compromised with many short and long fuel cut outs.

Here’s a video taken showing the fuel pressure gauge during one of those runs. In this one minute video the engine cuts out 3 or 4 times. https://youtu.be/NXRGPwCu4FU (The loose bolt you can see on the right doesn’t need to be there and will be removed. The gold covered line also on the right will be secured.)

Over the last few events I replaced the crankshaft position sensor and fuel pump relay. No help. Since the last event I replaced the 2 year old Bosch 044 fuel pump with an identical brand new one and will test it at the next event. But I don’t think that’s the issue because everything runs fine until the car heats up. Wouldn’t a fuel pump problem be consistent? Or can a fuel pump get fritzy due to heating up too much? The fuel pump location is less than a foot from one of the headers. At the last event I shielded it with commercially available heat shield material but it didn’t help.

Based on how fast the fuel pressure drops and how quickly it recovers (see video) it does seem like it has to be an electrical problem, yes? And the electrical system is over-taxed. Voltage below 11.8 will cause engine to misfire. But this situation isn’t a misfiring. This is loss of fuel pressure for ½ to 2 seconds per shot. Wouldn’t a battery voltage problem show a lot slower pressure drop than what we see in the video? Battery is brand new.

It looks like the engine is losing all or most of the voltage to the fuel pump momentarily and then it comes back again. So there’s an intermittent connection occurring but only with the addition of heat. It won’t happen on the first 3 or 4 runs of the day. I’m flummoxed.

I don’t see any loose connections or bad grounds or broken wires but I haven’t removed the wiring harness for a detailed examination. And has anyone experienced a bad connection/ground/wire only making itself apparent after the heat created by running the car for a while?

Another variable is that at some point this season I added a heat shield below the stock air intakes to try to reduce heat into the intake. So engine compartment temps might be higher but it’s not like it’s a sealed engine compartment. And even if it did heat up more than in the past, is there a component (fuel pump???) that just can’t take that extra 25 or 50 degrees? Yet I can’t ignore this factor. My plan is to run the car next weekend with the new fuel pump. See if the problem occurs. If it does, I’ll remove the heat shield (it’s just an 032 piece of aluminum above the headers and below the stock air intakes. Or should I just remove it right away? Then I wouldn’t know if that was the winning move or the fuel pump change did the job.

I’m wondering if I should just go ahead and get a new wiring harness.

Any thoughts on this issue will be much appreciated.

[BLS]

Sounds like vapor lock to me. I would reroute and protect the fuel lines/pump from the heat.

[Gary_T]

I'd be surprised if it isn't the fuel pump.

If you want to be sure on the voltage, put a light/volt gauge in view of the fuel pressure gauge on your next recording.

Good luck!

[FASTDAD]

Could it be a fuel cavitation/pickup issue? Take notice if it has this issue after any particular directional change.

[RussMcB]

Good job with the camera. That certainly points you in the right direction.

Is it possible your pump is sucking air? Or, for some reason it doesn't have a good, non-restricted flow of fuel to it?

Any filters (or other restrictions) between the cell and pump?

Is the pump mounted low and near the fuel cell (so it doesn't have a long pull)?

I'm not sure if it is worth the trouble for you, but all of my road race cars have had a Facet low pressure pump feeding a small reservoir, which is the supply for the Bosch 044. It pretty much guarantees the Bosch 044 will always have a supply (until all of the fuel is gone).

I like the idea above suggesting a temporary warning light to indicate if there is a loss of electricity to the pump for some strange reason.

Can you consistently replicate the problem at home? That will help tell you if a change helps.

Good luck.

[Jim Garry]

Thank you all for the suggestions. Russ, the pump is low and right next to the cell. There is a filter just prior to the regulator, it's been changed recently. Can't replicate this condition until the engine gets hot on the pavement with load. Won't go wrong while idling, even allowing it to get hot. Would need to rev it hard anyway.

I'm now thinking it has something to do with a bad wire in the harness or a bad signal for some reason from the ECM. So I'm going to cut the ECM out of the loop and wire the fuel pump to a switch on the dash, getting power from a fused source.

Thanks again,
Jim

[Daryl DeArman]

Other than all the suggestions I've heard mentioned above, maybe take a look at the check/tip over valve in the fuel cell vent line.

Next time you get a hot/no start situation check for voltage at the fuel pump. If adequate voltage check fuel flow. If fuel flow is inadequate remove fill cap from cell and see if the problem immediately rectifies itself and doesn't require the car to "cool down".

[BeerBudgetRacing]

Heat does funny things to electrical connections.

Had a starter that worked fine in pit, on grid, and even on track, but when I sat in impound the heat soaked in and caused a bad wire to separate under insulation.

I'd do the voltage checks suggested. Or even a simple resistance check of the wires.

Good luck.

[924RACR]

Had a somewhat similar issue to this in my '08 GSXR car, where it'd only go about 3 laps on track before shutting down; finally noticed that voltage to the pump was indeed fading with time/heat - observed with engine running, directly logging engine data from the engine ECU.

Resolved by rewiring away from the stock wiring/harness, going to dedicated power (switched on dash, Mil-spec toggle) for engine ECU and fuel pump, more substantial wires than stock. I wanna say like 12ga, whereas the stock wiring was rather light.

Different year, but... yeah, rewire.

[RussMcB]

I use the fuel pump wire from the ECU/harness to trigger a relay, so the fuel pump gets a strong 12v from a bigger gauge wire.

[Jim Garry]

Since this car is now for sale, I thought it would be wise to post the results of my efforts regarding diagnosing the problem described in this thread. Actually, even if I was keeping the car this is something I should have already posted. My apologies to all.

It turns out to have been a voltage problem, as many suspected. Prior to the start of the season, a new fan was installed for radiator cooling. It used a few more amps than the previous fan but was more efficient too. With this additional load, the alternator couldn't quite keep up and so the battery was losing a little voltage throughout the day. By later in the day, the ECM would rebel due to not having enough voltage.

The small voltage loss still probably would not have caused an issue but for a relay that connects two fuse blocks. That relay was not beefy enough and there was almost a volt lost going through it. A better relay eliminated that problem which in turn eliminated the engine cutting out.

Thank you all for your advice.