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fuel injectior flutter on race engine

fuel injectior flutter on race engine

(OP)
We are racing a Duratec 2.3L, 4 cylinder engine and are experiencing a problem with the engine that at the 6000 to 8500 rpm range the engine will stutter and act like it is misfiring. All of the ecu traces except the injector,shown as time injector is on, and rpm are smooth and look normal. The injector and rpm trace change from a smooth line to a series of short up and down traces that look like static on a dc voltage trace, that correspond to the problem of poor running. We have tried various crank triggers, MAP sensors,lambdas,and temperature sensors. Have had different fuel maps different ecus tried, with no change.I am thinking we have a bad wiring harness or connector, but can not explain why it would only show up in the upper end rpm range.

RE: fuel injectior flutter on race engine

Is it a stock ECU? Could it be as simple as a rev limiter, but not limiting the revs very effectively due to your other mods?

Just a thought. Likely not correct.

RE: fuel injectior flutter on race engine

Could this be related to sample rates and control loop response time?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: fuel injectior flutter on race engine

How about putting an oscilloscope on the injector leads?

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: fuel injectior flutter on race engine

" All of the ecu traces except the injector,shown as time injector is on, and rpm are smooth and look normal."

What is the source of the "rpm trace"?

Look at the scope trace on each connection to the ECU. Do any others exhibit extra pulses under the abnormal conditions?

Injector traces can be difficult to interpret due to pwm current control. The other thing to avoid is triggering the scope with the injector trace itself. (It becomes difficult to determine whether the problem is interruptions to the injection pulse or additional rogue injection pulses. Use the TDC or cam sensor for scope triggering if possible.

je suis charlie

RE: fuel injectior flutter on race engine

It sounds like the root cause is the rpm signal going unstable.

RE: fuel injectior flutter on race engine

(OP)
Thank you for all the ideas, for VE1BLL the ecu is a Pectel racing unit,EdStainless sample rate and control loop are set by the ecu, Hemi oscillascope is not withme,gruntguru,traces are stored in ecu and downloaded mto a loptop,and LionelHutz,we tried and ecu from a running car and had the same symptoms

RE: fuel injectior flutter on race engine

Can you get injectors with less inductance?

Mike Halloran
Pembroke Pines, FL, USA

RE: fuel injectior flutter on race engine

Still curious as to what the "RPM trace" actually is. Is it a crank sensor, or some ECU generated signal for a tach or such? Come to think of it, does your tach behave itself when the engine is misbehaving?

Check the wiring from your crankshaft sensors and ensure they are not running too close to high-powered output wiring such as injectors or ignition primaries.

Can you post a picture of the faulty traces?

je suis charlie

RE: fuel injectior flutter on race engine

Well, one factor used to decide how much fuel is injected will be the engine rpm. So, an unstable engine rpm that is fluctuating will cause the pulse width of the injectors to fluctuate. Unsuccessfully testing with another ECU points to the rpm pickup being the issue.

As to why it acts up at a higher rpm? It could be vibration of the pickup or the pickup can't cleanly switch at the higher frequency or some other cause.

RE: fuel injectior flutter on race engine

The OP has swapped the ECU and a whole range of sensors which suggests wiring harness - either bad connection or crosstalk.

Never rule out non-electrical causes - even when you think you see a faulty trace. Your symptoms suggest something like a broken (inner) valve spring.

je suis charlie

RE: fuel injectior flutter on race engine

Uneven pressure or resonances in the fuel rail?


Norm

RE: fuel injectior flutter on race engine

(OP)
Thanks for all the great ideas but because we were just not able to be competitive, we withdrew from the event. The problem is in the wiring harness and when the throttle position sensor(tps) reaches a point in it's travel, the injectors stop being triggered by the ECU. This happens no matter what speed the engine is running at,and this was proven by using another TPS,and setting the rpm by opening the butterflies, and then turning the tps with a screwdriver. We have tried three new tpss units 2 of them Ford OEM parts and one aftermarket with the same results.

RE: fuel injectior flutter on race engine

What is the signal characteristic of the TPS? 0.5 - 4.5V, PWM, frequency? Is there a check signal such as an idle validation switch?
Knowing the signal characteristics, you could probe right at the sensor, at the ECU, and in-between, to see if the signal is conforming with the TPS position properly or not, and if the problem is in the wiring, you could narrow down which wire and at what point in the wire the problem exists.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: fuel injectior flutter on race engine

(OP)
Thanks to Hemi for asking a great question. I went back and found the 5 volt reference and the signal out wires switched on the wiring harness. sometimes the obvious is out of reach.

RE: fuel injectior flutter on race engine

Sounds like the ECU was getting a "closed throttle" indication and shutting down the injectors ie "overrun".

je suis charlie

RE: fuel injectior flutter on race engine

So the ecu was seeing 5v from the tps at all times, correct? How was the tps operating normally at some loads and not others if signal out was 5v and reference was actual throttle position?

RE: fuel injectior flutter on race engine

on those days I alwayd heard about bad throttle sensors

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