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starts but dies at 151F ECT

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I've recently started my 3.5L honda v6 for the first time. The start up goes well, but all of a sudden at 151F ECT the engine abruptly dies. When cranked again, it will start for a moment, then dies as if fuel was cut.

I suspect a vacuum leak, as Lambda is pegged at 1.2 on both banks of o2, with a target of 1.0. Thinking that as the idle compensations decrease with ECT, and the ecu runs on non-compensated tables it can't adjust for a leak. I've searched for any leak with starter fluid, but can only find an extremely small one at an intake runner on one cyl, not a massive one as the AFR suggests. Changing VE while warming to 151 ECT has little effect on the pegged 1.2 lambda. As the ECT approaches 151 lambda decreases slightly to 1.1

Am I way off and missing something simple?

My next thought is to up the idle speed until I can get AFR in line.

Any help is appreciated. infinity file attached.


Attached Files

adding pc logging file

Attached Files

fixed a very small vacuum leak new log file posted.. still dies at 151F ECT

Attached Files

Bump for aundre

What sensors are you using for load? TPS, MAF, MAP?

Have you retained the OEM idle control?

Are your wideband sensors ok and have you calibrated them correctly? It could be they are giving a false lean reading and you're adding far too much fuel. Does the exhaust reek of fuel?

If not, and you truly are lean, is the fuel system able to supply enough fuel? (Pump, lines, injectors) (is the fuel filter flowing or restricted)

Another idea is to delete all of your compensation tables and use your foot as the compensation as you monitor lambda while the engine warms. This may highlight the true cause.

Or, one way out in left field, are there any protection strategies enabled that may be cutting fuel at this ECT or for any other reasons?

These are just a few of the possibilities I can think of. I hope it helps!


I think your problem may be your idle control (IAC valve setup). Your Idle target table Goes down to 900 RPM at 70 degC (from 1000 @ 60degC), and it's 938 when the engine dies -- the idle position has been changing the entire time and when it finally get's to about 29 the engine dies. To me it looks like it might be wired backwards, or the PID values need to be inverted.

I would try disconnecting that while just getting the engine to run.

Also, your VE numbers are really high -- are you sure the correct injectors are configured, and that all the sensors are giving reasonable values?


What sensors are you using for load? TPS, MAF, MAP? --- I am using a stock honda Map sensor, and TPS.

Have you retained the OEM idle control? --- Yes I am using a stock Honda IACV. which I assume is just a solenoid.

BOTH O2 sensors are brand new from AEM, external controllers. Calibrated per the instructions and connected to Lambda 3 and Lambda 4. They are set to reference 3 and 4 and not 1 and 2 in infinity tuner for Lambda FB.

As per your fuel comments.. I'm installing an AEM Fuel pressure sensor to track the fuel system for diagnostics and better fuel control.

I have also reviewed all the protection and none of them show any signs of a cut at 151F.


Seems like you're set-up well.

Also, David had great recommendations with the VE numbers being astronomical and checking the idle solenoid for correct wiring / settings.

Your idle control is working its heart out after start-up to keep the engine at 1100 rpm but, goes to 30% effort after your first drop to 500 rpm, yet it seems your idle target is between 1000 - 900 for that coolant temp.

David and Rotar-wee,

Thank you both for your insight on the IACV trace. And David's observation is correct the VE is way out of a realistic range. We will be stepping through all of the issues one at a time when the car gets back tomorrow. 1. fuel pressure validated, 2. trace IACV wiring 3. swap map sensors to a second used OEM sensor. 4. attempt running without IACV 5. unplug coolant temp sensor and look for different result.

here is a quick update to my work..

1. added Fuel pressure sensor.. no issues.. 43psi at idle no drop off in psi when the car stops at 151F

2. swapped Map sensors (honda stock for honda stock)

Here is the big one..

3. unplugging the ECT sensor keeps the car running. when unplugged the fail safe returns a temp of 32F.. and the car will continue to run.

Now the question is WHY?


Because your idle target table has a change to less than 1000 RPM at the 60-70 degC temperature. If you never let the ECT get to that temp, then it will never change the idle target (or try to move the IACV) -- try setting the idle target to 1100 RPM for all temperatures (since your engine seems to idle at that easily) and see how that works with the ECT connected.


Great reasoning.. I did just that in my early diagnostics.. setting all idle targets to 1200.. same result. I will re-test that one more time.

In the mean time, I have replaced the mazda fuel pump, and stock honda Fuel pressure regulator..

David, and Rotar-wee

The VE issue is solved!!!.. The idiot (that would be me) wired both O2 sensors wrong. O2 tracking with VE now and stable around 65 at idle. The IACV continues to track to a max -50 feedback and a position of 0. I will be tracing the IACV wires tonight to ensure we have 12v, ground and the signal from the AEM C1-3 pin. If that all checks out, I will replace the IACV itself.

Thanks for everyones help! getting closer now..



we have come to the end!!! PROBLEM SOLVED!!!!! WE HAVE IDLE CONTROL!!! AND ECT ABOVE 151F!!

The output assignment was pointing to lowside3 on pin 22 when it needed to point to lowside6 on pin 3. don't ask me why this pin assignment mistake kills the engine at 151.. don't really care at this point.. it works!

Thank you all again for taking the time to look over my logs and offer help!

Good job finding a problem like that!

Awesome job Peter! Believe it or not, figuring all of that out will pay dividends in the future when you have to diagnose a poor running condition on either your, or another's car. Kudos again!

And thank you for following up with all of us on the solution. I for one really appreciate it!

Now go make the little v-6 purr!


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