No Injector Pulse GM TBI

dayman · Post by **dayman** » Sun Feb 02, 2014 12:13 pm

I have installed a GM TBI throttle body on my Ford 250 6 cyl. Head is built to mount 2 barrel carb. When I power up the MegaSquirt II 3.0 ECM, I do not get a initial pulse of fuel from the injectors and the engine does not start. I am attempting a fuel only install at this time.

I am new to MegaSquirt and I have attempted to read most of the Mega manual, but have not been able to solve the problem. I have attached my latest msq.
Any help would be appreciated.

kjones6039 · Post by **kjones6039** » Sun Feb 02, 2014 2:40 pm

Nothing jumps out at me in your msq.

A couple of questions to though:

Does the fuel pump prime as described in the manual?
If it does, have you checked for adequate fuel pressure for those injectors?
Speaking of injectors.... I see in your msq, you are using PWM to run them. Are you certain that they are in fact low impedance?

Let's see what the guru's think.

Ken

dayman · Post by **dayman** » Sun Feb 02, 2014 7:10 pm

The injectors do not prime when the ignition is on RUN. I forgot to mention that.

I do have good fuel pressure 40 lbs + and it is stable when trying to start engine. I am using a GM throttle body with two injectors and from what I have read they need about 15 lbs pressure to function and the injectors are low impedance.

It is probably something simple, but with my inexperience, I cannot see it. Also for got to mention I am using the DY relay board and I bought all the sensors from them. I will post a datalog Monday afternoon after I get in from work. Maybe it will show something.

Thanks for the feedback.

trakkies · Post by **trakkies** » Mon Feb 03, 2014 12:51 am

Does the injector LED show the pulse at switch on?

dayman · Post by **dayman** » Mon Feb 03, 2014 5:03 am

I haven't noticed. I will check and get back later today (Monday) after I get home from work. I know one of the LED's flash when I am trying to start the engine.

I will test and be more specific later today.

Thanks

trakkies · Post by **trakkies** » Mon Feb 03, 2014 7:50 am

The injector LED is fed from a different port to the actual injection drivers - but what it does show is the system is getting tach pulses and attempting to fire the injectors while cranking. The injector pulse LED is the one closest to the DB9 connector.

Tuner Studio has an injector test mode (under tools) to allow you to test the actual injector drivers, etc. But have you got a stim? The injector LEDs on that are driven from the injector outputs, unlike the one on the MS itself.

dayman · Post by **dayman** » Mon Feb 03, 2014 5:58 pm

I think I may have discovered the problem. When I calibrated the TPS I had a low number of 268. The mega manual says you are in flood clear mode if TPS ADC > 155 and NO fuel will be injected while cranking. My number is way above the 155 limit.

I have tried to recalibrate the TPS, but I cannot adjust the switch to get the number below 155. May have a bad TPS. I will post results when I have the TPS calibrated and within the correct limits.

kjones6039 · Post by **kjones6039** » Mon Feb 03, 2014 7:39 pm

It sounds like you're on the right track!! I have one concern though........

but I cannot adjust the switch to get the number below 155

Is this correct? Are we working with a switch here?

Ken

dayman · Post by **dayman** » Tue Feb 04, 2014 4:33 am

My bad. It is called Throttle Position Sensor -TPS.

Thanks for catching that.

The throttle body I am using came off a 1996 GMC 4.3 Sonoma truck. There is very little movement available to adjust the TPS. I have tried to enlarge the mounting holes to allow more movement, but so far I have only been able to get the TPS ADC to 180. I am still about the limit of Flood Clear Mode of ADC>155. I am researching now to see what other options I have available.

Thanks

trakkies · Post by **trakkies** » Tue Feb 04, 2014 8:15 am

Don't see how TPS setting would stop the priming pulse?

kjones6039 · Post by **kjones6039** » Tue Feb 04, 2014 11:51 am

trakkies wrote:Don't see how TPS setting would stop the priming pulse?

I agree, although it can certainly cause other fueling issues. Now you've got me curious Dave. I'll test it on my spare box when I get home.....

Ken

trakkies · Post by **trakkies** » Tue Feb 04, 2014 3:35 pm

I suppose the flood clear mode could kill it? Something I'll have to check too. However, that doesn't compute to an LED flashing when cranking.

dayman · Post by **dayman** » Tue Feb 04, 2014 6:10 pm

Raining at my place tonight and car is outside. It will be another day before I have any additional information.

Thanks guys for taking an interest. Really would like to know how the test comes out on your spare box.

Thanks

dayman · Post by **dayman** » Wed Feb 05, 2014 3:02 pm

I have a confession to give. I have solved the problem.

I put the fuel lines on the throttle body wrong. I put the return line on the inlet side and the pressure line from the tank on the outlet side. Switched the lines and the engine started up instantly.

I apologize for wasting your time. Thanks for your willingness to help. It is appreciated.

kjones6039 · Post by **kjones6039** » Wed Feb 05, 2014 4:12 pm

NP..... It actually gives me comfort, to know that I am not alone when those things happen to me!

Glad to see you got it solved!

Ken

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No Injector Pulse GM TBI

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