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Old 2nd September 2012, 19:42   #1
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Default Zen: Injector pulse width

Hi all

I use a MPFI zen.My car is giving very poor mileage(<10km/litre)
Im trying to trouble shoot the problem.

My recent finding is, the injector pulse width is 2.7 milli secs @ 800rpm.
Is this reading correct?

2.7 millisecs @ 800 rpm means a duty cycle of more than 100%.

2.7 * 400(injector fired once per 2 revolutions) = 1080 milli secs
is this calculation right?

i would like to know if this reading 2.7 millisecs is right or should it be less.

Thanks in advance
T1000
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Old 3rd September 2012, 01:26   #2
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Default Re: Zen: Injector pulse width

Hi T1000,

Can I ask how you could know your injector pulse width? I would also know that in my car!

Out of what little I know, for a specific rpm, the injector pulse width should be constant, and not varying.

As for your low FE, please check your O2 sensor, if you feel the pulse width is more.

Last edited by dhanushs : 3rd September 2012 at 01:28.
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Old 3rd September 2012, 08:48   #3
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by dhanushs View Post
Hi T1000,

Can I ask how you could know your injector pulse width? I would also know that in my car!

Out of what little I know, for a specific rpm, the injector pulse width should be constant, and not varying.

As for your low FE, please check your O2 sensor, if you feel the pulse width is more.
Hi dhanush,
I read it using the maruti scanner tool in a workshop.

yes. the pulse width is constant at idling @ 800rpm.

O2 sensor reading in the scanner is 0.365

Thanks
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Old 3rd September 2012, 13:08   #4
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by T1000 View Post
Hi all

I use a MPFI zen.My car is giving very poor mileage(<10km/litre)
Im trying to trouble shoot the problem.

My recent finding is, the injector pulse width is 2.7 milli secs @ 800rpm.
Is this reading correct?

2.7 millisecs @ 800 rpm means a duty cycle of more than 100%.

2.7 * 400(injector fired once per 2 revolutions) = 1080 milli secs
is this calculation right?

i would like to know if this reading 2.7 millisecs is right or should it be less.

Thanks in advance
T1000
You have all your calculations mixed up. Let's talk about a single cylinder out of the 4.

800 rpm = each cylinder (out of 4) having an intake stroke 200 times a minute. Let's divide that by 60 to find out how many of them a second. 3.33. Or 1 intake stroke takes about 0.3 seconds, which is 300 milliseconds. And the injection lasts 2.xx milliseconds. Nowhere near the 100% duty cycle you're claiming. 100% duty cycle is when the injector is spraying continuously, regardless of the state of the valves (open/closed), or the current stroke (intake, compression, combustion, exhaust).

Last edited by pranavt : 3rd September 2012 at 13:10.
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Old 3rd September 2012, 13:19   #5
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by pranavt View Post
You have all your calculations mixed up. Let's talk about a single cylinder out of the 4.

800 rpm = each cylinder (out of 4) having an intake stroke 200 times a minute. Let's divide that by 60 to find out how many of them a second. 3.33. Or 1 intake stroke takes about 0.3 seconds, which is 300 milliseconds. And the injection lasts 2.xx milliseconds. Nowhere near the 100% duty cycle you're claiming. 100% duty cycle is when the injector is spraying continuously, regardless of the state of the valves (open/closed), or the current stroke (intake, compression, combustion, exhaust).
Thanks, i got the information.
http://injector-rehab.com/shop/idc.html

a more complex calculation can be found here
http://www.dainst.com/info/programs/...c/pw_calc.html

But can you tell me, if 2.67milli secs @ 800 rpm is a correct value for a zen?
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Old 3rd September 2012, 15:03   #6
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by T1000 View Post
But can you tell me, if 2.67milli secs @ 800 rpm is a correct value for a zen?
Some 'googling' tells me that typical injector pulse width @idling is between 2.5 - 3.5 ms.

May be pranav or other experts can be more specific.
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Old 3rd September 2012, 16:15   #7
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by dhanushs View Post
Some 'googling' tells me that typical injector pulse width @idling is between 2.5 - 3.5 ms.

May be pranav or other experts can be more specific.
Hi dhanush, thanks for taking the effort, i agree with you , but i also came across few sites which talks abt 1.5ms.

http://www.rx7club.com/wolf-3d-125/i...widths-616740/
http://www.rx7club.com/single-turbo-...s-idle-800239/

i was just wondering what could be the ideal value for a zen?
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Old 3rd September 2012, 17:35   #8
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Default Re: Zen: Injector pulse width

If your car is giving low mileage, there are a myriad of things that can go wrong. It has nothing to do with the pulsewidth. Even if the injectors were stuck open, the reported pulsewidth would be as per the ECU maps.

You need to look elsewhere for a cause.
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Old 3rd September 2012, 17:47   #9
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Default Re: Zen: Injector pulse width

Can you not check the injector pulse width on another MPFI Zen which is running OK?
I think that will help you confirm if this has anything to do with the poor FE at all.
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Old 3rd September 2012, 20:26   #10
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by T1000 View Post
My recent finding is, the injector pulse width is 2.7 milli secs @ 800rpm.
Hi,
Lots of comments to your post (including the calculations), but I'm more interested in knowing how measured. With such definiteness.

Regards
Sutripta

PS: - Should have read the whole thread first before posting. Disregard post.

Last edited by Sutripta : 3rd September 2012 at 20:37.
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Old 3rd September 2012, 20:48   #11
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by Sutripta View Post
Hi,
Lots of comments to your post (including the calculations), but I'm more interested in knowing how measured. With such definiteness.

Regards
Sutripta
Hi Sutripta...
First, let me give you the background
im trying to solve this mileage problem for months with no help from MASS.i had gone to 3 MASS. none interested in troubleshooting, they have changed all the parts that they could. so im trying to troubleshoot myself.

How i measured?
There is a handheld device known as scanner or On-board Diagnosis tool.
It looks like a handheld credit-card POS terminal.

This device gives real time information about various sensors in the car like
temperature, pressure, amount of fuel injected, throttle position, O2 sensor values, rpm, timing advance..etc.

Normally the mechanics don;t use it, i had to request them many times to take it out of their cupboard and check the settings.(It was neatly packed and looked brand new :-) ).

One of the parameter is fuel injector pulse width, It tells you how long the injector is kept open to spray fuel
It was 2.67 milli secs when idling, when you open the throttle, the time increases proportionately, so more fuel is injected.

I read in some websites that the pulse width can range from 1.5 milli secs to 20 ms or so.

so i want to check if the value 2.67 is correct or not.

It was interesting to watch the values changing with rpm and temperature.
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Old 3rd September 2012, 20:53   #12
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by T1000 View Post
Hi all

I use a MPFI zen.My car is giving very poor mileage(<10km/litre)
Im trying to trouble shoot the problem.

My recent finding is, the injector pulse width is 2.7 milli secs @ 800rpm.
Is this reading correct?

2.7 millisecs @ 800 rpm means a duty cycle of more than 100%.

2.7 * 400(injector fired once per 2 revolutions) = 1080 milli secs
is this calculation right?

i would like to know if this reading 2.7 millisecs is right or should it be less.

Thanks in advance
T1000
If you're looking to improve your mileage, you're barking up the wrong tree with pulse width calculations. There are several usual causes for low mileage - you'll find your answer there.
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Old 3rd September 2012, 21:01   #13
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Default

Quote:
Originally Posted by pranavt View Post
If your car is giving low mileage, there are a myriad of things that can go wrong. It has nothing to do with the pulsewidth. Even if the injectors were stuck open, the reported pulsewidth would be as per the ECU maps.

You need to look elsewhere for a cause.
Pravnav, thanks for dropping in.
I used to get good mileage earlier like 23km/hr in the highway and about 17km in navimumbai traffic , which is good for a zen.

Well, the following things were checked till now and ruled out as a reason.
1. IAC value changed.(things got better after this, but the problem cropped up again)

2. Suspected Vacuum leak(idling used to be very high)
2a. brake vacuum pipe changed.
2b. all vacuum hoses checked.
2c. All packing in inlet manifold changed
2d. Inlet manifold gasket changed

3. Distributor cap changed
4. Spark plugs changed
5. Brakes are not dragging
6. Clutch is in good condition

7. Engine tune up done
7a.tappet settings checked
7b. timing adjusted

8. Injector cleaned.
9. TP Sensor was adjusted, it was at 0.9V..changed to 0.7V when the throttle is in fully closed position.
10. air filter changed.

The latest news is, i found the pulse width in the scanner.
Im not sure if it has any role to play.

Quote:
Originally Posted by anandpadhye View Post
Can you not check the injector pulse width on another MPFI Zen which is running OK?
I think that will help you confirm if this has anything to do with the poor FE at all.
Hi Anand, Thats the idea of posting it here and ask for expert opinion.

I got the service manual from the forum, it was very useful in digging out more information about the engine.

Last edited by Rehaan : 3rd September 2012 at 22:27. Reason: Merging consecutive posts
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Old 3rd September 2012, 21:17   #14
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Default Re: Zen: Injector pulse width

Quote:
Originally Posted by T1000 View Post
Hi Sutripta...
First, let me give you the background
im trying to solve this mileage problem for months with no help from MASS.i had gone to 3 MASS. none interested in troubleshooting, they have changed all the parts that they could. so im trying to troubleshoot myself.
As others have mentioned, if poor fuel economy is the problem, go by traditional diagnosis flowcharts. First eliminate all the quick/ easy/ cheap to check/ test jobs first. Then the more esoteric. Injector PW I don't think figures in any standard procedure.

What economy were you getting before, and what are you getting now? Was the change sudden?

Regards
Sutripta

PS. High idling speed: persists? Or if tackled, how?

Last edited by Sutripta : 3rd September 2012 at 21:20.
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Old 3rd September 2012, 21:22   #15
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Default Re: Zen: Injector pulse width

Check resistance offered by various moving parts like the Power steering pump, AC compressor, water pump, etc.

Get the wheels checked for any unnecessary binding or friction.
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