a little help diagnosing a hard start condition and calling Snap On MT2400 users

[terabyte]

About 1 out of 10 times when starting my 2008 Ford Ranger 2.3 with 46k miles the engine has to turn over a few times before it starts. It normally starts on the first crank.

Its the original battery which I had tested by the auto parts store with one of the nicer Midtronics testers. It tested within one CCA of the spec of the battery.

I do live in south Florida, so batteries don't last here long at all.

This morning I figured I would do a little test.

Battery Voltage is 12.69V
Charging voltage is 14.14V at idle

Its 70 degrees outside. Snap-On MT 2400 says that while cranking the engine over the voltage goes down to 7.32V. Fluke 87 set to record min and max says the voltage goes down to 9.8V. Both read the exact thing with the truck running or off.

I'm guessing that I'm not giving the fuel pump any time to prime and build up pressure is the reason for the occasional hard start (3-5 turns before it starts). What do you guys think?

Secondly can someone intimately familiar with the Snap-On Mt 2400 give me an idea of why its readings are so off from the Fluke when reviewing the low spot of the histogram?

 

[nehog]

Where did you connect the fluke? Odds are you measured in one place, and the Snap-On measures in a different place. Have you cleaned/checked the battery terminals?

 

[HookWorse]

If it's cranking over normally and just not firing, I'd be putting a fuel pressure gauge on it and see if the pressure is bleeding off when shut off. If so, it may take that few seconds to build the pressure back up.

Not sure why the meters would read differently.

 

[MattT]

The difference in readings could be due to the sampling rate on the Fluke. Or the Fluke might use a bit of averaging on the Min value. I wouldn't worry about it too much. Just for peace of mind I'd check both with 1.5v, 3v and 6v if you have them, and 9v batteries just to confirm their low voltage readings.

Another thing were both readings taken on the same crank?

 

[1950ChevySuburban]

Those engines have a crank sensor that can fail partially, leaving a 50-50 shot at the timing being correct.

 

[terabyte]

Where did you connect the fluke? Odds are you measured in one place, and the Snap-On measures in a different place. Have you cleaned/checked the battery terminals?

I connected both directly at the battery. Both connected at the same time and samples taken on the same crank.

If it's cranking over normally and just not firing, I'd be putting a fuel pressure gauge on it and see if the pressure is bleeding off when shut off. If so, it may take that few seconds to build the pressure back up.

Not sure why the meters would read differently.

Yes it cranks over just fine. I will have to dig up my pressure gauge.

The difference in readings could be due to the sampling rate on the Fluke. Or the Fluke might use a bit of averaging on the Min value. I wouldn't worry about it too much. Just for peace of mind I'd check both with 1.5v, 3v and 6v if you have them, and 9v batteries just to confirm their low voltage readings.

Another thing were both readings taken on the same crank?

Hmm that sounds like a good possibility.

Those engines have a crank sensor that can fail partially, leaving a 50-50 shot at the timing being correct.

Will need to look into that.

 

[terabyte]

I went and got a new fuel filter and spark plugs to give the little truck a tune-up. In the 46k miles I have had it I have only changed the oil and put gas in it. Maybe its time I give it a little TLC. I also just put on some ATE rotors and Hawk Blue pads and that made a notable improvement in the slowing down department.

 

[nehog]

I connected both directly at the battery. Both connected at the same time and samples taken on the same crank.

When the SnapOn scan tool reads voltage it is getting it from the ECM, not the battery, so you are seeing what voltage the ECM is getting.

Yes it cranks over just fine. I will have to dig up my pressure gauge.

Hmm that sounds like a good possibility.

Will need to look into that.

If cranking speed is OK, then I'd suggest looking (as others say) at the CPS.

 

[Ohio Auto]

Cycle the key off and on 3 or 4 times every time before you start it. Do it for a couple of weeks. If it solves your problem you probably need a new fuel pump.

 

[terabyte]

When the SnapOn scan tool reads voltage it is getting it from the ECM, not the battery, so you are seeing what voltage the ECM is getting.

If cranking speed is OK, then I'd suggest looking (as others say) at the CPS.

The Mt2400 is a graphing voltmeter. So i was able to hook it up directly to the battery.

Cycle the key off and on 3 or 4 times every time before you start it. Do it for a couple of weeks. If it solves your problem you probably need a new fuel pump.

I'm having a hard time believing it would go out at 46k miles and only 2.5 years old. Is that really likely?

 

[HookWorse]

I'm having a hard time believing it would go out at 46k miles and only 2.5 years old. Is that really likely?

I've seen it before. Don't rule anything out.

 

[Stick]

Its 70 degrees outside. Snap-On MT 2400 says that while cranking the engine over the voltage goes down to 7.32V. Fluke 87 set to record min and max says the voltage goes down to 9.8V. Both read the exact thing with the truck running or off.

...

Secondly can someone intimately familiar with the Snap-On Mt 2400 give me an idea of why its readings are so off from the Fluke when reviewing the low spot of the histogram?

It's probably the "glitch detect" feature of the Vantage. The Fluke 87 is an RMS meter, which averages readings, and the Vantage does too, but the "glitch detect" will graph any signal that happens for 300 microseconds or longer.

I wouldn't sweat it, the midtronics unit said your battery was good, and the Fluke backed it up. I'd be willing to bet if you stepped a bit to the right on the timebase on the vantage, the reading would be fairly close to the Fluke.

 

[terabyte]

I've seen it before. Don't rule anything out.

10-4

It's probably the "glitch detect" feature of the Vantage. The Fluke 87 is an RMS meter, which averages readings, and the Vantage does too, but the "glitch detect" will graph any signal that happens for 300 microseconds or longer.

I wouldn't sweat it, the midtronics unit said your battery was good, and the Fluke backed it up. I'd be willing to bet if you stepped a bit to the right on the timebase on the vantage, the reading would be fairly close to the Fluke.

I was hoping you would chime in. I still remember your post about the lab scope. I'd never heard of this glitch detect so thanks a bunch for the heads up. This is the first time I use the Vantage, I picked it up based on advise of forum members. And yes one step to the right the Vantage is really close to the Fluke.

I figured for $25 it would be a good investment to get a carbon pile load tester so I got this which should be here in the morning. I'm sure it isn't the battery now but who doesn't need mode tools...http://www.amazon.com/gp/product/B000AMBOI0/?tag=atomicindus08-20

 

[dansmurf]

My last 2 Focus had the 2.3L and both would do as you described. There was a TSB to reflash the PCM for the problem. I reflashed the PCM in my first one and it only fixed it for a while then the problem came back. It is a little annoying but don't hurt anything so I haven't even bothered to have my newest focus reflashed.

 

[MattT]

The Fluke 87 is an RMS meter

RMS is Root Mean Squared AC voltage and doesn't have anything to do with DC AFAIK.

 

[MrMark]

RMS is Root Mean Squared AC voltage and doesn't have anything to do with DC AFAIK.

You are right.
RMS is a way of expressing an AC signal as a functional equivalent DC signal.

I'm a little confused on the Vantage though, having never seen one. Why is it connected to the battery if it is a scanner? Is that how it gets its power? But it must be connected to the OBDII connector under the dash, no?

That's not to say that the vantage doesn't do some averaging of its DC readings, a wholly different concept than RMS. Would need to check its sample rate and its timebase.

How fast can the vantage acquire data?

How many data points can it capture?

Where exactly does the vantage fit in the hierarchy of scanners. Is it simply a scanner with an LCD so a limited graph can be displayed instantly?

Inquiring minds want to know if it is worth ditching my Autoxray 4000 for an Ebay vantage?

For comparision, I can capture 14 seconds worth of up to 20 PID's. My fastest sample rate is .5 sec. So, for each PID I can capture 29 data points.

 

[Stick]

RMS is Root Mean Squared AC voltage and doesn't have anything to do with DC AFAIK.

If measuring a constant DC voltage, sure. But he's trying to see how low the voltage swings on starter engagement. If you were to look at it as a waveform it swings low until the starter motor starts turning, then back up (but still low) as the starter turns the motor. It will also swing with the increased current demand from the compression stroke of each cylinder.

From http://www.kpsec.freeuk.com/acdc.htm -

AC voltmeters and ammeters show the RMS value of the voltage or current. DC meters also show the RMS value when connected to varying DC providing the DC is varying quickly, if the frequency is less than about 10Hz you will see the meter reading fluctuating instead.

The vantage is just set up so that it graphs the swing at it's lowest point instead of averaging it out.

 

[Stick]

You are right.
RMS is a way of expressing an AC signal as a functional equivalent DC signal.

Unless the DC varies quick enough to act like an A/C signal. Lots of automotive sensors work that way. Often you can get a bit more resolution on a DSO by using A/C coupling on the signal, but that doesn't change the fact that it's still essentially a DC signal.

I'm a little confused on the Vantage though, having never seen one. Why is it connected to the battery if it is a scanner? Is that how it gets its power? But it must be connected to the OBDII connector under the dash, no?

The MT2400 Vantage is a graphing multimeter, not a scanner. It is essentially a DSO without a super fast timebase. I think the quickest you can set it to is 5ms or so on the waveform viewer and 200ms or so on the meter portion of the unit.

 

[MrMark]

I'd have to read the Fluke 87 specs to see what it does with time varying DC signals.

 

[Stick]

I'd have to read the Fluke 87 specs to see what it does with time varying DC signals.

I would imagine it averages them if they are fast enough, otherwise their meter that is targeted at automotive use (the 88-V) would be an RMS meter as well.

 

[MrMark]

I would imagine it averages them if they are fast enough, otherwise their meter that is targeted at automotive use (the 88-V) would be an RMS meter as well.

Very interesting . . .

 

[MattT]

AC voltmeters and ammeters show the RMS value of the voltage or current. DC meters also show the RMS value when connected to varying DC providing the DC is varying quickly, if the frequency is less than about 10Hz you will see the meter reading fluctuating instead.

The lower end meters use averaging for AC. It's only the higher end meters that measure true RMS. Good point that a, true, RMS meter might give squirrely readings on a variable DC signal and the same could be said for an averaging meter. I guess it all depends on how a meter is "programmed" to act on the DC scale.

 

[Stick]

The lower end meters use averaging for AC. It's only the higher end meters that measure true RMS. Good point that a, true, RMS meter might give squirrely readings on a variable DC signal and the same could be said for an averaging meter. I guess it all depends on how a meter is "programmed" to act on the DC scale.

Not to mention if you spend any time using the AC scale to measure signals with a significant DC bias. I know GM uses RMS values for measurements, while other manufacturers use averaging. Not a huge difference in measurements at automotive voltages, but it is there.

 

[MrMark]

Stick, while we've got you, what is the max voltage drop you like to see on what should be a dead short (e.g., ground connection) before you declare it suspect. I'm guessing 0.3V and higher raises flags.

 

[Stick]

Stick, while we've got you, what is the max voltage drop you like to see on what should be a dead short (e.g., ground connection) before you declare it suspect. I'm guessing 0.3V and higher raises flags.

General rule of thumb for voltage drop is no more than 2% of system voltage. On a 12V system that runs at 13.8V, you wouldn't want more than .276V or so (which is fairly close to the .3 that you mention), and even then that is pushing acceptable limits.

 

[1950ChevySuburban]

How's the Ranger coming along?

 

[terabyte]

rear tyres were gone! so...

I had been wanting these wheels ever since I got the truck...
and I love how it came out.

i found this TSB...
TSB 08-17-6

09/01/08

2.3L ENGINE - INTERMITTENT LONG CRANK
FORD:
2007-2008 Ranger

ISSUE
Some 2007-2008 Ranger vehicles equipped with a 2.3L engine may exhibit an intermittent long crank. This condition can be created if some of the necessary spark events are missed during engine start. This will not create any other diagnostic trouble codes (DTCs) or drivability issues, and is only evident during engine cranking.

ACTION
Reprogram the powertrain control module (PCM) to the latest calibration using IDS release 56.6 and higher. This new calibration is not included in the VCM 2008.7 DVD. Calibration files may also be obtained at the website.

and since it says... This will not create any other diagnostic trouble codes (DTCs) or drivability issues, and is only evident during engine cranking.


I'm not going to really worry about it.

 

[MattT]

and since it says... This will not create any other diagnostic trouble codes (DTCs) or drivability issues, and is only evident during engine cranking.


I'm not going to really worry about it.

It'll be increasing wear on your starter and I doubt it's good for your battery either..............