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I’ve repeatedly read that it does absolutely nothing, but I have learned that is not true. My 2002 excursion has always been a bit slow to start, probably due to the high mileage on the injectors. If I press the accelerator while cranking it fires up noticeably quicker, hot or cold.
When it sits a long time and the batteries get low it becomes even more noticeable. I’ve had a couple occasions where I didn’t think it was going to start before running out of battery, pressed the throttle and she fired right up.
They did away with that necessity decades ago when electronic control came on the scene. Gas or diesel, doesn't matter. If you have to step on it while cranking, there's an issue that needs resolving.
They did away with that necessity decades ago when electronic control came on the scene. Gas or diesel, doesn't matter. If you have to step on it while cranking, there's an issue that needs resolving.
I have no doubt that there is an issue, probably my injectors. My only point was that it definitely makes a difference despite everything I read saying that it won’t do anything at all.
I read a few other threads where people stated that it had to be a placebo effect because they knew for a fact that it can’t change anything and I believed it. My buddy started my truck after it had been parked a while. The batteries were dropping off and he thought it wasn’t going to start, then he pressed the throttle and it fired up. I was sure that he was wrong till I tried it, sure enough, it makes a big difference.
Ok we need data to solve this one. All the pedal does is send a signal to the PCM saying you want to to faster. Some the question is does the PCM respond at all while the engine is cranking. So what PID do we monitor to get the answer, pulse width?
My thoughts went to your oil fuel pump, since I just replaced mine. Maybe pushing the pedal gives it more fuel pressure ??? Just my thoughts...
Going to look at a 2003 Excursion tomorrow I might buy, unless my spousal unit beats me to death if I say Yes to the guy....
The fuel pressure is mechanically controlled so that won’t change. I’m guessing the accelerator while cranking is adding injector pulse width and/or injection pressure. I’ll try to remember to check those next time I am starting it.
Another possibility hit my mind yesterday: if my idle validation switch isn’t working, maybe that could cause the slow starts and pressing the accelerator is compensating for it.
The fuel pressure is mechanically controlled so that won’t change. I’m guessing the accelerator while cranking is adding injector pulse width and/or injection pressure. I’ll try to remember to check those next time I am starting it.
Another possibility hit my mind yesterday: if my idle validation switch isn’t working, maybe that could cause the slow starts and pressing the accelerator is compensating for it.
that switch might be it
My IDI would start faster (less cranking) at 1/8 throttle than set to idle
maybe for you,
but not for my Vibe, or my Suburban, nor on my '02 7.3L
I should have added:
" the delay after the WTS light went off, to engine start was "the same",
but the reaction after it started was Violent,
it ramped up to 3,000 RPM so fast, I couldn't get my foot off the throttle quick enough.
The fuel pressure is mechanically controlled so that won’t change. I’m guessing the accelerator while cranking is adding injector pulse width and/or injection pressure. I’ll try to remember to check those next time I am starting it.
Another possibility hit my mind yesterday: if my idle validation switch isn’t working, maybe that could cause the slow starts and pressing the accelerator is compensating for it.
Idle validation switch is a simple on or off sensor. The equivalent of a momentary push button. If it was reporting incorrectly pushing the pedal wouldn't change what it's reporting. I still say data is what we need.
Take this data with a grain of salt - I was curious and gave this a try this evening. Just one test at 20% APP, and one at idle (13% APP). I should do a few more to see how variable this experiment is.
Moved the go pedal to about 20% first, watching APP on FORScan, then cranking the cold engine. As expected, RPM exceeds idle for just a bit until I let off. I used time from start of crank to reaching 700 RPM as a benchmark for a running engine. Results below:
Waited about an hour, and tried this again with the go pedal at idle. There was a measurable difference in start time. Note the max values. It is interesting that ICP peaks about 50psi less, and FUELPW peaks at almost 2ms more than the 20% APP test. Not sure why peak PW would be higher for an idle start.
Here is a cold start chart from January - outside temps much colder at 36 degrees F. RPM at idle is higher than 700 on cold start, as commanded by the PCM. IPR is higher, ICP is lower, and PW is much higher than the previous charts. Time to 700 RPM is same as having the pedal down a bit.
Sorry about the different horizontal scales - the charting tool autoscales depending on how many data points come in.
So what to make of this? The data seems to say that giving a bit of pedal results in a quicker start.
What is not intuitive is that the first chart with the pedal pressed a bit should have had a larger FUELPW, similar to the January cold start, but it does not. I will do a couple more tests to verify this data tomorrow.
