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Thread: It cranks forever and then backfires. Why?

  1. #1
    On a roll Al_C's Avatar
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    It cranks forever and then backfires. Why?

    Second generation Coyote. When cold, it will crank and crank and crank. 20 seconds +. Then as it catches, it will backfire and spew a fair amount of smoke. I mentioned this little challenge a few weeks ago in my go-kart thread. At that time, I thought my fuel pressure was too low. Not so. I checked the pressure while the engine was running and it was over 80 psi. I lowered it to between 55 and 60. (spec is 55, I believe) No difference.

    This is a relatively new problem. What changed? I didn’t have the vacuum lines or PCV connected before. They are now connected via inserts into the air intake elbow. I also have new fuel lines (3/8 feed vs. 5/16 originally). I can’t see how a vacuum line or a crankcase ventilation line would have an effect, unless there is something screwy going between those plug-ins and the MAF sensor.

    So, in my (limited experience) mind, these are the possible causes:

    1. Lack of fuel / fuel pressure. Toward that end, I checked the pressure (see above). I have tried cycling the fuel pump two or three times prior to engaging the starter. No difference.
    2. MAF sensor issues. Haven’t done anything to it, except install the PCV and vacuum connections on the same elbow. I haven’t heard of others having this problem and I know I’m not the only one to install these in this spot.
    3. Clogged injectors or clogged fuel filter. However, these are all new parts. If the injectors were clogged, they wouldn’t smooth out and run – I have to believe it wouldn’t even start. Upon start, idle is 1200 rpm and then it settles down to 1000 and lowers a bit more once the fan kicks in.
    4. When it does catch, I get a backfire – usually on the passenger side – and a fair of smoke. Could it be too rich a mixture? That would point to the MAF, no?

    I’m considering unplugging the MAF sensor and giving it a whirl this evening. Any other thoughts, ideas, suggestions, or humorous remarks?
    Mk IV Roadster - #8650 - delivered 7-17-2015 - first start 7-28-2018 - first go-kart 10-13-2018 - licensed and on the road 9-9-19: body/paint completed 3-17-2020.
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  2. #2
    Straversi's Avatar
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    Double check the MAF sensor. I had inadvertently flipped the pipe section containing the MAF when I was installing a different air filter. It cranked and sputtered like you describe.
    -Steve
    Mk IV #8901 - Complete kit, Coyote, TKO-600, IRS. Ordered 5/23/16, Delivered 7/14/16, First Start 8/13/17, First Go-Kart 10/22/17, Registered and Completed 10/18/18. Build Thread: http://thefactoryfiveforum.com/showt...V-Coyote-Build Graduation Thread: https://thefactoryfiveforum.com/show...-Roadster-8901

  3. #3
    David aka Ducky2009 Ducky2009's Avatar
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    Al, When you changed your fuel line(s), did you eliminate the return line? If I remember correctly, you have a gen 2 Coyote. They don't run right without a return line.
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  4. #4
    On a roll Al_C's Avatar
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    My return line is also 3/8. I'm walking out to the garage now to see if I can do something with the MAF sensor. As they used to say in the news business, "film at eleven".
    Mk IV Roadster - #8650 - delivered 7-17-2015 - first start 7-28-2018 - first go-kart 10-13-2018 - licensed and on the road 9-9-19: body/paint completed 3-17-2020.
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  5. #5
    On a roll Al_C's Avatar
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    It's not 11 yet, but so what. Here's the MAF:



    It only goes in one way. I am positive I put the piece in correctly. I get what Steve S. said, but I am certain (who knows, maybe I will eat my words...) it is in correctly.

    So, I disconnected the plug and turned the engine over. Started pretty quickly. No backfires. It wasn't happy though, it stumbled and needed throttle to keep it going. Shut it down and plugged the sensor back in. Started right up (again), but was still not very happy. No backfires though. Finally, it evened out at 1000 rpm, then dropped to 800. went back up to 1000 and stayed there. Once it stabilizes itself, she runs smoothly.

    Not sure this provides much input for you guys, but I'm certainly open to your ideas. I can't imagine that the sensor is bad already. It only has about 45 minutes of use...
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  6. #6
    Senior Member Jdav's Avatar
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    It looks like it is on the rear side of the tube. Mine is on the front side of the tube. I dont know why, but i seem to remember it was important that it was that direction
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  7. #7
    BadAsp427's Avatar
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    The air must pass the MAF in the correct direction. I would say that the MAF (complete tube assembly) needs to be turned 180* so that it can read the amount of air going past it. Think of it trying to take your medicine with the spoon upside down. (I don't know where that analogy came from but I hope it helps)

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  8. #8
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    If that is a Spectre MAF tube, it will allow you to mount the sensor in the wrong direction. My tube had an arrow indicating air flow. When I tried to mount the sensor the holes were wrong. I had put the black plastic adapter on wrong. Use the other set of holes and all fits correctly.
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  9. #9
    Senior Member wareaglescott's Avatar
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    AL have you called the Ford Performance tech support line? What did they say. There is some great knowledge to be had from the forum members obviously but those guys really know their stuff. IF you have not spoken with them yet I would recommend it.
    MK4 #8900 - complete kit - Coyote, TKO600, IRS - Delivered 6/28/16 First Start 10/6/16 Go cart - 10/16/16 Build completed - 4/26/17 - 302 days to build my 302 CI Coyote Cobra - Registered and street legal 5/17/17
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  10. #10
    On a roll Al_C's Avatar
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    The good news is that I don't have to eat my words. Check out this photo:



    The MAF sensor is indeed installed correctly. (I was beginning to think I had it in backwards...) Next step: take Scott's advice and call Ford. Thanks for the reminder, Scott! We'll get this figured out soon.
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  11. #11
    Senior Member edwardb's Avatar
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    I assume that last picture of the MAF sensor is with the air filter removed so looking in the direction air would move. If so, yes that's the proper orientation. It is generally recommended the MAF sensor be on the outside of the airflow curve, e.g. on the front of the tube in this case versus on the back. Don't know that this would case the symptoms you describe, but is the recommendation. Unplugging the MAF sensor will either result in a no start or a start and then immediate stop. They system just won't work without it and the PCM will shut things down. If there's something wrong only on one bank and not the other (e.g. the backfire you mention) I would vote it's not from MAF issues. Maybe the O2 sensor on that side. Have you checked for any DTC's (e.g. read codes from the ODB2 port) or your MIL lit? Finally, regarding setting the fuel pressure regulator, it's supposed to be 55 psi. Normally set with only the fuel pump running. But since the Gen 2 only runs the fuel pump briefly, you have to have a helper and see where it peaks while the key is repeatedly cycled. Not the best. Better is to check it with the engine running but with the vacuum reference line removed. If you're setting it while running and the vacuum line connected, no guarantee it's right.
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  12. #12
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    Edwardb, shut down with no maf? At least Some of the old pcm's have a fuel table for defective maf, i would have thought the coyotes would also??? WOW!

    Al_C, it ran then does not after you hooked up vacuum lines, if you are pulling air or loosing air after the maf, it cant have the correct air to fuel. I would think to check all the lines, and try going back to when it ran, then add back till you narrow it down.

    Also, if you had it at 80 psi, you were pushing alot more fuel and could have fouled plugs or O2's.

    It would be nice to have a tuning program to plug into it and see what its doing (i have no idea on coyote options)

    Good luck!
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  13. #13
    On a roll Al_C's Avatar
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    Edwardb - thanks for your input. No codes on the OBD scanner. It did run with the MAF sensor unplugged. Good idea about checking fuel pressure with just the pump running. I'll check that.

    I'm going to call Ford today and see what they have to say.
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  14. #14
    Senior Member edwardb's Avatar
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    Quote Originally Posted by Just puttering View Post
    Edwardb, shut down with no maf? At least Some of the old pcm's have a fuel table for defective maf, i would have thought the coyotes would also??? WOW!
    Quote Originally Posted by Al_C View Post
    Edwardb - thanks for your input. No codes on the OBD scanner. It did run with the MAF sensor unplugged. Good idea about checking fuel pressure with just the pump running. I'll check that.
    Hmm. I seemed to remember testing that when I was trying to see if my MIL worked. Unplugged the MAF sensor and it neither started or threw a code. But then that was a couple years ago. So maybe I'm not remembering it exactly. I can say for sure if it's not getting an airflow reading the engine will start but then immediately stop. I have the pictures to prove it. https://thefactoryfiveforum.com/show...-Ride-of-Shame.

    Good luck getting it sorted out. Hopefully the Ford guys can give you some helpful suggestions.
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  15. #15
    On a roll Al_C's Avatar
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    I thought this was going to be quick, easy, and painless. I figured I'd post the symptoms, somebody would say "yup, that happened to me and this is how I got past it". For whatever reason, that didn’t happen. No matter. Perhaps I led people down the wrong path by originally suspecting the MAF sensor as the culprit. In any event, I'm out of fix-it mode and into learning mode.

    I just got off the phone with Ford Tech Support. His first question was "who modified your PCM?" "Well, nobody", I said. "There's your problem," he replied. He indicated that because the air intake is different, the programming needs to be modified to adjust for that. I don't remember seeing anything about this in the FFR instructions. Perhaps I just didn't read it carefully, or perhaps the Ford guy is conservative on this topic. You be the judge. I don’t remember ever seeing any “ford racing” instructions for fuel pressure, air intake, etc. The only instructions I have (or read for that matter) are the controls pack instructions.

    We talked about fuel pressure, too. His instructions:
    1. Fuel pressure at idle with vacuum not connected should be 55.
    2. When vacuum is all connected, it should be 30PSI.
    3. His opinion was that modifying the PCM is "mandatory". "We see this all the time," he said. "Do it now or you'll have bigger problems down the road." Seems like a rather dire prediction. Maybe he's right, maybe not. Maybe you'll have a different opinion.
    He also suggested I re-read the instructions. Hmmm – anybody know where I can find them? Other than the FFR instructions or the Controls Pack instructions, I’m at a loss.

    So, now we'll pivot this whole thread to a related but somewhat different question:

    If you have a coyote, a) did you modify your PCM? If you did, what software did you use? or who did the tune/modification for you?

    Right now, it would appear that I need to disconnect ALL of the vacuum lines and re-do the fuel pressure measurement. Then see if I can find software that will take care of the air/fuel end of the PCM program that will work for a roadster. As always, your input is welcomed!
    Mk IV Roadster - #8650 - delivered 7-17-2015 - first start 7-28-2018 - first go-kart 10-13-2018 - licensed and on the road 9-9-19: body/paint completed 3-17-2020.
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  16. #16
    Senior Member edwardb's Avatar
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    What you received is the standard Ford Performance party line on the Coyote crate motor. I was told the same thing back when I started installing the Gen 2 Coyote in #8674. "If you don't use the standard OE air box you'll have issues with how it runs and even potentially damage the engine." They asked if I could use the standard air box even if it meant taping it to the fender or something. Seriously. I challenged that over several phone calls and they finally agreed that if I used the stock diameter intake (which the Spectre setup recommended by FF is) and set up everything else per the instructions it would be "OK" and the PCM would learn my setup. First start was perfect and it ran fine through the balance of the build. I drove it with the stock setup for just over 1,000 miles and it ran OK. I also had a streaming ODB scanner that I used to watch how it was running, specifically the A/F ratio which they warned could be lean and that's when I could damage the engine. It always was fine and nothing ever was a problem. When I was doing my build, I researched and talked to a number of other builders who also successfully ran the stock tune. It does work OK.

    I did end up doing a custom tune with Lund Racing and it improved how it run significantly. Mainly at the lower RPM's where it was just "happier." But no way did I have any kind of issues like you're describing running with only the stock tune. So bottom line, I don't agree with what they told you. I also don't agree with the 30 psi rating for the regulator with the vacuum attached and engine running. I've never seen that. Depends very much on what vacuum the engine is pulling at the time. 55 psi without the vacuum line attached and you're done. As I think I mentioned before, if not here but in other threads, the custom tuners I'm aware of specifically say to run the engine without the vacuum reference line on the regulator. Just let it vent to atmosphere. I've run mine extensively with and without the vacuum reference, and to be honest could never tell the difference.

    Ford Performance always has the latest version of their instructions on their website: https://performanceparts.ford.com/do...-6017-504V.pdf. As does Factory Five: https://www.factoryfive.com/wp-conte...ster-rev-Z.pdf. Those are the only instructions I'm aware of.
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  17. #17
    On a roll Al_C's Avatar
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    Quote Originally Posted by edwardb View Post
    What you received is the standard Ford Performance party line on the Coyote crate motor. I was told the same thing back when I started installing the Gen 2 Coyote in #8674. "If you don't use the standard OE air box you'll have issues with how it runs and even potentially damage the engine." They asked if I could use the standard air box even if it meant taping it to the fender or something. Seriously. I challenged that over several phone calls and they finally agreed that if I used the stock diameter intake (which the Spectre setup recommended by FF is) and set up everything else per the instructions it would be "OK" and the PCM would learn my setup. First start was perfect and it ran fine through the balance of the build. I drove it with the stock setup for just over 1,000 miles and it ran OK. I also had a streaming ODB scanner that I used to watch how it was running, specifically the A/F ratio which they warned could be lean and that's when I could damage the engine. It always was fine and nothing ever was a problem. When I was doing my build, I researched and talked to a number of other builders who also successfully ran the stock tune. It does work OK.

    I did end up doing a custom tune with Lund Performance and it improved how it run significantly. Mainly at the lower RPM's where it was just "happier." But no way did I have any kind of issues like you're describing running with only the stock tune. So bottom line, I don't agree with what they told you. I also don't agree with the 30 psi rating for the regulator with the vacuum attached and engine running. I've never seen that. Depends very much on what vacuum the engine is pulling at the time. 55 psi without the vacuum line attached and you're done. As I think I mentioned before, if not here but in other threads, the custom tuners I'm aware of specifically say to run the engine without the vacuum reference line on the regulator. Just let it vent to atmosphere. I've run mine extensively with and without the vacuum reference, and to be honest could never tell the difference.

    Ford Performance always has the latest version of their instructions on their website: https://performanceparts.ford.com/do...-6017-504V.pdf. As does Factory Five: https://www.factoryfive.com/wp-conte...ster-rev-Z.pdf. Those are the only instructions I'm aware of.
    Thanks, Paul! My vacuum is set up as you had recommended. I'll leave that alone. My fuel pressure is at 55 psi. I'll leave that alone. If I cut a zip tie on the DS head, I can get enough length out of the MAF sensor wire to move the sensor to the front (not that it should make any difference in my mind).

    So, if moving the sensor doesn't work, I'll live with long crank times. Time to move on to the next challenge.
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  18. #18
    Senior Member wareaglescott's Avatar
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    My experience is much the same as Pauls. I drove it just fine for 1000 miles before a tune.
    I suggest you call back and ask for Ray Herron. Maybe he is still there. I dealt with him extensively and we finally figured out I had a bad wiring harness. He is very sharp. Maybe he could give you a fresh perspective.
    MK4 #8900 - complete kit - Coyote, TKO600, IRS - Delivered 6/28/16 First Start 10/6/16 Go cart - 10/16/16 Build completed - 4/26/17 - 302 days to build my 302 CI Coyote Cobra - Registered and street legal 5/17/17
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  19. #19
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    Make sure you allow the fuel pump to run before cranking and it maintains pressure while cranking.
    I do not know what the results would be if your pressure and return lines are reversed on the regulator?
    Are you feeding your ECU or PDB off the starter?
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