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F-150 Buck/Jerk at 50-60 mph

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  • F-150 Buck/Jerk at 50-60 mph

    My truck has an ongoing problem that I haven't been able to figure out. Any help from those with experience would be appreciated.

    I have a 2001 F-150, 5.4L Bi-fuel GFI factory installation with 94,000 miles. The truck is in excellent condition for the mileage and starts, idles and runs great on both gasoline and CNG. The truck was previously owned by Southwest Gas in Phoenix, and I bought it last November.

    About three weeks after buying the truck I was driving on the freeway in a heavy rain and started to notice an intermittent jerk, like a hard shift. I could tell something was wrong, so I stopped and switched over to gasoline and it ran perfectly.

    In the days that followed, I determined that the truck ran without problems at speeds under about 40-45 mph (great for in town), but when lightly accelerating at speeds from about 50-65 mph it would buck/jerk. The transmission is not shifting, because I can feel the transmission shift normally and notice the change in rpms, and this buck is something different.

    The buck/jerk happens only when driving on CNG.

    To describe what I am calling a buck/jerk, imagine that you are towing someone with a chain and the chain comes tight after having a little slack in it. I also hear a noticeable "clunk" sound coming from the engine.

    About three weeks later, and after experiencing probably 20 of these clunks, my #3 spark plug ejected. After a lengthy repair of the spark plug threads using the Time-Sert Ford Triton #5553 kit, I replaced all of the coil-on-plugs, spark plugs, seals and o-rings.

    After firing it up, I did a vacuum test and the needle held steady at 18 in/Hg (elev 2,500 ft) and behaved correctly under sudden acceleration, etc. The vacuum did not hold after shutting the engine off (I don't know if it is supposed to).

    I test drove the truck under all conditions and blasted up hills on the freeway at top speed with tons of power and no bucking or hesitation. I was elated! About three days later I felt my first buck.

    Drained the coalescent filter again, and filled the housing with 90% isopropyl alcohol--drove about 50 miles and felt a buck.

    Unsealed the tuning screws and returned them to the neutral position. The driver side screw was turned down at least three full turns fully sealed; that didn't seem right. After checking the high state O2 readings as specified in the manual, the neutral screw settings seemed to be giving good readings. This time I drove the truck for about 100 miles on the freeway before I felt a buck.

    Today I finally received the correct coalescent filter element and I changed that out. When I drive the truck to Salt Lake this weekend, I fully expect to feel a buck and end up driving 80% of the way on gasoline.

    My next step is to either sell it to some unsuspecting fool (I don't know if my conscience will allow that) or install a TechnoCarb system.

    Sorry about the long post, but this has consumed the last 4 months of my life and I had to get it off my chest. Please help if you can.

    Samuel
    2001 F-150 5.4L Bi-fuel
    7700 Extended Cab

  • #2
    Re: F-150 Buck/Jerk at 50-60 mph

    Yesterday I talked with a guy that had the exact same truck as I have, and he had the exact same problem (only his spark plug was yet to blow out). He said that one of the shops that does a lot of work on these trucks told him that the hesitation/misfire wasn't really going to damage the engine, so he just drives through it with the problem happening intermittantly.

    I would be very interested to hear from anyone who has replaced the compuvalve in an F-150 bifuel. Are all hesitation and misfire issues resolved with a new compuvalve? I would hate to shell out the money and have my problem persist.

    Samuel
    2001 F-150 5.4L Bi-fuel
    7700 Extended Cab

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    • #3
      Re: F-150 Buck/Jerk at 50-60 mph

      I have a 1999 f150 bi-fuel and with 93k but does not run on cng and it seems to do the same thing you discribe but without the noisey clank i notice if im at higher speeds and only lightly pressing the gas pedal is when it happen the most , hence I'm not running cng/compuvalve so replacing it may not fix your problem,

      good luck
      Damon

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      • #4
        Re: F-150 Buck/Jerk at 50-60 mph

        Mental note to self, do not buy a bi-fuel truck from Samuel in St.George. Just kidding. I posted this to another thread that it also applied to but I think it fits better here:
        My truck (2001 f150 7700) has the same buck/thump/bang/thud...when switching over from cng to gas. It is more noticeable with higher speeds as others mentioned. My truck also has a jerk at times when at high speed, constant or accelerating, seems a bit random (happens on both fuels but I'm mostly on CNG so happens most then). I suspected the transmission due to an occasional torque converter shudder, and in researching, this shudder appears to be yet another frequent issue with Ford trucks. It sounds like it can be fixed with programming shift points/pressures(?), transmission flush, or a high performance valve upgrade. Do any of you have the tranny shudder at times along with the fuel switching?
        Hope we can get this figured out. The f150 sites have gasoline only guys with this shudder and other tranny issues I mentioned.
        Oh, I forgot, what is and where are the "tuning screws" you mentioned making adjustments to?
        Thanks.
        Last edited by darress; 04-13-2008, 01:07 AM.

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        • #5
          Re: F-150 Buck/Jerk at 50-60 mph

          The tuning screws that I mentioned are on the tuning tee (underneath a sticker that says tearing it voids the warranty). The tuning tee is the rectangular metal box that splits the CNG flow coming from the compuvalve to each side of the engine. The Ford Service Manual explains how to do the "tuning". It involves plotting the O2 sensor values from each bank of the engine.

          I had ruled out the transmission because I have never had the buck/shudder occur while on gasoline, so I thought that it would be a CNG only issue, but if the compuvalve has control over the shift points, then maybe that could have something to do with it.

          On a slightly hopeful note, after putting a new coalescing filter in, I took my truck up a fairly long steep mountain road at 55 - 70 mph today without having the problem occur. The buck/shudder/jerk seems to happen at random intervals however, so I am not too hopeful.

          Please post any research or links that you have to the transmission shudder problem, I would like to look at that.

          Samuel
          2001 F-150 5.4L Bi-fuel
          7700 Extended Cab

          Comment


          • #6
            Re: F-150 Buck/Jerk at 50-60 mph

            Check this out. It should keep you busy reading most of today. I haven't finished going through all if it yet but great info and solutions people have come up with.
            http://f150online.com/forums/archive....php/f-25.html

            Comment


            • #7
              Re: F-150 Buck/Jerk at 50-60 mph

              Well, I don't have a bi-fuel, but a similar truck (1998 F250 dedicated) with 114k miles. I can not report any similar problem with steady state cruising around those noted speeds, but kudos for the complete description of the problem, and methodical troubleshooting steps!

              Tim G.

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              • #8
                Re: F-150 Buck/Jerk at 50-60 mph

                I hate to resurrect an old thread, but my F-150 is doing the buck ~60mph on the freeway or when accelerating at <3000rmp. I am just curious if rothstar identified the bad component and fixed the problem?

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                • #9
                  Re: F-150 Buck/Jerk at 50-60 mph

                  It has been couple of weeks since my original post, and it appears that there is some interest in the topic, so I will give a quick follow-up.

                  The tune-up that I described in my original post made my truck run better, and I think that new coils and spark plugs are a good idea for sure, if for no other reason than to check the torque on your spark plugs so that you don't have one blow out of the head like I did (that was a serious repair).

                  After all of the extensive work that I described in my original post, I finally received the correct coalescent filter replacement element and changed that out, and the truck has not bucked once since. That has been nearly three weeks of buck free $0.63/gal driving, so my anxiety over the issue is diminishing.

                  I cannot absolutely confirm that the issue is completely fixed, because I have not taken any long freeway trips yet, but I will keep you posted.

                  If someone out there is experiencing this problem frequently, I would strongly suggest that you stop driving your truck and resolve the issue, or you have a very good chance of blowing one of your spark plugs through the hood.

                  Really your only other viable option is to sell your truck to me at salvage value.

                  Samuel
                  2001 F-150 5.4L Bi-fuel
                  7700 Extended Cab

                  Comment


                  • #10
                    Re: F-150 Buck/Jerk at 50-60 mph

                    I used an Innova 3130 scanner ($200) that has live data capabilities for O2, fuel trim, rpm, MAF, etc. These cheap scanners don't have graphing capabilities, so I had to invent a trick.

                    I videotaped the live O2 numerical readings displaying on the scanner with my stop watch beside the scanner. Then I just replayed the video in slow motion as I entered the time and corresponding O2 reading into a spreadsheet program. That took care of the plotting, so I had a simultaneous graphical display of the O2 reading from each engine bank.

                    This worked very well for the idle readings, but at 2000 rpms, the O2 voltage was jumping up and down a little bit too quickly for my scanner (these cheap scanners can only display data about once per second) so the results were sketchy.

                    I would like to get a scanner that has the capability of reading all of the PIDs and reading the AFCM error codes from the compuvalve. Does anyone have the AutoEnginuity software? Will it read AFCM codes?

                    Samuel
                    2001 F-150 5.4L Bi-fuel
                    7700 Extended Cab

                    Comment


                    • #11
                      Re: F-150 Buck/Jerk at 50-60 mph

                      Does your scanner have freeze frame capability? That's where when it senses a problem, and a thrown code, it will show exactly what engine was doing at time.
                      Also, I've seen where the seals on the injectors dry out and can can cause misfire, but I don't know how erratic that would be.
                      Max

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                      • #12
                        Re: F-150 Buck/Jerk at 50-60 mph

                        I am excited to see this issue come up for someone else too.
                        I have a 2005 F150 4x4 with 28,000. My transmission bucks on CNG also. At first I thought it was a problem with the CNG kit. I removed my brand new exisiting multiport fuel injection system and installed another brand system. This time I installed a premium Technocarb multiport fuel injection system. Guess what? After many thousands of dollars and alot of extra work I completed the new conversion kit. I still had the same problem. When I am adjusting the fuel trim map on the technocarb system I can see the injector pulses. When I begin to accelerate or deselerate the Ford computer cuts the power instantaneously to the fuel injectors. It is just for a split second but then the transmission bucks. Sometimes it will buck 3 or 4 times in a row. I can see what is causing it. No power to injectors but I do not know how to fix it. Anybody have any ideas? It is not the Throttle Position Sensor, I already replace that.

                        Comment


                        • #13
                          Re: F-150 Buck/Jerk at 50-60 mph

                          Are you certain that the transmission is bucking? I was under the impression that a lean condition was causing a misfire in my intake manifold. In my case, installing new coils, plugs, and seals made my engine more responsive but didn't fix the buck. Replacing my coalescent filter fixed the buck, or at least caused such a significant improvement that I felt the bucking had stopped. The plugged coalescent filter seemed to be a possible cause of a lean condition.

                          The fact that you are having the same problem with a Technocarb kit is very discouraging. I thought that dumping my compuvalve for a Technocarb kit would be my salvation. Please keep us posted on any information you are able to come up with.
                          2001 F-150 5.4L Bi-fuel
                          7700 Extended Cab

                          Comment


                          • #14
                            Re: F-150 Buck/Jerk at 50-60 mph

                            So I finished and fixed my buck/jerk.

                            First replaced coil packs & plugs (no fix) nightmare
                            Second power flush the CNG system & replaced filter (no fix)
                            Third replaced all the o-rings on the CNG fuel injector sleeve (BAM FIXED)

                            My sleeves were so full of dirt and a few of the o-rings broke while I was taking them off the sleeves. On one of my injector sleeves the nipple was broken off inside of the CNG fuel rail. $230 for a new sleeve, however no one had them so I used epoxy and glued the nipple back on. BAM problem solved.

                            My suggestions to anyone venturing in to the coil pack/injector/o-ring realm do the driver side first on one Saturday then do the Passenger side on the next Saturday. The passenger side will require removal of the compuvalve. (Note: disconnect the red CNG connector before removing the compuvalve.)

                            -Harp

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                            • #15
                              Re: F-150 Buck/Jerk at 50-60 mph

                              It sounds like you had a lean condition and misfires causing the bucking. Unfortunately the o-ring solution will not work on my 2005 F150. It is an after market kit. However, maybe it is a misfire that is causing the buckaroo syndrome. I swapped a Throttle Position Sensor off of another gasoline powered F150 that had no bucking problem in hopes that it would fix my bucking problem. Guess what, the gasoline engine that ran good before I swapped it's TPS began to buck after I put the TPS from my bucking truck in it. The original bucking truck continued to buck even with the new TPS. Now I have 2 buckaroos.

                              This is the only vehicle that we have ever converted that had a problem after the conversion. Fortunately it was my own truck. I believe that the problem stems from the TPS and the ECU. The ECU is shutting down the injectors for a split second upon acceleration and deceleration. When the injectors turn off for that split second the transmission bucks. I am going to swap a Ford ECU from another truck with this truck to see if it solves the problem.

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