Engine Buck/misfire at speed?

Northwest_stang · Jul 6, 2019

So it’s a 2000 has 108k. I just ran some seafoam and then changed all the plugs. Apparently while I was screwing around with it a coil went bad In cylinder 3 but all of the boots are starting to crack so I’ll have to buy rest of the boots soon. Now the current problem is there is a very slight buck/misfire at idle but when at speed (50+) it is pretty damn noticeable. They are no codes and I’ve checked for the correct gap on every plug???? Any ideas what to look into next???

Fuel filter is about 6 months old as well

OneSick99GT · Jul 6, 2019

No codes. Hmmm. Bucking or surging can be numerous things. If I were you do a good tune up. Replace the plugs. Replace the ignition coils and see if the bucking surging goes away. If anything it will run a lot better. Ignition coils get weak and need replaced. They wont always throw a code when one starts failing. And when one starts to go the rest follow. I would start there. Have the injectors been cleaned or replaced. If they haven't I would replace those as well. Preventative maintenance is a must for any car over 100 k miles. Things wear out and need replaced. If I bought any car with 100k miles or more I would replace the plugs, coils, and fuel injectors right off the start so I know the engine is performing as it should. Then pull any codes, troubleshoot, repair and fix any remaining issues.

wmburns · Jul 6, 2019

One possible cause of bucking is timing related. One possible cause of unstable timing is cam (CKP) sensor. What's one possible cause of an unstable cam sensor? How about excessive AC ripple. What's one possible cause for excessive AC ripple? How about a bad alternator diode!

My recommendation. Do yourself a big favor and perform a through review of the battery and charging system.

Howto perform charging system voltage drop test

Howto perform charging system voltage drop test

To anyone else reading any of my posts I usually include the line: Today's cars simply will not run right without a strong battery and charging system! Cut corners here at your own risk I'm a big believer in starting with the basics. As such I...

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If a fuel injector problem is suspected I have had great luck with an injector cleaning and flow test service such as InjectorRX.com. Once cleaned and tested they are as good as new but cheaper.

Note, if the COP boots are visibly cracked then it's certain that some spark has been leaking out before jumping the gap. If allowed to continue long enough this will cause carbon tracking inside the COP coil. So be prepared that you could still have COP issues even after replacing the boot insulators. Note, I recommend always to replace the boots first before replacing the whole COP.

It would help to know which cylinders are misfiring. One of the easier ways to find this out is by looking at the ODB2 mode 6 data. Do you have an ODB2 scanner? if not, here's some information on an affordable Windows based unit.

ForScan ODB2 scanner w ELM327 USB

ForScan ODB2 scanner w ELM327 USB

While working on your car have you ever wanted: to find an ODB2 operational PID value (say fuel pressure or MAF)? How about graph a PID value over time? Or compare multiple PID's over time? Access a bi-directional PCM control such as test a...

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The "book" says to chase any misfire related issues first before moving onto other problems.

What have you done to rule out excessive EGR flow?

Northwest_stang · Jul 6, 2019

I’ll have to do a battery system test at the start of next week... my next days off lol

I plan on replacing all the boots in the next week or so. I had a misfire in cylinder 3 originally ended up being a bad coil so that was replaced. The egr valve is newish it’s also about 6 months old because the old one was old and sticking. A friend had mentioned that it’s possible a bad engine temp sensor can cause excessive egr flow but I know the thermostat is functioning correctly as I just did a coolant flush and thermostat tested. I might have s bad radiator ground that I haven’t been able to confirm. I have a low coolant light but it’s full and the recovery tank is a reman

OneSick99GT · Jul 6, 2019

Replace all the ignition coils. They can misfire and not throw codes. You will notice a big difference when you replace them all at the same time. The car will run like new with new coils, plugs and injectors. Timing can definitely be an issue but rare in most circumstances. Did you use a spark plug chart to see if the ones you had were good? I've attached one below for reference. Hopefully you did this. If you plan on taking the plugs out again take a picture of each one and label which cylinder it came out of. A lot of times you can diagnose whats going on by looking at a spark plug.

Northwest_stang · Jul 7, 2019

Yea I pay close attention to the things I touch because I’ve had the car about 7 months now and even though it’s low on miles maintenance was definitely neglected on it so I’m just working my way through systems but it’s like Pandora’s box. Fix one thing for preventative maintenance and it takes out a related system that was just barely hanging on..... I just have to remind myself that I love this car lol

But the plugs were definitely about 20% overdue based on run time. With cylinder 3 being the worst culprit. So I’ll have to keep an eye on things moving forward

Northwest_stang · Jul 9, 2019

*update*

Still have not had time to replace boots and I only have a cheap volt meter so I’ll just drop by the parts store and have them check it, there’s also an interstate battery on my way home. I was able to check connections on the O2 sensors and they are seem ok but definitely showing their age, probably oem. For some strange reason I found 3 lug nuts backed off to hand tight on driver front tire. I re-torqued them to 105 and will monitor. I also may have a bearing/hub problem on same wheel. When you spin it by hand you can hear and feel a tick as it passes a certain point in rotation and it is more noticeable going forward than backwards

OneSick99GT · Jul 9, 2019

Make sure to check the voltage system by following what burns said. Post the results here after you do it.

Northwest_stang · Jul 15, 2019

so finally had a day off and got the electrical tested. alt, dioed, everything on that side passed but came back with a bad battery and a failed starter. im hoping that its just the bad battery thats causing the starter to fail the test. I have never had a single starting issue. turns out right before i bought the car they bought and threw in one of those super cheap reman batteries from interstate.

so next step is to buy new battery and the coil boots

OneSick99GT · Jul 17, 2019

Sounds like you found your fix!

Northwest_stang · Jul 17, 2019

Has to wait one more week so I can buy a decent battery and not a Walmart pos lol but soon we’ll see

OneSick99GT · Jul 18, 2019

Don't go cheap on a battery. I've known too many people going cheap on batteries and you get what you pay for.

Northwest_stang · Jul 18, 2019

yea ill grab an interstate maybe an optima but well see

OneSick99GT · Jul 22, 2019

Update on this? @Northwest_stang

Northwest_stang · Jul 23, 2019

Had my cousins wedding this weekend so no time to work on it lol. I’ll be doing it this weekend and will post the update then

Northwest_stang · Jul 30, 2019

So new battery, coils and even had all the wheels rebalanced. So one problem down 2 more to go lol

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