Bucking / Surging Issue

rondon281 · Aug 6, 2019

Before I get into my problem, let me tell you about my 1995 Mustang Cobra. 73K original miles. Motor internally is stock. LT headers, OR H pipe, flowmaster 40's, CAI, 75MM MAF, 70MM TB, MSD distributor, coil & wires, new autolite plugs gapped .054, new TPS. IACV about a year old. New adj. FPR with pressure set at 40 and new fuel filter. Ran a car of Seafoam through the tank about 3 months ago. Car has been tuned. The problem is intermittent. Bucking / surging while accelerating or in 5th gear cruising at 70mph. Car will surge and lose power for a couple of seconds and then accelerate. Does not do this at idle, only under load. I replaced the TPS and the problem went away, for a while. Now it's back. Any thoughts to the problem?

jozsefsz · Aug 6, 2019

Usually this indicates you're not getting enough fuel - fuel pump pushing inadequate volume or tune's accelerator-pump settings not 100%. I'd also suspect the MSD ignition components - very poor quality in my opinion, still riding on the tails of their old reputation. Those 'blaster' TFI coils are prone to very early failures and leaking, and their wires are prone to arcing at the distributor. I chased a spark blow-out on my turbo 5.0 (similar symptoms - stomp gas and go completely flat) for a few days until I replaced the coil with an Accel.

rondon281 · Aug 7, 2019

jozsefsz said:
Usually this indicates you're not getting enough fuel - fuel pump pushing inadequate volume or tune's accelerator-pump settings not 100%. I'd also suspect the MSD ignition components - very poor quality in my opinion, still riding on the tails of their old reputation. Those 'blaster' TFI coils are prone to very early failures and leaking, and their wires are prone to arcing at the distributor. I chased a spark blow-out on my turbo 5.0 (similar symptoms - stomp gas and go completely flat) for a few days until I replaced the coil with an Accel.

Thank you for the info. I've wondered about the fuel pump, as it may be original. Would you suggest replacing with OEM or afternarket? I'll also talk to the speed shop that did the tune.

jozsefsz · Aug 8, 2019

I've been happy with my little Walbro 255lph pump for a number of years, very solid units if a little noisy. OEM's lasted for 25 years so if you don't have more extreme build goals I think it's aok too. If you are running an MSD coil, do at least try and swap that out with the stock one if you have it to see if your situation improves before dropping the tank, though there's nothing wrong with preventatively changing the fuel pump after a lot of years anyways.

rondon281 · Aug 8, 2019

jozsefsz said:
I've been happy with my little Walbro 255lph pump for a number of years, very solid units if a little noisy. OEM's lasted for 25 years so if you don't have more extreme build goals I think it's aok too. If you are running an MSD coil, do at least try and swap that out with the stock one if you have it to see if your situation improves before dropping the tank, though there's nothing wrong with preventatively changing the fuel pump after a lot of years anyways.

I do plan to rebuild the motor at some point, but I will probably stay NA. The 255lph seems a little much, if you don't have a power adder. The stock pump is rated at 95lph, so I was considering 155lph? I'll have to get my hands on a stock coil, as I threw the old one away. The pump on my '98 cobra just quit one day, while I was on the road. Obviously had to have it towed. I think I'll replace the pump, so I don' have that problem. Thanks again for your input. Definitely helps.

Noobz347 · Aug 8, 2019

...and a set of non-FMS plug wires. Taylor or OEM would do.

rondon281 · Aug 9, 2019

Noobz347 said:
...and a set of non-FMS plug wires. Taylor or OEM would do.

I know I'm going to sound like a moron, but please explain non-FMS plug wires?

Noobz347 · Aug 9, 2019

rondon281 said:
I know I'm going to sound like a moron, but please explain non-FMS plug wires?

Sorry... Plug Wires made by Ford Motor Sport. I could see arching in the engine bay with every set I've owned.

Some folks on this very forum swear by them. Not I

If I were given a set, I'd drop em in a trash can.

rondon281 · Aug 9, 2019

Thanks

Bucking / Surging Issue

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