Contour Enthusiasts Group Archives Forums General Troubleshooting Slight hesitations under full throttle

Well, I've just recently started experiencing slight hesitations under full throttle above 4k rpms. It seems to start just after the secondaries open up. From searching it seems that this could be the fuel pump starting to go? However, I also have been throwing an intermittent CEL 420 for the past month or so. Could these somehow be related? Maybe new plugs are needed? It's a '99 SVT with 44k on it. I don't want to just start throwing parts at it so... any advice?

Thanks,
Jay

sounds more like a TPS (throttle position sensor) problem, especially if you're getting a CEL also.

I'm having the same problem, except mine only seems to manifest itself on the highway above 75mph. No one's been able to pinpoint the problem, but here are some possible diagnoses:

Improperly spaced plugs
Bad fuel pump
Overheating tranny
Vacuum leak
Secondaries/intake gunked up
Cats/Pre-cats plugged or bad

Do you get a sulfur smell at WOT? Someone mentioned to me that is an indication that raw fuel is making it to the cats, which may be caused from improperly spaced plugs.

For the fuel pump, people have mentioned that the problem gets worse/better depending on how full the tank is. You may want to pay attention to see if the hesitation fluctuates.

For the tranny, I checked the fluid, and it seemed a little funky. If yours smells burned, get it changed right away.

A vacuum leak is the hardest to diagnose/fix. My car whistles after running for 15 minutes or so. The mechanic at my local Ford dealer said he could completely disassemble the engine and rebuild it and still not find the leak. Best thing to do is check the intake and related hoses for dryness/cracking.

You mentioned that it seems to happen right after the secondaries open up. Could be that the secondaries need to be cleaned, or maybe the MAF. Many people have reported that a good cleaning of the intake can make a big difference in performance.

Lastly (finally!) you mention you get a 420 code. I did a quick search, and came up with "Bank one Catalyst below threshold" which means something may be wrong with your cats. You might want to read more here.

Hetfield--Awesome reply!! Since you took the time and energy to post such an educated and concise reply I'd like to take the time and energy to point it out and say thanks! I really enjoy reading posts like this. This is what the CEG is all about.

Hetfield,

Thanks for all the info.

No fulfer smell.

No change depending on fuel level or brand.

Not sure how the transmition fluid comes into play with this, but I think it's fine. The tranny was replace at about 22k by the dealer. So the fluid only has about 22k on it.

All hoses and such look fine and there aren't any audible leaks.

The intake and MAF could need cleaning. Is that difficult to do?

The CEL 420 may be just the O2 sensor or what's going on now, but if not then the cats should be covered.

Louisw,

Throttle position sensor? Hadn't heard that one before. Do you have anymore info on that and how it might be tied to the CEL?

Thanks,
Jay

Originally posted by SVT-N:

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Throttle position sensor? Hadn't heard that one before. Do you have anymore info on that and how it might be tied to the CEL?

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Nevermind. A flakey TPS sensor will also set off a CEL and I thought that might have been it.

I'll give one vote for aging spark plugs.

I'll second that vote, DemonSVT. I've been wanting to get some Bosch Platinum +4's for awhile now anyway.

Thanks,
Jay

Originally posted by SVT-N:

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I'll second that vote, DemonSVT. I've been wanting to get some Bosch Platinum +4's for awhile now anyway.

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I'd go with factory double plats. I've had Bosch +4s for ~25k and though I have had no problems so far, they seem to be wearing unevenly. The front bank is the one wearing fast, strangely enough. Go here for more info.

Originally posted by SVT-N:

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I'll second that vote, DemonSVT. I've been wanting to get some Bosch Platinum +4's for awhile now anyway.

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Most definitely stay far away from any POS Bosch plug!

Use either Motorcraft AWSF32PP or Autolite APP764 plugs.