Hesitation when warm

[JooF]

Well, all is well after my VSS replacement... except I still have a fairly nasty bog in the gas pedal when the engine has warmed up. When I first start it, it feels eager to accelerate, absolutely no hesitation, but after it warms up, the first 1/4 inch of the pedal feels pretty dead kinda almost have to push past it to get the van to react. I am pulling no codes. What happens after warm up? There is definitely a difference in performance after warm up. The thing that throws me is that it almost seems like its not as bad some days... Gonna go poke around for a vacum leak, hopefully someone can shed some light in the meantime.

Any experiences welcome!

[JooF]

Sorry, neglected to mention it is an 87 with TBI.

[davesyo]

One thing that comes to mind is the throttle position sensor which can cause hesitation

[johnny-77]

Ive had identical problems when a O2 sensor was just starting to go bad it would work but not fast enough. The computer did not catch it, but watching a scan tool live data read out made it fairly apparent it was not changing values very fast when the pedal was pushed.
Hope this helps11 :2cents:

[Big_kid]

I had a similar problem in my 87 S10 (2.5Liter, TBI). I'd leave the house in the morning fine. I'd pull out of the neighborhood into traffic, and I had to floor it, it would take 3 or 4 seconds, then finally decide to give me all it had. I checked voltages, sensors, all kinds of stuff. I eventually checked the antifreeze, and it was low. Once I topped it off, it never happened again. The only thing I figured was the actual engine temp was different that what the water temp sensor was reporting, causing incorrect mixture/timing for actual operating temps. This would be overridden when I floored it for a few seconds, when the computer would go full advance & rich mixture for max power. I had done a tune up, cap, rotor, etc, it ran better when it ran but still had the hesitation. I replaced the O2 sensor, it gave 3 times the improvement the tuneup did, but it still hesitated. Topping off the antifreeze cured it for me.

Check your coolant, and make sure it is filled COMPLETELY. My buddy's 98 S10 would act the same way when it was less than a quart low.

Good luck, let us know what you find!

[JooF]

Thanks fellas, I installed a new O2 and am getting much better fuel milage. The coolant was full at the rad, but I did have to add a lil at the reservoir. Next time Im under the shroud I will look for vacuum leaks and replace the tps and plugs, leads, and rotor/cap. Is there a thread for any cold air intake ideas? Anyone ever try a throttle body spacer?

Met a guy the other day locally with a V8 Astro, we talked briefly about turbo charging. The van certainly could use some more ponies... now that Im not getting 8 mpg!

[johnny-77]

Ive installed them for other people. Some seem to help others do not work at all, but the ones that seamed to work were mostly composite not metal. The power gains were modest but detectable on a G meter. The thicker and longer thy were in most cases the better the gain. I can only assume it has more to do with intake temp as much as any thing .

[JooF]

Welp, on a hyway trip today it started a new trick! That lil bog at part throttle has now become what I like to call "megabog". Anything past 1/4 INCH of throttle slows me down, it made for a rather interesting trip to say the least. I was pretty low in the tank, not at empty, prolly a 1/4 tank on the gauge... tossed 20 bucks in about halfway through my trip, went up to half tank<seems like a small 1/4 tank if you ask me> and it seemed to clear up a bit after about 20 kilometers, but it is still very noticeable. The SES light came on a number of times, Im gonna run down and pull the codes...

On a happier note, my buddy gave me an intake manifold from a 350 truck. The body is still there with the TPS, but the injectors are gonzo. Are the throttle bodies a match? Im not sure what Ive read but I coulda sworn something was larger... injectors?

[JooF]

Ok then, code 44 - "oxygen sensor lean exhaust". Gonna go tear into it... suggestions welcome!

[JooF]

No fuel pump. Engine cover is off, gonna wait till I take care of the fuel pump before changing anything else. There is absolutley no "5 second hum" from the tank with key at run.

To be continued....

[specelec]

It kinda sounds like the problem that I had with a plugged CAT. It was like there was a point on the pedal that if I pushed it past that point it would bog down and I would slow down....NOT NICE when entering a freeway!

Hope this helps.

[JooF]

Just to wrap up this thread, I ended up replacing the pump, rebuilding the tbi and forgot about the fuel filter. It ran well but had no power after about an inch of pedal... fuel filter is installed now and the van runs fabulous!

Thanks to all for your comments, its nice to have a bunch of gear heads to talk with!