1999 EX lacks power/acceleration

skrieck · 10-10-2009

Recently acquired 1999 EX. w/90k miles. Seems pretty underpowered. Performed tune-up (definitely needed plugs and timing adjustment, repl. distr. cap, rotor, & fuel filter, air filter clean) with surprisingly little effect. Compression check: 190, 191, 197, 201; ran a tank of fuel with system/injector cleaner, and a couple of tanks of premium - no effect; ran a couple of doses of sea-foam through vacuum port into combustion chamber, with very slight improvement in performance. Post-sea-foam compression check 200, 201, 200, 205. Vacuum check was spot-on with factory specs.
Brought to dealer - they spent a day and couldn't find anything wrong; checked cam timing; checked for exhaust blockage found none; interestingly, they said the air intake set-up wasn't exactly right (the car had been in a fender bender and apparently resulted in part of the plastic intake duct being partly obstructed, which I hadn't noticed) which they rectified. They ended up saying they thought nothing was really wrong with the car (!!??) When I got the car back from them, it did have a bit more power, small amount but noticeable going up hills (air-intake result?). Still, when I press accelerator gradually there is very little response and I just keep pressing and pressing until finally the trans downshifts and I'm revving 4000-5000 rpm and finally accelerating. My mother's 2000 LX w/50k more miles, and my sister's 1998 LX w/35k more miles have noticeably better acceleration in comparison.
Any ideas about what might be the issue here??

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gearbox · 10-10-2009

have you tried cleaning the intake system? throttle body, idle valves, etc. they tend to get gummed up with carbon. you sure the ignition timing is good? and be sure to use 87 octane for the most power. its also possible you have a clogged cat converter, not enough to cause problems yet, but blocking some airflow so the engine feels stuffed.

skrieck · 10-10-2009

Thanks for the notes.
The sea-foam through the vacuum port should have addressed any carbon in the combustion chamber, and it is fuel-injected. I did not perform the first sea-foam treatment, but the mechanic who did assured me that there was a decent amount of carbon cleaned out; I performed the 2nd treatment with almost no additional results, so I assume it is pretty clean in there. The mechanic at dealership assured me he checked for exhaust/cc blockage (probably blow-back test) and there was none. I set the timing to factory spec, and I'm assuming the dealer probably just double-checked it to be sure.
Thanks,
Skrieck

gearbox · 10-10-2009

did you get the engine valve lash adjusted? they may be too loose and that will cause power loss. usually every 100k they need adjusting but sometimes sooner depending on driving habits.

skrieck · 10-11-2009

I'm not hearing any valve tappet sounds, which I think would be quite audible if the adjustment were so loose as to actually cause power loss. I've never had an engine with an overhead cam though, so maybe valve sounds or lack thereof is different for this kind of setup - easy enough to check the lash though.
Thanks for the suggestion.
Oh, and it just occurred to me that if there were lash issues, then I probably wouldn't have gotten such good compression readings. The compression readings were quite good. (184 being "normal", mine are around 200)

gearbox · 10-11-2009

well if its that high, usually means there is carbon buildup on the pistons. which i guess is a good thing since it raises compression. not really sure what else you can check. just be sure all the parts you use are good quality like ngk plugs and wires not cheap generic stuff.