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| Runs well, but no throttle response https://www.slantsix.org/forum/viewtopic.php?t=25636 |
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| Author: | slantophile [ Fri Nov 02, 2007 7:52 am ] |
| Post subject: | Runs well, but no throttle response |
I have a dead stock 85 D100, 225 with a 4 speed OD. Anyway, the truck gets around well enough with light throttle application. I find it strange, however, that it seems to have less power when applying more throttle. Timing is right, engine seems tight. Any comments or ideas? Is it that under carburetated? |
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| Author: | slantvaliant [ Fri Nov 02, 2007 8:36 am ] |
| Post subject: | Re: Runs well, but no throttle response |
Quote: I find it strange, however, that it seems to have less power when applying more throttle. ... Is it that under carburetated?
Undercarburetion would show up at the higher RPM ranges, not as much in normal acceleration. Can you give us more information? Does it bog, then slowly pick up? Does it require feathering the throttle just to build speed? Lots of possiblities: Bad accelerator pump, fuel restriction, bad timing advance, etc. |
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| Author: | SlantSixDan [ Fri Nov 02, 2007 8:58 am ] |
| Post subject: | |
...exhaust restriction (quite likely on an '85), screwed-up lean burn, dead or dying oxygen sensor and/or other feedback fuel management components if so equipped... |
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| Author: | slantophile [ Fri Nov 02, 2007 9:32 am ] |
| Post subject: | |
The truck doesn't bog like an accelerator pump issue, and basically needs to be feathered all the time. I have not power with additional throttle, and instead run the engine to a higher rpm range under light throttle to accelerate more quickly. Basically, there is no perceivable power difference between having the throttle barely cracked open to wide open. The static timing is set to stock specs. It does not have lean burn. Interestingly, it has a fairly noisty exhaust leak under the hood when cold, but after about a half mile, the engine has much more power, runs smoother, and doesn't make the exhaust leak sound anymore. I haven't had time to look into the exhaust leak in detail, but it seems to be around the cat. |
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| Author: | Doc [ Fri Nov 02, 2007 9:36 am ] |
| Post subject: | |
Does the engine get any spark advance as the RPMs increase? Static timing is only the first piece of the timing advance curve, there needs to be some centrifical advance and vacuum advance to get the engine to develop power at higher RPMs. It is time to "plot" your advance curve using a timing light. DD |
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| Author: | SlantSixDan [ Fri Nov 02, 2007 10:10 am ] |
| Post subject: | |
The exhaust you hear leaking under the hood is getting sucked into the air cleaner via the thermostatic air cleaner. That'll put a hurt on performance, for sure. You'll definitely want to check the exhaust system for leaks and clogs. Doug's suggestion to plot the timing advance (or at least watch the timing mark with a timing light as you rev the engine) is a good one. Does your distributor have a vacuum advance pod on the side? |
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