I've noticed that my car makes the most power at 1/3 throttle. Any farther and it just bogs and makes even less power. Anyone know what that's all about? What's going on?!

Overly rich, under-volt, dirty rotor, mis-gapped, shifted points...

What car?


M

At what rpm? Carbs or FI? Did this just happen?

Something is big time wrong if that's the case. It should make the most power at full throttle. An engine is a pump nothing more, more air in more power.
Geoff

It's been running like this since I got it running. It's a 1.7 with stock D-Jet. I have a rebuilt distributor on order, so I'll see if that helps. It's got a Pertronix which I won't be switching into the new distributor right away. I'm going to hold back on that and run points for awhile just to make sure the Pertronix isn't a problem. It's got a new rebuilt alternator in it. I've suspected the car was running rich for awhile, but I don't really have the tools or the knowledge to know for sure. If I press the throttle to the "sweet spot" it pulls nice and hard (as hard as a 1.7 pulls) all the way to redline. Cap, rotor, wires and spark plugs are new. Plugs are gapped at 0.035 since the Pertronix puts out more power. It runs smooth when it's at the "sweet spot" so I don't think the gap is a problem. I bought the rebuilt distributor because there is a slight bucking while accelerating and I'm pretty sure it's related to the vacuum advance. So maybe there's some dynamic timing issues. Any more ideas? It'd be great to be able to drive my car out of town. Thanks!

Pressure sensor.


B

The TPS provides additional enrichment as the throttle plate is opening, until it stops moving. Does the car accelerate better while you are depressing the pedal, as opposed to constant position? If so then the problem is a lean condition, not rich.
I too lean toward the MAP sensor being the culprit, but I've never had that symptom with the D-Jet.

I'd suspect a fuel supply problem, maybe a clogged fuel filter, or maybe an intake screen clogged with rust.

seems like a leaky mps would be be in full rich position and run better as the throttle went down. and the TPS is for "accelerator pump" type enrichment, and would still work if the throttle were held in constant position.

but that's just my sense of it. i've been wrong plenty.

Maybe its that Napa Valley wine in the gas tank? LOL
Seriously, Brad is probably right. Check fuel pressure and pull a vacuum on the mps. I just repalced one this week, and man, what a difference.

I think that its both electrical and MPS. I think the dizzy's advance is not working rightand the MPS is having problems. A bad MPS goes rich but a car in good tune will still drive ok not the greatest but ok. Plugs will be black too.
Put a vacuum testor on the MPS to see if it holds 15hg for 5 minutes. If it doesn't hold a vacuum its toast.
Install the dizzy when you get it and see the results.

Geoff

Show us the vaccuum gauge you use Geoff.


B

I don't have the camera with me but I'll post a little tech article on "How to test one"

Geoff

I dont think you are supposed to re-gap the plugs if you use a Pertronix. They stay the same

Got my rebuilt distributor today, looks very nice. I didn't expect it to come with trigger points! Of course they're not brand new -- they've been bead blasted. I haven't installed it yet, but DAMN the shaft is tight in there. Now I know what a distributor is supposed to feel like! I'll get it installed tomorrow of Sunday and see how things are.

Mark..

can you stop by this weekend ?? I'll be around all day Sunday and Monday.


B

Forgot the image...