back pressure??

I recently installed a dual outlet header on my '87 4.0 and haven't hooked the exhaust to it yet, meaning the exhaust is coming just out of the header. My question is that I tried to drive it out of the driveway and it just puts. Would not enough back pressure have this effect or should I be looking at something else?

It's something else.

that's what i thought. I think that my fuel pump is on it's last leg and that was my first thought about this but wanted to check the back pressue issue. any other ideas. When I put the pedal to the floor it just puts along. Thanks for the repsonse.

Definitely something else.

I've beaten backpressure pretty well to death - backpressure is bad to begin with, which is why all-out performance engines run on open headers (you need some tube to help prevent valve warp - but that's about it. Running on open heads would make an engine last about two minutes from the overhaul...)

If you do some searching, you'll find out what I've got to say about it. I'd key on <backpressure> for posts with my username...

5-90

finding the threads, good info thanks.

Hum, not that I ever doubt 5-90... but...

Open header on a 22RE Toyota....wouldn't run at all. Connected exhaust....ran again like normal.

And recently, someone here on the board (or was it JeepForum?) posted that their 4.0L with open header would barely run. Reconnected exhaust...ran again like normal.

I would recommend reconnecting the exhaust and seeing if she runs before you start looking elseware.

No O2 sensor.

Prepmech said:

No O2 sensor.

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Bingo.....give that guy a quipe doll.

RickyN29 said:

Hum, not that I ever doubt 5-90... but...

Open header on a 22RE Toyota....wouldn't run at all. Connected exhaust....ran again like normal.

And recently, someone here on the board (or was it JeepForum?) posted that their 4.0L with open header would barely run. Reconnected exhaust...ran again like normal.

I would recommend reconnecting the exhaust and seeing if she runs before you start looking elseware.

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1987 XJ 4.0L/AW4 - open downpipe, ran like a BEAST for a week. Too bad I had to put the exhaust back on before the local constabulary took exception to my driving about...

The inlet for the muffler on my 88 has broken loose - while it's a touch noisier than it was, it also runs better - which is why I haven't been highly inclined to fix it... I'll probably put a cut-out in when I re-do the full exhaust next time...

It's possible that some production engines depend on backpressure - not for performance, but for emissions control - to cause exhaust port reversion. This has the effect of "tuning" the fuel/air mix - this has a lot to do, in fact, with the reason ChryCo could get away with deleting the EGR valve (not that the damn thing is necessary on RENIX - I've got emissions reports around here, somewhere, that show the engine runs cleaner without the EGR valve than with!)

I consider exhaust gas recirculation or "planned reversion" to be of quite dubious utility, but CalEPA and the EPA have both been sold on the idea (frankly, we'd be better off if we just got rid of all the bolt-ons and tuned the engine properly, but I don't see that happening... There's too much money to be made with emissions devices...) However, if an engine is designed for a certain amount of reversion at the exhaust port, it may run poorly (or not at all!) without it. This doesn't have anything to do with pure operation of the Otto cycle heat engine - just all the emissions crap we've been sold on (and don't need - just tune the engine properly and clean up the fuel so it's uncontaminated. Leave gasoline as just the paraffinoids that make it up, and quit adding crap that doesn't burn! If you add something to any fuel that doesn't burn, you've decresed the energy content - and the combustion efficiency - of the fuel...)

5-90

5-90 said:

"Always Available, Never Free."
- Bonus points to whomever can properly identify the source for that...

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Buck Godot... (Phil Foglio)