1993 runs rough

A

AnotherMotorist

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engine runs but it's choppy. It has good vacuum but with all the vacuum and intake on it seems to stutter and lag at low rpm. I can rev it up high and it runs pretty good.
A few weird things:

I have a vacuum port open and if i plug it while it's idling it slows way down and almost dies. Is it not getting enough air? Is it a sensor? Map sensor reads good voltage. Same with tps.

Fuel pump doesnt work with key on but with engine running it has 30 psi at idle and increases to 40 when i rev it.

Exhaust pops and sputters at idle. Is the timing off?

I'm wondering if all this might be some sensor. Brand new intake manifold and air filter, throttle body is clean.
 
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need to know more, 4 or 6 cyl, stick or auto ? where is vac line that you plugged located? with new intake, it might not be tight? gasket not seated? what is you timing reading right now?
 
It's a 4.0 6 cyl with an ax15 manual.

Right now i have the vacuums all connected, but i don't know if they must go in exact ports or if they're all equivalent. Fuel pressure regulator is on top forwardmost, map sensor goes to the side, brake booster is going to the top rear one( that's the one i had open).

I have not checked the timing and i suspect that could be a problem.

It idles ok but it'll slow down after 10 seconds or so, then speed up again, and it might die altogether. When i rev it up it's uneven like it's missing a cylinder. It also stutters to catch up when i give it throttle, like not enough air somehow.

Took off the idle air control valve and it was all gunked up. Whole intake manifold is new and clean inside though.
 
The timing is essentially controlled by the ecm. Unless you installed the dist a tooth off trying to time it will be futile. Id dig around for a vac line schematic just to be sure everything is plugged in correctly. Not saying your ecm is bad but they do go bad sometimes. Might give www.wranglerfix.com a call if you suspect it might be after other tests dont correct the issues.
 
I had a slightly rough idle in my 2.4L so I tries a few tanks with the Lucas fuel additive which is not really a cleaner but more of a lubricant. It helped but still not 100%

Last month I installed rebuilt injectors from K Suspension and that solved all my problems. Also the MPG's went from 14 to 15.8 after 1/2 tank test.
 
Interesting point about the ecm. That reminds me of another thing.
The fuel pump doesnt run with the key on.
If I hook the wires straight to the battery, works great.
Plug it in at the connector where it belongs and turn the key, it'll run for half a second and quit.
But the engine will start just takes a second or two.

Voltage reads 8 at fuel pump connector with key on, drops to 7.5 when you crank the engine.

Could this all be the computer?
 
AnotherMotorist said:
Interesting point about the ecm. That reminds me of another thing.
The fuel pump doesnt run with the key on.
If I hook the wires straight to the battery, works great.
Plug it in at the connector where it belongs and turn the key, it'll run for half a second and quit.
But the engine will start just takes a second or two.

Voltage reads 8 at fuel pump connector with key on, drops to 7.5 when you crank the engine.

Could this all be the computer?
Click to expand...

Yes it's the computer but that's how the system works. If the engine is not running, the pump may run for a few seconds to prime the injectors. If primed, the pump won't run until the engine starts or maybe if the key is turned to the start position.
It's a safety feature which cuts off the pump in an accident type situation where you don't want to keep pumping gas after a crash. Most all cars have this.
 
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I know this is minor, what plugs are you running, wranglers work there best on champion 412{RC12LYC}, when was your last tune-up?
 
93 wrangler 4.0 engine

I bought this as a project, guy before had redone everything from the frame up. Ford axle swap, spring over lift, upgraded steering, etc. The sensors and most electrical was all plugged in, but there are about 7 connectors near the driver side firewall that arent plugeged in. Guess i forgot to mention that! I just don't know very much about wiring an engine. I have tested the map voltage, bought a new one anyway, waiting for new iac sensor.

It seems to be an air problem, when i unplug the brake booster vacuum it instantly runs better. But even then it stumbles, and sort of jumps/skips/ misfires, not sure which. I just know it's not smooth. Maybe fuel/air mixture? Sensor not reading right? Computer or ground somewhere? Seems like it could be one million things.

Theres no vacuum on the distributor as i understand, gila guy said the computer controls the timing. The distributor was installed before i got it and it seems to have good spark on every wire
 
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