Driveability Issues after 4.6 Install

Performance mods and Advanced Stroker discussion.
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JeepJerk
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Joined: June 27th, 2019, 7:52 am
Vehicle Year: 1998
Vehicle Make: Jeep
Vehicle Model: TJ

Driveability Issues after 4.6 Install

Post by JeepJerk »

So I finally got my stroker installed after an entire year fiddle-f**king around, got it running and having some stupid problems.

No codes being thrown at this time.

1. Starts up fine, when first driving after anywhere from 15 seconds to 1 minute it sputters and loses power. I have to pull off the road and let it idle for 15-30 seconds, seems to help if I rev it a bit during this exercise. Then it returns to 'normal' and doesn't do it again until it's shut off and restarted. Even if I shut it down for just 1-2 minutes it does the same thing again in the same time range, so I don't see how this could be anything other than a computer/sensor issue.

2. Randomly elevated idle- this happens about 2 out 3 times it's driven. It'll idle normally around 800rpm, then out of nowhere the idle will be at 1200, 1500 and as much as 2000rpm. This will happen after driving for a few minutes and will just keep happening....after sitting at idle it will drop back down to 800rpm (but not always). No vacuum leaks.

3. Seems to miss a little at idle. Could this just be the cam? All electrical components are new including the distributor.

4. Not very smooth through the RPM range- even when it's running normally it seems to take off well but gets a little sluggish and jerky between 2500 and 3000 rpm. This is slight but noticeable.

The build is .030 over pistons, 4.2 rods with a CompCams 252 cam. It ran normally before I broke a piston and pulled the engine last year.

I'm planning to upgrade the injectors and fuel pump, not sure what else I ought to do. Confusing since I'm not getting codes and this really seems like it must be related to the computer and/or possibly MAP, IAC or something of that ilk.
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Cheromaniac
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Joined: March 8th, 2008, 12:58 pm
Stroker Displacement: 4563cc
Vehicle Year: 1992
Vehicle Make: Jeep
Vehicle Model: Cherokee
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Re: Driveability Issues after 4.6 Install

Post by Cheromaniac »

You could try cleaning the inside of the TB and the IAC valve. This might just help the idle issue.
Test the TPS voltage by slowly opening the throttle blade with ignition on engine off. It should ramp up smoothly from ~0.7v to ~4.3v. If there are spikes or troughs, replace the TPS.
The MAP sensor rarely fails but you could have a cracked or broken vacuum pipe leading to the sensor and that can cause havoc.
1992 XJ 4.6 I6 - 5MT - Stroker build-up, Stroker "recipes" Sold
1995 Mustang GT - 4AT - Modded Sold
2006 Mustang GT - 5MT - Modded Midlife Crisis Car :mrgreen:
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