Hesitation under idle & load AND mystery purpl/white wire?

[barneyhyphen]

1999 2 wheel drive 4.0 SOHC EB. 237,000 miles

Just replaced Plugs, wires, Intake manifold Upper & Lower gaskets, changed oil & filter and replaced fuel filter (old one said 09/01 on itso has likely got 200k on it!).

Also cleaned throttle body, MAF and IAC.

Car is much peppier BUT has very rough idle and stumbles under load (up hill). At steady 50 MPH not too much problem but you can still definitely feel a "miss". No codes after 50-60 mile of driving.

I'm real meticulous when doing these jobs and have also gone back to check my work. Everything "appears" to be good but the problem was not there before I did all above and it had two old plugs which I think may have been original to the car! Both center electrodes burned away with a 90 + thou gap but apparently still firing.

The ONLY "problem" is that during the work, a small wire has come detached and I can not find where it belongs. It's PURPLE/WHITE, comes in to the engine bay, through a hole in the firewall, just below the throttle cable and is about 24" long. Will reach about as far as the steering resevoir. It comes through the firewall in a black wire protection casing with a second wire. The second wire detours about a foot out from the firewall, over towards the driver's side fender then heads to a plunger switch in the front driver's side corner of the engine bay, which is actuated when the hood is opened. I'm assuming the plunger switch is part of the alarm system (VIPER).

Because the mystery PURPLE/WHITE wire comes through the firewall together with this second "plunger" wire, I HAD assumed the P/W wire was also part of the alarm system? Perhaps correct, perhaps not?

The end of the P/W wire is clean and appears to have been soldered.

Any input/advice on either/both the hesitation &/or the purple/white wire would be very much appreciated. Thanks.

 

[audiomax]

Some viper alarm systems use a purple/white wire for the tach input wire, not knowing the exact model of the alarm really cant say for sure, but sounds like that may be what it is for.

 

[Midwest Dually]

I am not sure about the P/W wire, however for the stumble and miss under load and throttle I think the next step it to check injectors.

I recently discovered that even with a 6-cylinder, that one injector can fail and it will still run, even smooth until a load is put on it. Of course checking the harness is important (using a test light or noid light at each connector to make sure current is going through the harness).

A simple test I use is to unplug each injector, ONE AT A TIME, and run the engine up through the RPMs with a good amount of throttle. If the engine does not change in performance on one of the injectors, then its dead and time to replace.

I had lots of suggestions that it was my coil pack, but I have never seen nor heard of a coil pack failing like this, and there should be a code thrown if it does.

I had this issue for some time and never got a single code, even under live data stream tests. It wasn't until I put enough miles on mine and wear that the injector started getting worse, and a misfire code came up on one of the cylinders, that I started looking into the injection system. And even at 60,000 miles, the injectors can still fail!

Give it a test and share the results!

 

[barneyhyphen]

Thank you for all the input, very much appreciated.

Did I originally say I was METICULOUS? Well...last night I decided to remove the PCV I cleaned and replaced. Rattling very freely so assumed ok. Gave it a simple blow/suck test, only to find it was NOT closing, so replaced with a new one immediately. Problem solve, yes? NO.

I have, for two days, on two separate occasions, got a misfire on cyl 3 code P0303? No other cyl's, just on 3. So, this morning, decided to remove new lead and test continuity (good) and also test the new plus for resistance and make sure it wasn't shorting. ALL tested out very well.

However, when attempting to replace the boot on the plug, I felt it seated much firmer than before!

Yes, problem solved, runs like a top.

Lessons learned... Double check everything you do. keep the problem solving simple (start with the most obvious, even when you think you did it properly).

Thanks again.

BH

 

[barneyhyphen]

So, if we were to assume the Purple/white wire IS associated top the VIPER and IS the "tach input wire".....where in the engine bay and to what might it attach?

Thanks.

BH

 

[audiomax]

It would connect to the Tan/Yellow wire on the coil pak,

 

[barneyhyphen]

Thank you very much for this info. I'll get it all hooked up tonight.