Hello, I'm new to the forum. I have a question that perhaps someone here might be able to assist me with. - I have a 2001 Ford F150 "Step-side" truck with a 4.2L - V6 engine (with 202K miles) and an automatic transmission. - I stupidly used starting fluid to get the engine stared and the engine backfired (massively). I later learned that my problem was a bad fuel pump (for the second time), so I replaced it (again) and got the truck started. However, now I gave knocking noise coming from the engine and a persistent P0171 engine code (not to mention a rough idle), which may either be a stuck lifter, a bent pushrod, or possibly worse.

So, my question is this...if I find that the problem is NOT a bent pushrod or a sticky lifter (which are easy fixes), and I decide to swap out the engine, what are my options? Do I have to stick to the 4.2L - V6? Or, can I install a V8? Or at least a 4.6L - V6? I can certainly rebuild the old 4.2L, but is that engine worth rebuilding?

I turn to the those here, who have more insight than I for help....

Thank you,
Calixto

 

Your best bet would either rebuild the v6 or go with the 4.6l v8.

The cheapest would be to just rebuild the v6.

 

P0171 engine code is a lean code that makes me think the backfire blew off a vacuum line somewhere. If you could post a video of the knock, it might help us identify the cause.

 

A 4.6 swap is a lot more involved than you may think. Your transmission, PCM, and wiring harness all have to be changed.

 

Thank you all for the comments. - Regarding Roadie's comment about the vacuum hose...I wish!!! I've looked high and low for the vacuum leak, but have had no luck. I've been looking for a vacuum hose diagram for the 2001 F150 4.2L V6, but have not found one, so I have to search around blindly. Thus far I know the PVC value has vacuum, and all the hoses on top of the engine look OK, but like I said, I don't know where all the vacuum hoses are located, so its hunt and peck. I'll try to post a video of the knocking that depicts the sound as best as possible.

Thank you all and I'll follow up.
Calixto

 

You mentioned you had a massive backfire, did it go through the exhaust or intake?

If the backfire wen't through the intake, it could blow the intake gasket or crack the intake manifold.

A long time ago I had a massive nitrous (wet shot) backfire in my Camaro, it blew the intake gaskets and broke a valve spring.

 

Erik, to the best of my recollection, the engine shook quite violently and a bit of back-blow came up the throttle body.

Thanks,
Calixto

 

Hi Roadie, attached is the video you suggested I upload regarding the knock noise. I'm hoping its not a bearing or a piston rod knock and that its just a push rod or a lifter. (...but one can only hope).

Thanks for reviewing this ....

Best Regards,
Calixto

 

Sounds like a valve train noise to me.

 

Either valve train or you have a leak in your exhaust manifold.

 

Hello Gentlemen, thank you all for the input. I too think its a valve train issue. I suspect either a bent pushrod, a collapsed lifter or a broken valve spring. Although it does sound like an exhaust leak, I don't know if an exhaust leak would throw a P0171 (I may be wrong)...I've watched the O2 sensors on bank 1 and 2 and I can see Sensor 2 bank 1 go negative as the RPMs decrease, so the sensor is definitely picking up oxygen at low RPM. I would think that an exhaust leak would draw in more air at higher RPM rather than at lower RPM.

So, how does one test for an exhaust leak other than just feel around for it?

Thanks,
Calixto

 

You use an exhaust pressure gauge set. Threads into Oxygen Sensor Port.

Something like this: https://www.toolsource.com/back-pres...RoCGqoQAvD_BwE

 

Hi ManualF150...WOW. I had never seen one of those. Very cool...!!! Thank you!

 

Yup... I got this one from my local HF:

https://www.harborfreight.com/engine...kit-62621.html

Comes with even more fittings AND a case. I got it using a super coupon one day. I think I walked out of HF only paying ~$15 for it. Only used it a couple times, but man, it's nice to have the right tools for the job.

 

...oh man...., see what you went and did... I now have something new to buy at HF. (LOL)... Well, now all I need is one of those 25% off coupons and I'm golden.

Thank you!!!.

BTW, I found a couple of videos on YouTube that shows how to find exhaust leaks with a shop vac. - Interesting to watch.


Its worth a try...