I did a smoke test on friends newly acquired ranger. It was idling rough. After cleaning out the leaves and nuts in the air box it ran a bit better. Cleaned the maf, iac valve, new plugs, wires, one wire was broken inside at plug connection. New air filter. Still rough idle. Checked vacuum. Only has 12.5 to 13 at idle. Sprayed some carb cleaner around and found no change in idle speed. Smoke test yielded a questionable result. A small amount was coming out of the throttle body where the butterfly pivots. I was told that it's not an issue by another ranger friend. Is it true? See attached picture where it was seeping from.

Whisps of smoke in area of red circle
If this small whisp of smoke is ok, then vacuum leaks. I will pull the iac connection and see if idle goes to 500 or dies, this will also confirm no vacuum leak, right? Once i get his throttle body back on, that only had 3 bolts holding it on! one was missing. Gotta love used cars. Oh yeah also the egr was no good, would not get any vacuum, so i put one on from the u pull it yard, and it tested good. It also has and exhaust leak after the O2 on Bank 1 at end of fist cat. Small hole. Will that cause low vacuum? Passed injector leak test. I have run here, my main question was smoke at the butterfly?

 

Throttle plate rod air leak wouldn't cause an issue, you would get lean codes on both banks BEFORE there were any running issues

With Misfires you need to do compression test first
Gasoline engines burn exhaust valve, just the way it is, so best to take that off the table first

Run some injector cleaner in the gas tank, Seafoam or similar
Dirty injector tips can DRIP fuel at lower RPM vs higher, and air flow is slower so larger droplets of fuel doesn't mix as well and you get rough idles, misfires and partial misfires

Alternator has 2 bad fields if idle voltage at battery is 12.5v to 13v
Minimum alternator voltage at 700rpm should be 13.5v-13.8v and just after startup up to 14.8v

Alternators have 3 fields that generate voltage
1 field failing gets idle voltage just under 13.5v, and dimming head lights at idle
13v or lower means 2 fields are bad

 

Thanks Ron. Alternator voltage was 14.4 at start up. I'll check it again this weekend. Along with compression and fuel pressure. His truck has NO codes. At idle the fuel trims were a bit off in my opinion, but I'm just starting to learn them. Compared to my ranger they are a bit off at idle, and at 2000 rpm level out to about 5. At idle i got about....
STFT bank 1 (+4 to +7)
LTFT bank 1 (-10 to -7.8)
fuel trims should equal 0 as I understand it. If so, Bank one at idle looks like it's near new lol.
STFT bank2 (+2.3 to -.08)
LTFT bank 2 (+12.5 to +13)
I guess that's not too bad, close to 10 total.
O2 sensors are reading like they should, I know they are based on my 9-month ordeal with my Rangers computer and cats. lol.
Vacuum at idle is 12.5
Vacuum at 1000 rpm is 10
Vacuum at 2500 rpm is 15.
Not sure what to make of that. I have run on again, sorry.
I'll run some more diagnostics this weekend and ask for more help after that, I'm sure!

 

The way fuel trims work, is that STFT includes LTFT

LTFT is in memory, so engine can run OK when cold when O2 sensor can not function and give computer feedback

And its also used after warm up

Computer uses tables in memory to set air/fuel trims when engine is cold, and it ADDS LTFT to that table

After warm up computer calculates STFT on the fly, and LTFT is added to computer's STFT 0 to give the new STFT 0

So if LTFT is +10% the STFT 0 is actually +10%
So if STFT is +5% and LTFT is +10% then its really running at +15%

The reason for LTFT is so the engine system can age gracefully
There will be small air leaks, the MAF will get dirty, fuel pressure can drop a bit, injectors get dirty, and number of small things, engine still runs fine
LTFT is there so computer doesn't have to LEARN the aging engine system every time you start the engine

LTFT is self correcting
Say you had old O2s and changed them, old O2s show FALSE LEAN
So LTFT was probably high, say +15%
With the new O2s and after warm up, STFT would/should show -1% to -5% and the longer you drive that more LTFT will correct itself, goes down to +10% and +5% and STFT gets closer to 0

So anytime you do repairs, i.e. fix air leaks, clean MAF, use injector cleaner, new air cleaner, new fuel filter, ect.............
You need to drive for a few days to see if LTFT is self correcting

Most OBD2 readers can not Clear LTFT, some can, I know Ford shops can
The reason is described above, if a novice cleared LTFT then engine would run like crap on cold start if they hadn't fix the problem(s), lol


Your Vacuum is way too low, bad gauge most likely, I don't think it would cold start with vacuum under 13"

 

Compression test yielded results that were not favorable.
Bank 1
1-30
2-130
3-130
Bank 2
4-145
5-145
6-150
#1 wet compression was the same 30. Upper end, I guess. Probably the burned exhaust valve, maybe, But the 2 and 3 cylinders are a bit low also, compared to my Ranger.
On that note there were no codes, and no check engine light.

 

Bummer, but at least you know where to start

You can do just one head, but best to do both, flex fuel heads have different chamber shapes than gas only heads
But you CAN uses two gas only heads to replace the two flex fuel heads with no issues even running E-85, they are often cheaper and easier to find
But I wouldn't use one of each

If time is not an issue then have your head(s) rebuilt

 

Thaks for your wisdom again. Good news for me is this was not my truck lol. It was a friend that bought it. I guess the lesson here is that if I you look at a used vehicle with rough idle, bring a compression gauge!

 

Cylinder one-Never have I seen a valve that looks like this.

 

Yes, that is pretty nasty
Probably stopped rotating