What other issues can mimic a vacuum leak?

Originally Posted by clinebarger
I would inject some propane into the brake booster hose while idling, The front O2 sensor voltage & Fuel Trims should respond immediately if a actual lean condition is present!

What is the O2 sensor doing.....If it's dropping to Zero Volts or close to it....That will cause the system to go Open Loop. This could be from a excessive lean condition OR a faulty Heating element in the O2 sensor.

The PCM does monitor the O2 Heater Low Control, But just checks for a 12volt return from the HO2S Heater Fuse IIRC. Not amp draw to indicate the heater is actually working.

Dont know if I agree with that logic.............. injecting anything into the booster line is bound to upset/change the O2 voltage anyway regardless of vacuum leak's presence.
 
It's more about checking the O2 sensor response. A faulty O2 heater can cause open loop operation at idle.

I still think it's a vacuum leak but I'm spoiled by a smoke machine & would have eliminated that possibility first.
 
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So... I'm starting to think that the old MAF is closer to reality than the new one is.

I needed a third car for today, so I decided to get the truck put back together and out of the garage. So first, I did a bit of tightening on the exhaust flange ahead of the O2 sensor. No change.

Then, I took off the upper intake manifold and replaced the intake side spark plugs (dual spark). Wow, they were worn! While I was there, I popped out the fuel injectors and took a peek at them and replaced the o-rings on them. Everything looked good on the injectors. Put it all back together with a new gasket. Cleaned the IACV while everything was off.

Then, I decided to replace the exhaust side plugs too, so I did that. They were just as bad. All Motorcraft, were they original at 265k miles? Who knows?

Put it all back together with the old MAF and when I started it up, I had +20 STFT and -20 LTFT and with time, they converged close to zero with STFT zigzagging back and forth. Looked pretty good to my inexperienced eye.

My old MAF shows about 3.2 g/sec at a 800 rpm idle. Not sure if that's high or what, but I took the truck to work (20+ miles) and it ran OK with no check engine lights. On the drive in, LTFT is running around -10. At idle, it tends to be closer to -5 and driving around, it's a bit up and down. Idle is OK initially at 1000 rpm, but after idling a couple of seconds, it settles down into the 750-800 range and you can feel quite a bit of vibration.

... so here's a little more back story...

I've had this thing about a year. The truck always had some vibrations at idle. A few months ago, the CEL came on with a P0172 (rich) code. I saw what I assumed were higher than correct air flow at idle and replaced the MAF at that time. The CEL went away for a while, then it started running rough and gave a P0303 (cylinder 3 misfire) code. I found that STFT was getting really high (+32) and causing the car to go into open loop, then in open loop it was misfiring. Revving the engine brought down the STFT and put it back into closed loop. I assumed the new MAF was the good one and started hunting for a vacuum leak...

With the new MAF, at idle, you can watch the O2 voltage and it just stays low (0.2V or whatever). It only spikes up if you give it gas.

With the old MAF, O2 voltage is swinging back and forth regularly. It takes about 3 seconds for a whole cycle. (seems slow to me)

I think I'm going to drive it as-is on the old MAF for a while and see if the P0172 pops up again...
 
One other weird thing is: with the old MAF, if you get it and turn the key all the way to start, it will initially begin to start, then it will start to stall (sometimes actually stalling), then revs will pick back up to normal.

With the new MAF, when you do that, instead of briefly starting to stall, the engine surges briefly, then revs drop back down.

If you key on for a couple of seconds before engaging the starter, it starts fine. Previous owner said it had a weak fuel pump, but I have replaced the pump and filter and it still does this !!
 
Originally Posted by brages
So... I'm starting to think that the old MAF is closer to reality than the new one is.

I needed a third car for today, so I decided to get the truck put back together and out of the garage. So first, I did a bit of tightening on the exhaust flange ahead of the O2 sensor. No change.

Then, I took off the upper intake manifold and replaced the intake side spark plugs (dual spark). Wow, they were worn! While I was there, I popped out the fuel injectors and took a peek at them and replaced the o-rings on them. Everything looked good on the injectors. Put it all back together with a new gasket. Cleaned the IACV while everything was off.

Then, I decided to replace the exhaust side plugs too, so I did that. They were just as bad. All Motorcraft, were they original at 265k miles? Who knows?

Put it all back together with the old MAF and when I started it up, I had +20 STFT and -20 LTFT and with time, they converged close to zero with STFT zigzagging back and forth. Looked pretty good to my inexperienced eye.

My old MAF shows about 3.2 g/sec at a 800 rpm idle. Not sure if that's high or what, but I took the truck to work (20+ miles) and it ran OK with no check engine lights. On the drive in, LTFT is running around -10. At idle, it tends to be closer to -5 and driving around, it's a bit up and down. Idle is OK initially at 1000 rpm, but after idling a couple of seconds, it settles down into the 750-800 range and you can feel quite a bit of vibration.

... so here's a little more back story...

I've had this thing about a year. The truck always had some vibrations at idle. A few months ago, the CEL came on with a P0172 (rich) code. I saw what I assumed were higher than correct air flow at idle and replaced the MAF at that time. The CEL went away for a while, then it started running rough and gave a P0303 (cylinder 3 misfire) code. I found that STFT was getting really high (+32) and causing the car to go into open loop, then in open loop it was misfiring. Revving the engine brought down the STFT and put it back into closed loop. I assumed the new MAF was the good one and started hunting for a vacuum leak...

With the new MAF, at idle, you can watch the O2 voltage and it just stays low (0.2V or whatever). It only spikes up if you give it gas.

With the old MAF, O2 voltage is swinging back and forth regularly. It takes about 3 seconds for a whole cycle. (seems slow to me)

I think I'm going to drive it as-is on the old MAF for a while and see if the P0172 pops up again...


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I had +20 STFT and -20 LTFT and with time, they converged close to zero with STFT zigzagging back and forth. Looked pretty good to my inexperienced eye
. .............. agreed
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On the drive in, LTFT is running around -10.
Dont think you can comment on that so soon at all - there are more than one LTFT figure as a function of throttle - you need to drive it quite a lot of hot and cold cycles for it to stabilize - I would say 10 is not necessarily the end of the world or even bad for the maintenance issues you described with plugs etc - its eventually an absolute function of the mechanical condition of the engine and historical maintenance schedules/quality
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O2 voltage is swinging back and forth regularly. It takes about 3 seconds for a whole cycle. (seems slow to me)
IMO its normal - engine speed increases sampling rate and also compensation rate..........

Chasing fuel trim issues with funky plugs is a waste of time .....................gonna guess the code is history by what you describe now - its obvious the ECU is in control of the animal if you have the animal well defined
 
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So I had the old MAF in and it continued to drive OK... Check engine light came on last week and it's a P1443... looks like a possible Evap valve. I checked the Evap valve and it's not sealing with power off, so that seems like it's bad. New one on order.

In OTHER news, I saw a code for a pending cyl 3 misfire AND something about a short in injector #3. So I'm thinking with my not holding fuel pressure that well, that I might have some kind of issue with injector #3.

Not sure if I should replace 'em all with remans or try to get what I have rebuilt or what... don't want to spend much on this truck.
 
Had a similar issue on my 02 Ranger with the 3.0L recently. My mechanic found that the MAF sensor had a bent terminal stab keeping it from making a good contact in the plug connector. It couldn't be straightened so he replaced it and the problem was gone. This was after troubleshooting for over a week.
 
I got a new evap purge valve from Amazon (SMP, made in USA - nice!)... while I was waiting for it to come in -- with the evap tubing removed -- my son drove the truck for ~50 miles. Came back with LTFT at +25 due to the giant vacuum leak.

Put the new purge valve in and seems to be working OK, LTFT in the +/- 5% range, jumps around a lot though, and CEL is off.

I ordered a set of "4 x Bosch UPGRADED 4 hole Fuel Injector for 1985-1997 Ford Ranger 2.3L" from eBay for cheap. Buyer feedback indicated they work: "Didnt look just like my old ones but tried anyway. Old girl runs great!" So we'll see.
 
Just found this thread and will hang with it to the bitter end.... '97 Ranger with the 4cyl Lima (5sp manual with about 235K) giving me fits. I can't say whether the issues are the same or even the same exact symptoms, but there's similar shi....tuff going on, I think.

Mine is symptomatic only until warmed up. It starts and idles fine, but if I don't let it warm up for a good 5-10min at idel, it will misfire badly and sometimes stall when I come off throttle. My misfire shows on cyl 1 (P0301), though I've seen other threads where it's other cylinders (including this one). If I let it warm up all the way, it does fine - symptomatically - but my OBDII data show that the underlying issue is still there: it will go super-lean at idle after I come off throttle. (STFT heads up into the 20s-30s for a bit). But - and this is what's so weird - at the same time the downstream O2 will peg rich (like .8v+). I know that the downstream is just to monitor the cat, but how could the upstream show super-lean while the downstream goes rich? IDK. Thinking an exhaust leak near the upstream, I unplugged to upstream O2 sensor to find no change in my symptoms .

Along with that, I've run the gamut. The coils, plugs, wires all done within the last couple years/20K miles mostly as a matter of course/maintenance. Fuel pump about 1 yr 10K miles ago - pressure was good but was cavitating (air bubbles). At this time I had also run compression - 175-180 across all cylinders (partially warm engine). Blocked off the EGR - no change. Blocked off the EVAP - no change. Sprayed all manner of propane and flammable liquids around intake points, including manifold to no avail. Pulled the intake snorkel and pulled and flexed and bent and etc. to look for hidden cracks. Can't find any. Cleaned the MAF (but also find no irregularities comparing TPS to load readings). Already did the Bosch 4 hole injectors to no avail. (Initial evidence pointed to a stuck open injector, so I, uh, I threw some parts at it. Intake gaskets at the same time since there's no other way to do the injectors). Checked the fuel pressure regulator and vacuum line for leaks. Nothing. Coolant and air temp sensors show nothing odd.

I had a vacuum gauge on it a couple of days ago. 19-20 inhg steady. Blipped the throttle and it started misfiring, but nothing dramatic showed on the vac gauge. A) I've seen the recessed valve seat stuff and if this was it, there would be some serious actions on the vac gauge every time cyl 1 came around and B) also some serious action if it was a temporary vacuum leak.

Um. What else? Feel free to ask because I'd love to know. I kind of feel like I know what I'm doing, but have reached the end of what I can figure out...
 
I just pulled by throttle body and IACV and found my IACV to be basically inoperable and hanging open by a little. The motor operates (you can hear it if voltage is applied and removed), but the plunger doesn't move. It's easy to move it back and forth (just using a little screwdriver), but always settles back to the same slightly open position.

This makes no sense as an explanation for my symptoms. First, this should be metered air so if it sticks open a little just make it idle high. Second, it always does the cold start routine just fine. It fires right up, goes to a fast/choke-on style idle and then slowly settles down. Third, I heated it up with a heatgun and this doesn't change its operation, whereas my symptoms disappear when the truck warms up.

But, in any case, I obviously need a new one so I'll throw one on and let people know what happens.
 
For what it's worth, my new injectors seemed to make no difference at all. Maybe a little peppier, but that's probably placebo.

It still does the weird thing where it starts and immediately dies, unless you leave the switch on for a couple of seconds.
 
Just to pile on. My 1998 ranger had lots of weird issues with the dpfe sensor. Aftermarket (napa/echlin) gave me fits. I ended up with oem. Also my connector was bad, I ended up cutting one off of a junkyard truck and soldering it on. My IAC also gave weird issues. It's super frustrating when aftermarket parts don't work, which seems to be the case more often nowadays.
 
Originally Posted by brages
It still does the weird thing where it starts and immediately dies, unless you leave the switch on for a couple of seconds.


I know that you said you cleaned your IACV, but I'm wondering whether you checked it in some way while it was off. If I had just the description above, it's the first thing I'd point to checking out. As I noted, mine was largely dead and I did have it off and cleaned it back when I did the injectors, but didn't check it in any way.

And I hope no one thinks I'm trying to "hijack" a thread by posting my own troubles. It was just that we have the same year/engine, many similar issues (though not identical), have done many of the same things to no avail, you and others here seems to know what they're talking about, and this thread is current (as opposed to the dead ones with no resolutions that you can find elsewhere). We could have completely different issues. But maybe not. So my intention was to just to exchange info as we chase our tails to see if our experiences help each other out.

So...that said, I'd encourage you to pull you IACV and check it, but replacing mine didn't do squat. Same symptoms. Still nothing is making sense. My IACV was the original and was not functioning. The pintle just floated independently of the motor. So I have no idea why my truck wasn't running worse than it was at idle. And even though I'm saying "check it" I can't say how to do that other than to see if it's easy to move the pintle shaft around.

My understanding has always been that an IACV is normally closed and opens fully when 12V is applied (for starting up). The PCM then pulses the ground to step it more/less closed. I've been in Escorts for longer than I care to say and that's how they work on an Escort. The IACV I bought today for the Ranger (unfortunately a Duralast from Autozone because it was what I could find today and I need the truck in the AM) was basically already open, and when I put 12V to it, it did nothing. But I know that the pintle shaft was solid and would not move (unlike my original). Having no other choice I shrugged and put it in. The basic start-up routine was normal - initial "choke-on" idle that settles down to a typical idle. So it's not obviously malfunctioning. But it didn't change my issues.
 
Originally Posted by Joe67
And I hope no one thinks I'm trying to "hijack" a thread by posting my own troubles. It was just that we have the same year/engine, many similar issues (though not identical), have done many of the same things to no avail, you and others here seems to know what they're talking about, and this thread is current (as opposed to the dead ones with no resolutions that you can find elsewhere). We could have completely different issues. But maybe not. So my intention was to just to exchange info as we chase our tails to see if our experiences help each other out.


Yep... same here. I am just using this thread as a way to post my experiences and listen to others weigh in if they wish.

The status on my Ranger right now is that it is perfectly functional and runs OK with no check engine lights. LTFT is in the +/- 5% range generally, so that's pretty normal. I think the gas mileage is acceptable and the power is fine. Oil stays very clean and it's not consuming much, if any. I have been running with the old MAF and haven't had any fuel trim related CELs. I did get a CEL for evap valve issues, but that was fixed by replacing the failed valve.

Here are the bad/weird things it does:

If you rev the engine really high, when it comes down to idle, it will idle very low and miss for a little while on one cylinder. This kind of sounds like the recessed valve seat issue. It's not an issue in normal driving, however.

If you turn the key to "on" and wait three seconds, it starts, revs up a bit, then settles down into an idle - fast idle if cold. If you immediately start the engine, it starts, revs up, then dies. If you restart, it starts normally.

There is some vibration at idle. If the A/C is cycling on and off, you feel extra vibration when the compressor kicks in and less when it disengages. This is annoying to me, but most people might not even notice.
 
Originally Posted by brages
If you rev the engine really high, when it comes down to idle, it will idle very low and miss for a little while on one cylinder. This kind of sounds like the recessed valve seat issue. It's not an issue in normal driving, however.


This is what mine is doing, and at this point will easily stall out. It goes super lean at that point, though the downstream O2 (if it's warm enough to operate) pegs rich. It's just weird. But this all goes away after it is fully warmed up. As such, mine is also perfectly functional...if I let it warm up a good 10 mins (which is often annoying).

Originally Posted by brages
If you turn the key to "on" and wait three seconds, it starts, revs up a bit, then settles down into an idle - fast idle if cold. If you immediately start the engine, it starts, revs up, then dies. If you restart, it starts normally.


My thought on asking about your IACV was that maybe it is basically sluggish/slow. Those 3 seconds might give it a chance to be where it belongs and it would be slow to respond when you come off revs and back down to idle too. Long shot, maybe, but at least it sits right up top for accessibility (unlike the PCV - what geniuses came up with that PCV location - on both ends?!)

The IACV is also supposed to get commands to open/close more based on loads for things like AC and power steering, so that also fits. Mine has no AC (never equipped) so I have nothing to compare there.
 
I have been deflecting the recessed valve seat issue because it didn't make sense. If the seats are recessed and messing with compression with a cold engine, it should just happen, and it should just run like sh** cold no matter what rather than doing fine is I just let it warm up. (Until everything got hot and expanded, I was presuming).

But I wasn't thinking through the potential effects of the hydraulic lifters with cold (i.e. thicker) oil, and the increased oil pressure with the high revs. I came across this thread: https://www.ranger-forums.com/sohc-...r-high-revs-runs-fine-above-idle-159246/ and was thinking both "aha" and "oh, shi....zzle"

I had also been thru this article already and went back to it: https://www.searchautoparts.com/mot...2s-analyze-intermittent-misfire-concerns

It's a pretty long and technical article, but in my case the bottom line is that if I had a true lean misfire (as my STFT does go superlean), then my downstream O2 would also go lean. But if I had a lack of ignition misfire (which could come from poor compression, though that's not in the article) then I very well might see lean upfront and rich in the rear - which I do. More aha and oh shizzle.

For the moment, my next "experiment" is going to be to Seafoam the crankcase for a while (see the ranger-forum thread on trying MMO). If this does chill out the symptoms (by thinning the oil) I'll groan again, but then also hope that it cleans the lifters to restore proper bleed-down? IDK, it's a great truck because it's cheap and easy and functional. But it started life in Minnesota and underbody rust is an issue so I doubt I'd bother with the head...It's last trip might be to the scrapyard if I get the worst case scenario.
 
Well, pretty sure I've verified that I'm at "oh, shizzle" with - probably - recessed exhaust valve seats, and that the reason it chills out once warmed up is just the thinner oil allowing the lifters to bleed down faster/more.

I vaguely recall hearing about the "dollar bill test" at some point in the past but found it again. It's generally said to be for finding burned exhaust valves, but same thing applies if its recessed seats. (And by now I likely have both...) You stick a dollar bill up to the tailpipe, and it should should just get pushed away steady. But if you have leaky exhaust valves, manifold vacuum will temporarily reverse flow whenever the valve doesn't seat so the bill will basically get sucked back toward the tailpipe and this makes it rattle against the pipe. (So IDK if you'd say that it mimics a vacuum leak, or just is one - sort of).

Anyway, the Ranger doesn't "pass." (I just used a slip of paper - same thing. It should be lightweight tho. I foil taped a flap of brown paper from a beer case and found what it did to be ambiguous). I have a few seconds of video from the Ranger and from a 97 Escort also with a 4 cyl SOHC (though a 2.0L). Having never done this before I just did the Escort for comparison and the difference was stark. I don't see a way to upload video here but you can find stuff on YouTube, obviously (though I never found one where someone shows exactly what it's supposed to look like if the valves are fine).

So, uh. I'd give the dollar bill test a whirl and see what you get.

I did add some SeaFoam to the crankcase and just plan to run with it for 500 miles or so and then change the oil. Hoping it'll clean up the lifters and buy me some more time with the truck. Probably not, but its a cheap try.
 
One time with my Chevy S10 4X4, I was stumped as to why my defrost and floor heat cycles didn't work, at any blower speed. All that worked was the bi-level setting.

Turns out there was a damaged hose right at / near the transfer case, underneath the vehicle. Once that was replaced, all my defroster, bi-level and floor heat settings began to work again.
 
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