97 Ranger, emissions readiness problem
 

Hey guys, i have a 97 ranger with 169k miles on it i bought a couple weeks ago..i live in GA and they require emissions in the county where i am...i took it in and it failed for readiness, almost all the monitors were "not ready"..the guy i bought it from told me he put a brand new batt in a couple days before i got it so i drove it around a week or and brought it back for emissions, everything was ready!

So they did the test, failed again, everything went right back to not ready...so again i drove it around, another 100 miles or so, everything back to ready...heres the problem, when we do the test, he plugs up the odbii plug, reads it, everything is ready, shut the engine off, gotta wait 20 sec, start back up it all goes back to not ready...what could be restting these monitors just by on/off at the ignition switch? is it a bad ign switch, odbii connector, some kind of fuse or relay or bad computer in the truck? really need help guys, i dunno what to look for.. down to my last days to get this truck to pass or i wont be able to drive it/register it...thx! great forum here.

why don't you try a different testing station and see if it does the same thing...
obviously something is making the computer reset. could be power is cut to it maybe?
also it shouldn't take a 100 miles to get the sensors to be 'ready'.

x2.. I had the same thing happen and it fixed itself..never had the problem again lol. Maybe the ranger gods like me.

yes going to try another station this wknd

Have you had the system scanned for any stored codes? If you can get hold of a scanner (local Auto parts store) simulate the event and see what comes up on the scanner after restarting.

Here are a couple of links that may help with the I/M Readiness Code

Link 1 Ref Page 50

Link 2

Link 3

No i havent..there has never been a check engine light on i know that, dont know if that applies to what youre asking tho sorry..

Heres a new twist, i noticed the other day that this truck would start and run with no key in it! so i got a new ign lock cylinder from autozone and put that in today, unfortunately i had to disco the batt so have to start from scratch here..anyway, there was a little black ground with what looked like a pressure tab that rests against the lock cylinder that wasnt even in there, so i put that in properly on the new one...

Now the cylinder turns correctly and key only comes out in off position where it was coming out at all different positions before so im not really even sure i was shutting this truck off right before....also no longer does the chime go crazy whenever i open the drivers door, but only when the door is open and the key is in the ignition, i take it thats normal now.

I'd stop by one of the local auto parts stores and see if they can scan the system for you.

Also, if you haven't already done so, you might want to check all fuses, especially fuse # 5 (15amp) in the power distribution box under hood. Also, make sure that fuse has power even with the key off.

For a pictorial of the fuse location, click this link and go to page 224 of the owners manual Click Link

Excellent, thx for the inside info, this is the kinda stuff i was lookin for, thx Rev

No problem...If you get the codes scanned, if any, post them up and someone should be able to point you in the right direction.

ok Rev, that fuse was popped! just tried to replace it and when i do, it automatically pops...no matter what size fuse i put in there, i tried a couple higher rated fuses just to see and they pop...so obviously this is my problem...so does this mean a wire on the pcm is grounded that shouldnt be? any tips on troubleshooting this?

i read your comments here: https://www.ranger-forums.com/general-technical-electrical-18/pcm-fuse-keeps-blowing-90068/

i removed the pcm power relay and the fuse still pops immediately, arrrgh!

It sounds like you have a short to ground in one of the engine wiring harness. The wire in question is a yellow wire coming from fuse 5 in the Power Distribution Box (PDB) to terminal 55 on the PCM. You’ll need to trace this wire (harness) from the PDB to the PCM (located on the right hand side of the engine compartment on the firewall just above the blower motor). I Believe the harness in question runs along the back side of the engine. Do a thorough visual inspection of the engine harness.

This fuse supplies power directly to the PCM keep alive memory terminal 55. The PCM power relay is on different circuit.

ok so the big bundle(s) going from underneath the PDB to the PCM itself, find the yellow wire coming off fuse 5 and find out where its touching metal, correct?

I'd start at the PCM and work back towards the PDB. More than likely its simply pinch somewhere along that harness. Look for any signs of damage to the harness...Squashed, cut, ripped, etc.

Cool, gonna get started.

In worst case scenario, to locate a short, hook a 12v 5-10 amp automatic reset Circuit Breaker in place of the fuse. Using a compass, slowly move it along with wiring harness. You’ll see the needle swing every time the breaker opens and closes. Once you go past the short, the compass needle will stop swinging, indicating the point of the short.

ok rev thx for suggestion Rev...hey question, is that yellow wire/#5 fuse an isolated circuit? I was wondering if i could just cut the yellow wire coming from terminal 55 and cut it at the PDB and re-splice a new wire and bypass the harness?

Based on the wiring schematics it appears to be a dedicated circuit to the PCM Memory. I guess you could bypass it. However, there may be more than just this one wire damaged in the harness. I'd make every effort to find the problem first before considering bypassing this wire. .

understood, problem is, im on a time limit to get this thing thru another drive cycle and pass emissions, afterwards i would surely fix it properly and get it right, im usually a perfectionist with projects, just dont have the time and its raining!

It’s your call…But if time is of the essences and there are other damaged wires that may effect the PCM or other sensors proper operation, you may not know until your sitting at the smog station and find your truck has failed again due to some other cause.

A very thorough hands on visual inspection (inch by inch with a good light and twisting the harness to see the back side) should produce the culprit.

Once this wiring issue is fixed it shouldn’t take more than 24 hours of driving for the system to go through its paces and reset the system.

Yep thx rev and you are right in doing it the right way the 1st time...question, besides it clearing the codes each time, every time ive tested it (3 times) its passed everything, as far as the emissions themselves go, just the readiness fails...so do u still think once it starts storing the memory it could fail again?

If other wires are effected, yes you may still have further problems to deal with.

From the pictures I've been able to find it appears the PCM wiring harness dips below the EGR along the firewall and comes back up to the PDB by the brake booster. Concentrate your visual inspection from the center line of the engine following the harness below the EGR valve to the PDB.

I'd suspect that either the EGR valve tube may have melted the harness or someone may have had the transmission out and may have pinched the harness while re-installing it.

Ok so i got the PCM memory fuse fixed, and its definitely retaining the codes now because i put about 40 miles on the truck, fuse is still good and on comes the check engine light...ugh

So i took it to autozone, they scanned the code and it gave "P0420"...after he printed out the explanation for me, it seems its either the catalytic converter, sensors #2, #3 and #4 or a vacuum leak, or an oil leak or an engine misfire...

All i can say about how it runs is that the truck does sound like it has a "leaky exhaust" is how ive always put it...and when i 1st start it in the morning some water comes out of the tailpipe, followed by a little steam til it warms up, no water in the oil or anything like that.

So any ideas on where to start here rev? for whatever its worth, as soon as the guy at autozone saw the code he immediately said it needed a new catalytic converter.

i would clear the code then take the truck and do a really good italian tuneup and
then see if that code or others show up.

So where was the short or did you by-pass the circuit?

P0420 OBD-II Trouble Code What does that mean?

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Symptoms:

You will likely not notice any drivability problems, although there may be symptoms.

Causes:

A code P0420 may mean that one or more of the following has happened:

An oxygen sensor is not reading (functioning) properly.
The oxygen sensors in front and behind the converter are reporting too similar of readings (catalytic converter is not functioning properly).
Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe.
The engine coolant temperature sensor is not working properly.
Retarded spark timing.
Leaded fuel was used where unleaded was called for.

For a leak in the exhaust to cause this problem it would be very noticeable. As far as the water dripping from the tail pipe and or near the muffler, this is normal when you first start up cold. If it continues after reaching normal operating temp, then I'd be concerned.