I retired from this business in 86 about when they started going nuts
with emission requirements. After dealing with these shops I figured
I'll take a stab at it myself so I bought an OBDII scanner and am
learning to use the data supplied by the onboard computer.


I've been fighting this problem for a month. The truck has been to the
shop 3 times and still has problems with dying at stop signs,
hesitation, and what feels like a miss at any speed hot or cold, and
sometimes shudders when coming to a stop. It backfires thorugh the intake mainly when cold and stumbles when hot. The truck 96 ranger 3.0 single
overhead cam with 61000 miles. The parts I have replaced are as
follows:
fuel filter
ect sensor
plugs
wires
maf
tps
egr
pcv
fuel pressure ok
vacuum ok
one upstream o2 sensor (bank 2) today which is operating in specs now.
According to the scanner the o2 voltage on the sensors are almost
running together indicating a bad cat on the #2 bank and the #1 is
starting to look bad. Lately it put out the old rotten egg smell which
usually indicates rich fuel. The #2 bank was rich and the new sensor
took care of that. Since both cats are looking bad I can't hardly
belive the fuel injectors are at fault. I did a back pressure test and it's only 1/2 psi. I haven't been using oil or
water which would foul the cats. I unplugged the cam sensor and no change. It starts up no problem kind of eliminates the crank sensor. I can't put on new cats until I find the cause of the rich fuel mixture. Any ideas would be appreciated. Thanks

 

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Welcome to FTE!

Is the computer storing any diagnostic trouble codes, if so, what are they?

Idle concerns are usually air-related (too much or not enough) which is why the Idle Air Control (IAC) valve is always at the top of the list of possible suspects. Among other things, it controls air flow during all closed-throttle situations, including deceleration. You don't indicate that you have tested or replaced it.

However, it sounds to me like your truck may have a bit more than an idle issue. Have you had a compression test done on all the cylinders?

Plugged up cats can cause a host of driveability issues, you might look at it from that perspective, too.

 

Thanks for your quick response.

I had a P0430 catalyst efficiency below threshhold bank #2 about a month ago. I cleared it and it never came back. As far as the IAC I inspected it and it was not froze just a little carbon. I have not done a compression test yet but will. I did a back pressure test on the exhaust. I only have about a 1/2 psi. I pulled the new o2 sensor for this test it was blackened with carbon the #1 side was o.k. I was looking for the cause of the rich fuel mixture on bank #2 before I change the cats they are not cheap don't want to foul the new ones.
At idle when I snap the throttle the engine bogs down then sometimes backfires through the intake. The backfire is mainly when it's cold but it has done it at operating temp.

I also checked the voltage of the CMP I get 7.3 VAC with little change as RPMs increase. I don't know if this is good or bad. I understand the CMP only locates the #1 cylinder during start-up. I have no starting problems at all. Got me stumped.

 

Have you checked the distributor cap and rotor? Just a thought.

Ron

 

It's computer controlled.

 

OOPs! Dah,...sorry bout that.

Then the module might be bad or going bad.

Ron

 

All electrical has been checked and re-checked. Tonight I am pulling the injectors for test and clean. I left this as my last option something I really didn't want to do.

 

I'm not familiar with working on the distributorless ignition system, but as I read my Chilton (not the best source for troubleshooting) it seems that the crankshaft position sensor (CKP) and camshaft position sensor (CMP) work in concert with the PCM (power control module or computer) and the ICM (ignition control module) to control ignition spark at the proper timing. A note in the Chilton's indicates that "on the 96-97 models, the PCM performs the ICM tasks." The 96 and on models do not seem to have an ICM and all tasks are performed by the PCM.

Apparently, the CKP and CMP take the place of the hall effect device used in the older systems with a distributor.

The PCM receives IGN, GND, and PIP signals from the ICM, then generates a SPOUT signal based upon engine speed, load, temperature and other sensor information.

The coil pack is turned on by the ICM. then turned off, thus firing two spark plugs at once. One is for the cylinder which is to be fired (on compression stroke) and the other is the mating cylinder which is on the exhaust stroke.

As I understand this, then if you have an open or sticking fuel injector that is allowing fuel to enter the cylinder on it's exhaust stroke, this could be the cause of your backfire. I don't know that this would cause it to die at stop signs, but it would definitely run rough. If your injectors all prove to be OK, then I'd suspect the PCM as the problem.

BTW, you haven't mentioned anything about the crankshaft position sensor (CKP)

Just a thought.

Ron

 

Both CMP and CKP are working ok in accordance with Chiltons and my OBD II scanner. I'll know this evening when I reinstall the injectors. I'll post my findings.

 

The motor had the wrong injectors installed at the factory. The pintle caps had a 39mm orfice the correct size should be 21mm according to pro-flow injector service. I have full power no hesitation or backfire. I still have a stumble at 50mph. I am going to look at the coil a little closer. Thank everyone for their input. Will update when I figure out this stumble. Ideas are still welcome.

 

Good to hear you're making progress. Sounds to me like it's not the original 3.0L "vulcan" engine in your '96 Ranger. I say this because many of the later 3.0L vulcans are actually "flex-fuel" capable, meaning that they can run on E85 fuel. Aside from some differences in the vehicles' fuel delivery system (different fuel pump, fuel filter, alcohol % sensor, etc.), they employ identical engines; however, one of those differences also involves larger fuel injectors for the FFVs.

Other than someone replacing all of the original factory injectors and choosing the wrong ones, it seems to me the most reasonable explanation is a transplanted engine. I've read several posts wherein other people have described running into the same issue.

As for the miss, you didn't use Bosch spark plugs when you replaced them, did you?

 

No I used Autolite double platinum. I bought it brand spankin new. Who knows how the injectors were mixed uo, maybe it was built late on a friday afternoon.

 

The motor is running like new except for that occasional stutter at highway speeds. I read the trans could give these same symptoms due to dirty filter or speed sensor anyone ever expierenced this symptom asscoiated with the trans?