Help! 1994 4.0L Ranger misfiring & hesitating under load?

I have a 1994 Ranger, 2WD, 4.0L, 5-speed that has been gradually getting worse over the last few weeks.
The truck has 101k miles and it's pretty well maintained as far as tune-ups, oil changes, etc go.

Here is what i am dealing with: At idle, truck not moving - everything seems normal. RPM are stable, engine does not vibrate or shake more than usual. It feels the same as it did 3 years ago when i got it from previous owner.

The problem: When truck has not been driven for awhile, when accelerating or taking off from a stop, i can feel that the engine does not run smoothly and i can sense some roughness transmitted to the chassis. It feels like there is excessive engine vibration during slow or hard acceleration. What really bothers me is that as soon as i shift into second gear and i step on the gas (not floor it, but start to accelerate) i can feel that the truck is underpowered and that it starts to misfire, hesitate and even shake. It feels like it cuts on and off randomly.
If i happen to up-shift to 3rd gear a bit earlier and step on the gas, it misfires and SHAKES even worse and it feels extra sluggish! On 4th and 5th gear, this happens even more often and the shaking & misfiring are worse. Sometimes, i cannot even drive it on 5th when on the freeway because it shakes/misfires and it cannot accelerate to highway speeds and keep up. I am forced to keep it in 4th gear in order to do 65-70mph.

=> Another important symptom i noticed that is very disturbing is that sometimes, on 3rd gear or 4th, when i feel that truck is very underpowered and i floor it, it hesitates even more, shakes and i can hear & feel an audible"knock" or "detonation" somewhere seems like it's under my feet. Sometimes it does 2-3 or 4 detonations or audible "booms" in a row, until i back off from the gas.

=> The interesting thing is that once the truck warms up and has been driven for some time, the misfire, hesitations, shaking and overall sluggishness almost go away. It does not run perfectly but it is a lot better and smoother than it is when i drive it for the first few miles. It will still occasionally hesitate or misfire under hard acceleration. Unfortunately, over the last week, even when the truck warms up, it is still acting up.

So, what could be causing all this??

Here is what i have done so far to troubleshoot this with NO success:

1. Pulled OBD codes with OBD I Ford code scanner and only code i got is "214" which i've seen on and off for the last 3 years. I am 99% sure it is not related to this new misfire issue. Code 214 is Cylinder ID fault and i was never able to get rid of it. Again, i had this code 214 well before the misfire started. No other codes are stored in memory and the OBD I system seems very limited when it comes to diagnosis. It does not tell me which cylinder is misfiring.

2. I replaced all 6 spark plugs with properly gapped Autolite Platinum spark plugs. I installed new spark plug wires as well, few months ago. It made no difference.

3. I just replaced the coil pack with a brand new one (no brand name) that i got from Ebay. It made no difference compared the OEM one.

4. I got a spark tester and checked all 6 spark plugs for spark - all 6 tested good.

5. I cleaned the MAF sensor with MAF cleaner. It made no difference.

6. Air filter, PCV valve, and fuel filter are new. Made no difference.

7. Visually i do not see or hear any vacuum leaks, broken vacuum hoses, etc.

8. One of the oxygen sensors has been replaced in the past, since i see that it is branded Bosch and the other one is OEM Ford branded. I am not sure if a bad Oxygen sensor will cause such major misfire and/or detonations under load & acceleration.

9. This "problem" is gradually getting worse. The truck is driven very little since it is a third car and i use it only for weekend yard shopping trips. What started with minor hesitation and occasional misfire a year ago, is now happening 90-95% of the time. The truck is still drive-able and it starts every single time, does not die on me at stop lights and idles well. However, the loss of power is very obvious, the hesitation and misfires are common and the knocks/detonations are pretty loud under hard acceleration on 3rd/4th gear.

Given everything i listed above, what should i do next to diagnose and fix this?
Aside from the spark plugs and coil pack, what could be the next 2 or 3 most likely reasons for this problem? Injectors? Fuel pump? Catalytic converter? Bad MAF? Computer?

I cannot afford to buy brand new parts and try replacing everything on a truck that is worth $2k. This is why i want to start with the most likely areas first.


Thank you in advance for any input!
Dan

cut loose the converter and see if it change's or even stops, if not check and see if the time'n is off.

I agree with the cat and timing. It's possible it's getting or is clogged, but as it gets warmer it is not as bad. I would change the fuel filter as you are having a problem as the engine sees a load, the more load, the more hesitation and misfiring you have. Since you are not having a spark issue, it could be lack of fuel. I would also suspect a worn timing chain that has slack in it, changing the timing. Get/borrow a timing light if you don't have one, pull the pip (should be near the coil packs) and check timing at idle. Then check it at 2k. If its any more than 10* away from 0*tdc, I would pull the front cover and check the chain...
SVT

OK now I am new to ford rangers and this 4.0 OHV but I would be checkin the trigger at the harmonic balancer. I work on outboards and I have a 115hp johnson that did the same thing you just described and turned out to be the timing trigger. Just my 2 cents.

Another question i have is related to the CAMshaft position sensor.

I have been getting OBD I code #214 (Cylinder ID fault) for the last 2+ years but the truck seemed to run very well, despite the check engine light being always ON. I replaced the cranckshaft position sensor a year ago but it made no difference for the code. I still get 214. The only other sensor left that can cause this 214 code is the CAMshaft position sensor. My truck is 1994, and many Ford/Mazda documents state that 1994 should not have a camshaft sensor and only 1995+ have it.

My 1994 truck (built 11/93) HAS such sensor. I saw it and even took a picture of it. It's by the firewall and very hard to get to. It's a California truck, so maybe they put a 1995 4.0L engine in it. Who knows?!?! I am planning to buy a 1995 Camshaft position sensor and replace mine. I hope it fits since these things are not cheap.

As a side note, when i used my OBD I scanner and tried to run an "engine running" test to find mode codes, during the testing the OBD scanner tells you how many cylinders it is testing and it always shows "4" on my truck. I have a V6! Isn't this strange? Why is the scanner seeing only 4 cylinders on a V6 engine. Maybe that 214 code is the reason for it. Ideas?

Could a complete failure of the Camshaft position sensor be the reason for all my truck's misfiring, hesitation, engine vibration and loss of power??
My idle is still stable and the truck starts every time. It's only acting up under ANY acceleration and load. It's is getting worse by the day.

At this point i am leaning towards: a) bad Camshaft sensor, b) bad Catalytic converters, c) Bad Fuel pump or injector. Am i missing anything else more obvious?

Thanks!
Dan

What about fuel pressure regulator?

Dan

I tested the fuel pressure today, using a new fuel pressure gauge i bought.
Here are my numbers, let me know if they seem low and out of spec.

Ignition ON, Engine not running - 38 psi
Engine running, @ Idle - 31 psi
Engine running, RPM at 2500-3000 - 29 psi

The only time i got above 35psi was when the engine was OFF and the ignition was ON.

My fuel filter is less than 1000 miles old.

Are the 31psi and 29psi numbers major reason for concern and are they a SURE sign that i need to replace the fuel pump??

I would suspect the CPS with the new info, small possibility of the ECU as well. It is timing related, that I can tell you as the problem gets worse with the increase in load...
SVT

RangerSVT said:

...It is timing related, that I can tell you as the problem gets worse with the increase in load...
SVT

Click to expand...

So, you don't suspect that the cats may be clogged and causing all this behavior, under load? What symptoms will a bad catalytic converter show?
My truck starts every time and idles well, but other than that, it does not run well. I now feel hesitation on 1st gear, 2nd too and it gets very bad on 3rd & 4th. It's getting worse.

What about bad/clogged injector? Good fuel pressure at the rail does not guarantee me working fuel injectors, does it? Or will a bad injector cause different issues??

I am just brainstorming here, not dismissing your comment and suggestions at all.

Thanks!

From your numbers on pressure you posted above, I would suspect fuel pump issues. Idle pressure seems to be fine, but under load (when pump works the hardest) your pressure should be up near 40 psi....not less than when idling. Have you checked for vacuum leaks around fuel pressure regulator, which could cause some similar issues under load not allowing the full pressure to build?

Dan

bigdan002001 said:

From your numbers on pressure you posted above, I would suspect fuel pump issues. Idle pressure seems to be fine, but under load (when pump works the hardest) your pressure should be up near 40 psi....not less than when idling. Have you checked for vacuum leaks around fuel pressure regulator, which could cause some similar issues under load not allowing the full pressure to build?

Dan

Click to expand...

I was thinking this as well. More tests are needed to be done of course. The cats could be a problem, but it could also be other issues leading to cat faliure. How many miles are on it?? When you give it 3/4 or more throttle, do you see any black smoke exit the tail pipe?? If you do, there is a good chance the cats are clogged.

Take and hook up a fuel pressure gauge while you drive the truck. Low pressure while at 2K and no load will differ from 2K and a load. IIRC, fuel pressure should be around 50-60 psi engine off, key on, and around 35-40 psi engine running...
SVT

The fuel pressue sounds fine to me....

- How many cycles of the key did it take to get to 38 @ koeo

-the koer pressure should be around 30 it should go up about 10 psi when you pull the vacuum line off the regulator

-the psi should not drop more than about 8 within 5 minutes of turning the truck off

-I would try the unplug and run method.......pull the maf connection off when the truck is acting up....pull the ect connection off and see what happens

modelageek said:

-I would try the unplug and run method.......pull the maf connection off when the truck is acting up....pull the ect connection off and see what happens

Click to expand...

This works on Government Motors (GM), not Ford. GM's use an off/on signal, while uses variable voltage. If the ECU sees no voltage return, it could shut the system down, or not start at all. To test the system correctly, you need to run a scantool on it.
SVT

I am gonna go on a limb here, Are you the only owner of this rig Danmm7?
Have you looked to see if the ECU is the correct ECU for the engine you have?
Just trying the process of elimination..

SRV would cats clogging throw a code 214? I don't find any literature on this specific code relating to cats.

my truck is doing the same thing. replaced everything you replaced plus fuel pump and regulator. new maf, fuel filter, plugs and wires, o2 sensor ( only 1 was bad), checked coil, i'm changing the ecu tomorrow maybe if i have time. if this fixes mine i will let u know. note mine shows random codes everytime i put the scantool on it, mostly maf high or low voltage, replaced the maf twice and checked all wiring, still in the process of elimination lol gets expensive