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Jared D
Jared D, ASE Certified Technician
Category: Ford
Satisfied Customers: 1334
Experience:  Shop Supervisor at County Fleet
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96 ford explorer 4.0l cyl. 3-4 misfire. Put new plugs wires

Customer Question

96 ford explorer 4.0l cyl. 3-4 misfire. Put new plugs wires coil pack intake manifold set egr tube o ring cleaned IAC. At a loss to what to do next any help would be appreciated
Submitted: 1 year ago.
Category: Ford
Expert:  Jared D replied 1 year ago.

Have you taken a look at the fuel injectors yet?

Do you have a scan tool?

Customer: replied 1 year ago.
sry forgot to mention that I ohms tested the injectors and used a noid light on the wiring and it flashed on every one
Customer: replied 1 year ago.
its just a Bosch from O'Reillys not much live data
Expert:  Jared D replied 1 year ago.

If you can pull fuel trims check the following:

1. Monitor the long term fuel trims, if fuel trims are high (over 10%) at idle only, but come down off idle, suspect vacuum leak. Use short term fuel trims while spraying carburetor spray around all intake areas, if fuel trims drop into negative numbers in any particular area, suspect that area as a leak. On this particular vehicle, pay special attention around the upper intake gaskets and exhaust gas recirculation tube.

2. If fuel trims are fine at idle, but are excessively high during acceleration or cruising speeds, suspect fuel concern, or mass air flow input concern.

3. Check fuel pressure during the concern, if fuel pressure drops below 30 PSI during low power concern. Check power and ground to the fuel pump during the concern. If no power or ground is lost during low fuel pressure, suspect plugged fuel filter or weak pump.

4. If the fuel pressure does not drop during a lack of power or high fuel trim event, first check the mass air flow voltage. In most cases, normal voltage will be .6 to .9 volts at idle. Compare mass air flow voltages to specification. In most cases, if the mass air flow is the cause of the lean condition, unplugging the mass air flow sensor and road testing can be an effective means of diagnosing. If concern is still present with the mass air flow sensor unplugged, it is unlikely the mass air flow sensor is the cause.

5. If fuel pressure, mass air flow voltage is ok, and there are no vacuum leaks, suspect fuel quality concern or possible plugged injectors.

Customer: replied 1 year ago.
Long term is at 0 I retried the spraying around the intake test it doesn't change anything I'll need to get my fuel pressure gauge to test the fuel pressure but seems strange that blow fuel pressure would only chase the number 3-4 cylinders only . don't the 3-4 cyl share the coil on the coil pack?
Expert:  Jared D replied 1 year ago.

They are fired at the same time by the same driver circuit. You replaced the coils though right?

Check the coil driver circuit, for cylinders 3 and 4, from the Powertrain Control Module (PCM) pin 52 to the coil Tan/Orange (TN/OG).

Inspect the coil and PCM pins and connectors for damage. If all the above is OK, replace the PCM.

Customer: replied 1 year ago.
Ok I'll try to test the driver circuit and to check the connectors for any issues
Expert:  Jared D replied 1 year ago.

Let me know how it goes.

Customer: replied 1 year ago.
Ok I have continuity on the pin 52 to the coil pack but the wire color I had was yellow with red tracer
Expert:  Jared D replied 1 year ago.

Does the connector at the PCM look ok?

Customer: replied 1 year ago.
looks good
Expert:  Jared D replied 1 year ago.

I think the PCM is probably at fault.

Expert:  Jared D replied 1 year ago.

Do those two cylinders fire at all or are they completely dead?

Customer: replied 1 year ago.
It fires on both cylinders but runs like a dead miss
Expert:  Jared D replied 1 year ago.

Yeah, there is probably a short in the PCM, especially since the problem is only on cylinder 3 and 4.

Customer: replied 1 year ago.
Ok do these pcms need programmed like if I get one out of another truck or should I buy new
Expert:  Jared D replied 1 year ago.

You could probably get and used model to start and run without programming, but to get it to run right you will need to have the dealer flash it.

Customer: replied 1 year ago.
Ok well I did get another PCM out of a junkyard and tried it in it but it threw a coil sec circuit code instantly and it won't run stay running unless I hold the throttle some
Customer: replied 1 year ago.
I think it's another bad PCM to tell u the truth so I just took it out and reinstalled the old one
Expert:  Jared D replied 1 year ago.

A coil circuit code usually means the circuit is completely toast inside the PCM. Your original PCM is just partially failed.

Customer: replied 1 year ago.
OK I'll prolly just have em buy a new one then
Expert:  Jared D replied 1 year ago.

Maybe you can find a reasonably priced re-man online.

Customer: replied 1 year ago.
Ya I found one on EBay reman for 161 with lifetime warranty
Expert:  Jared D replied 1 year ago.

That's not bad at all.

Customer: replied 1 year ago.
Nope but I'll get it ordered and then let u know wat it does thank u
Expert:  Jared D replied 1 year ago.

You bet. I hope that does it.

Expert:  Jared D replied 1 year ago.

Let me know if you need any more help.

Please don't forget to rate. They don't pay us if we don't get a positive rating.

Customer: replied 1 year ago.
I will def let u know still waiting for new pcm
Expert:  Jared D replied 1 year ago.

Ok, great.

Customer: replied 1 year ago.
Got the PCM installed which was a used PCM from a computer rebuild place near here and the explorer still runs like crap I test drove for three or four miles and no light yet so I have no codes to report yet but ik its not going to be long before it comes back on
Expert:  Jared D replied 1 year ago.

Was the PCM programmed?

Customer: replied 1 year ago.
Didn't think that year needed programmed
Expert:  Jared D replied 1 year ago.

They use the same PCM in multiple vehicles. If that PCM came out of a 4.0l then it should be fine, but it could be from a number of vehicles with different engine options.

Customer: replied 1 year ago.
This one by part number shows only 4.0l so should be ok
Customer: replied 1 year ago.
This is at idle
Customer: replied 1 year ago.
I also sprayed around any vacuum line and intake nothing changes on the Lt fuel trm
Expert:  Jared D replied 1 year ago.

How long have you run it since you swapped the PCM?

Customer: replied 1 year ago.
Been running for close to an hour now
Customer: replied 1 year ago.
Codes came back cyl3 and cyl4 misfire again
Customer: replied 12 months ago.
Any ideas sir
Expert:  Jared D replied 12 months ago.

Sorry, we are having internet troubles here at the shop. We were down for the last two days.

I am a little stumped on this one. It's really weird that only 3 and 4 are missing, especially since you have changed everything that runs them.

Let me look over the diagrams a little more and see if I can come up with something.

Customer: replied 12 months ago.
Ok that's no problem and thank you im stumped also lol
Customer: replied 11 months ago.
Have u had a chance to figure anything out