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Have you taken a look at the fuel injectors yet?
Do you have a scan tool?
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.
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.
Let me know how it goes.
Does the connector at the PCM look ok?
I think the PCM is probably at fault.
Do those two cylinders fire at all or are they completely dead?
Yeah, there is probably a short in the PCM, especially since the problem is only on cylinder 3 and 4.
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.
A coil circuit code usually means the circuit is completely toast inside the PCM. Your original PCM is just partially failed.
Maybe you can find a reasonably priced re-man online.
That's not bad at all.
You bet. I hope that does it.
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.
Was the PCM programmed?
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.
How long have you run it since you swapped the PCM?
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.