MAP Sensor?

I just put a 4L in one of my XJs that came from a donor vehicle......it ran great before I pulled it. It now runs like it's hitting on 4 cyls and throwing 1-3 and 1-4 codes. Since this sensor ain't exactly cheap I thought I'd look for confirmation from you XJ gurus before I start throwing parts at it.

Gravely Tech said:

I just put a 4L in one of my XJs that came from a donor vehicle......it ran great before I pulled it. It now runs like it's hitting on 4 cyls and throwing 1-3 and 1-4 codes. Since this sensor ain't exactly cheap I thought I'd look for confirmation from you XJ gurus before I start throwing parts at it.

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What year stuff? The MAP sensor reads your vacuum, that's where your need to start, a code 13 14 don't mean the sensor is bad it only means that you should start trouble shooting there.

Running crappy after a swap, the first thing to check is firing order.

GTech, the code 13 is probably caused by the 14 code. 14 is MAP sensor input too high - OR too low. I'd look for a poor connection going to the MAP sensor. Check for a 5v reference voltage first with a voltmeter. If you have a black/lt blue wire going to it, check it with the key on.

I hate to admit this but.....mine was running like crap after removing hose from MAP. After a few ppl looked at it to make sure vacuum hose was on, my son noticed that hose was not actually on the fitting but on the screw that protruded from the bottom of the MAP(hey,I'm getting old). Put the hose on the fitting and all was well.

Thanks for admitting that! I have done more than a few "dumb" things like that and although I have bi focals, deep down I know they were not contributors to the real root problem!

Thanx for all of the replies, I'll check all suggested problem areas out when I get home from work today. Firing order should be OK, I didn't take the dist. out. Do I check ref voltage while the sensor is connected or at the pigtail? The patient is a `93 XJ.

GTech, I'd check the voltage with the plug connected. A good way to backprobe the wires is with a straight pin. Press the pin into the wire, and touch the pin with the multimeter probe. This prevents too much wire damage.

According to the wiring diagram I'm looking at, the MAP has three wires. The dark green/red is the signal wire. (I think) the purple/white is the 5v reference wire, and (I think) the black/lt blue is the ground.

Check both the purple/white and the black/lt blue for continuity with the engine block, with the key off. The wire with continuity to the block will be the ground. The other will be the 5v reference wire, which you can check for 5v with the key on.

These wires make connections to several other sensors. If you don't get a 5v reading on the MAP wire, check the plug-ins for the TPS, ECT, IAT, and VSS; they are all connected. Since this was an engine swap, I think the problem is a poor connection somewhere.....

Luck,
ROE