map testing results

Trying to diagnose a pretty good hesitation on my 88 4.0. One of the things I looked at was the map sensor. Ran a test on it today and got the following results: 4.8 volts with the key on input and output, 2.3 volts with the engine running. The reference material I have say the spec for the voltage with the engine running is .5 - 1.5 volts. My buddy, who I bought jeep from, said that when the map sensor was replace it was done so because it showed 1.5 volts, which he was told was out of spec. Anyone tell me what the correct spec is? It only has about 9k miles and 2.5 years on it which makes me wonder why it would go so quick if it is in fact bad.

From alldata.

1. Turn the ignition switch ON (the engine should remain off), and test the voltage from connector terminal B to ground with a voltmeter. Voltage should be between 4 to 5 volts. With the engine started, warmed to normal operating temperature, and idling, the voltage output should drop to 1.5 to 2.1 volts.
2. Check for voltage at ECU electrical terminal C-6 in the same way as in step 1. The voltage readings should be the same as in step 1. If the voltages are different, then the wiring harness should be suspected as the problem area.
3. Check the supply voltage to the sensor by connecting a voltmeter to connector terminal C and a ground. Voltage reading should be 5 +/- 0.5 volts with the ignition switch ON. There should also be 5 +/- 0.5 volts at ECU electrical terminal C-14. Repair wiring harness if necessary.
4. Check the sensor ground circuit between electrical terminal A on the sensor and ECU connector terminal D-3. Connect one lead of an ohmmeter to electrical terminal A of the sensor and the other to ECU connector terminal D-3. The ohmmeter should indicate continuity. Repair wiring harness if necessary.
5. Check the sensor ground circuit at the ECU electrical connector. Connect an ohmmeter between terminals D-3 and B-11 of the ECU electrical connector. If the ohmmeter does not indicate continuity, check the sensor ground connection at the right side of the engine block at the oil dipstick mounting stud. If the ground connection is good, replace the ECU.

First thing to do on that 88 is to refresh all your engine bay grounds. Start with the firewall on the driver side, back of the head. Then, all the ones on the engine dipstick tube stud. Don't just look at them. Remove, clean, scrape til shiny. These grounds are super critical to the proper operation of your fuel injection system.

Thanks guys. The grounds were replaced by the previous owner about 3-4 yrs ago, so I didn't think about checking them. Guess it wouldn't be a bad idea to do so though, and would be an easy check.

On top of that, it never hurts to unplug, clean, and spray out every engine management/sensor connector just for the hell of it.

A bad EGR transducer can cause serious stumbling off idle. Can cause EGR to open when it should be closed.

So, after a bunch of research and testing of the different sensors under the hood I finally broke down and dropped her off down the street last night to get it looked at. They came back saying it is the fuel pump, which I had tested the other day and though was actually ok. They said that it shows ok on idle, but not when there is a load applied to it, which is a condition that I didn't check. They wanted about $425 to place it and the filter. So anyone wanna guess what I'm doing this weekend?

Fuel Flow Test by DJ

I would start with the easy check first by crawling under the left hand side (facing the rear of the Jeep) just forward of the rear tire then look up in the body hump for the fuel filter.

When fuel filter is located remove the rubber hose between fuel tank and the filter, extend this hose with additional hose into some sort of container and secure this hose to the container.

Next turn the ignition switch to the on position wait for fuel pump to complete its priming cycle, turn off switch then look in the container for a realist amount of fuel. If realist amount is noted reconnect supply hose remove discharge hose from fuel filter and repeat test.

If small of fuel is noted on either test you are on the right track to correcting fuel delivery problem.

There is also a filter sock on the intake of the fuel pump.

And a rubber hose connected to the fuel pump inside the tank that has been going soft on some XJ which will deplete fuel flow.

Or the fuel pump may have become dislodged from its cradle and may be floating on top of the fuel.
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87-90 fuel pumps problem Renix by Ecomike
http://www.naxja.org/forum/showthread.php?t=1048534
I had a non working fuel pump about 18 months ago, 20,000 miles ago on my 87 XJ Wagoneer. I cleaned the fuel pump QC male/female connectors and ground/external connection at the rear of the face plate on the outer housing and the fuel pump has worked ever since. 2 weeks ago the same thing happened to my daughter's 89 XJ. I cleaned the same connectors on it and that fuel has worked ever since.
Most people would have replaced the fuel pumps. I think it may partly be a grounding issue over time.
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Grimm Jeeper posted I just swapped out my a Renix pump I was sure was bad, even though I could hear it working the truck would die every time I touched the gas pedal and would barely idle. Turns out the feed hose was rotted out inside the tank (from the pump to the hard-line that passes through the plate). Next time I'm starting with the fuel pump instead of swapping in all my spare sensors and such.
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Mike, the key when doing the shoot it out test is to look for air bubbles, I bet that steady stream had air in it too.

That hose is one of the first things I suspect when I have problems that feel like starvation and I can still hear the pump going. I haven't had the problem with grounding but then I live in California, I'm spoiled
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87XJ fuel pump replacement
http://www.allpar.com/SUVs/jeep/fuel-pump.html
My 1987 Jeep (XJ) became victim to a dead fuel pump over the weekend. Here is a replacement how-to for Renix era XJs.
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Post back what you discover.

Fuel pump did the trick. Thanks again for all the input.