Replaced fuel pump still having the same problems

Nope. That is an issue with the fuel level sending unit. It will read correctly at most levels, but most commonly it drops to "Empty" when the tank is between 1/4 and 1/2 full. If you replaced the entire fuel pump and housing assembly, that comes with a new sending unit which would have solved the problem.

If you replaced just the pump and motor that had to be installed into the old housing, the sending unit would have been reused. The better repair then is to remove the clip that holds the float arm on, bend the metal tabs a little so they make better contact with the sending unit element, then pop it back on. That quick repair is more effective than replacing the sending unit which is likely to develop the same problem in a few years.

You said you replaced the fuel pump, but there are two ways to do that. You can put a new pump and motor into the housing, or you can buy the complete housing with the motor already in it. The complete housing comes with a new sending unit. The less expensive pump-only does not come with a new sending unit.

The sending unit is the fuel level sensor in the tank. It has the float arm hanging on it that you saw when you pulled the assembly out of the tank. The electrical contact has one or two small spring-metal tabs for the electrical contacts. Those are what needs to be bent just a little so they make better contact. When they make a bad contact, the fuel level gauge will drop to "empty".

Idle speed is controlled by the engine computer. It is supposed to run it up to 1500 rpm for a few seconds when you start the engine, then it will come back down to around 800 rpm.

To understand how to approach an incorrect idle speed, it helps to explain how the system works. There is an idle speed motor that opens or closes a valve as it slowly rotates. That valve controls how much air is going into the engine. The computer places it at the desired position by pulsing its internal electromagnetic coils with varying voltages and polarities. Those positions are called "steps", and there are 256 of them. The higher the step number selected, the more air is going into the engine. At the same time, the computer adjusts how many milliseconds it pulses the injectors open to allow gas into the engine. Slightly longer pulses along with higher idle speed motor steps equals a higher idle speed.

For explaining how we diagnose this, understanding the idle steps is what is important. Those steps are displayed on a scanner. For a properly-running engine, you will typically find it on around step 32. If one cylinder is misfiring, you will find it at around step 50. For demonstration purposes, if six cylinders are disabled on a V-8 engine, it will obviously run very poorly, but the computer has enough control to keep it running at the correct idle speed with only those last two cylinders working. It will be at around step 200.

Now the issue is what is happening when idle speed is not correct. When it is too high, we need to look at the idle steps on a scanner to see what the computer is trying to do. If you see the idle steps are real low, (remember, for this sad story, step 32 is normal), as in step 0 to around step 10, the computer is trying to lower engine speed, but without success. This is almost always caused by a vacuum leak. Cracked and dry-rotted hoses are the best suspects. We find those by pinching them off, then observing if engine speed drops. Sometimes pouring water over the engine when it is still cold will work. Watch for where the water gets sucked in.

If the idle step number is higher than normal, say step 40 to 60, the computer is trying to raise idle speed. If it should not be doing that, we have to look at the rest of the sensor data on the scanner to see what it is responding to. The most important variables are coolant temperature and intake air temperature. Years ago we needed a choke when the engine was cold. That is because less than 100 percent of the gas vaporized in cold weather, and gas that remains a liquid will not burn. We had to dump in extra gas so enough of it would burn to make the engine run right. Today, with fuel injection, a higher percentage of the gas vaporizes properly, but still not all of it when the engine is cold. We still have to add a little extra for the first few minutes until the engine warms up. That is where the computer watches the readings from the coolant and air temperature sensors.

It is our job to see if the readings from those two sensors look reasonable. For example, if it is 40 degrees outside, that is what the intake air temperature sensor had better be reading. The coolant temperature sensor should be reading the same when the engine is first started, but that reading must gradually rise smoothly as the engine warms up. If the two sensors do not agree when the engine is still cold, that is a dandy clue. You have to figure out which one is wrong.

One important tidbit is temperature sensors have an extremely low failure rate because there is just one component inside them. By far more problems are caused by the wiring going to those sensors, and especially the connector terminals. Corrosion between mating terminals in a connector will add resistance which makes the signal voltage go too high. The computer interprets a higher voltage as a lower temperature, and a lower temperature calls for a higher idle speed.

You are at a big disadvantage when you do not have a scanner. You will not know what the computer is seeing or trying to do. The only thing you can do then is search for a vacuum leak. Look for vacuum hoses you can pinch while the engine is running and the idle speed is too high. Start with the largest ones or those closest to the engine. If engine speed suddenly drops a lot when you pinch a hose, follow that hose to where it branches off, then pinch each branch hose to see which one makes engine speed drop. Following hoses this way often leads us to the leak.

I am in the middle, (north central) of Wisconsin. I have a Chrysler DRB3 scanner for all of my vehicles, but the cables will not reach to your Jeep! You can find these on eBay. Mine was a newer version, so it only worked on vehicles back to 1998, but with various extra plug-in cards, it will work on all Chrysler/Jeep vehicles back to 1983 models. One of those cards lets it do emissions-related stuff on any brand of car sold in the U.S. Starting with 1996 models. For that reason, a lot of independent repair shops bought them.

2004 was the first year the DRB3 was obsolete on a few Chrysler vehicles, and it no longer worked on all their models by 2008. Repair shops often sell their obsolete equipment so they can buy newer versions. That is why you will find these on eBay.

If you only plan on using this on a 1993 model, there are a lot of less-expensive scanners available. My first one was a "Monitor 4000". It looks very similar to the older Chrysler DRB2. I have two of those also. Both were built by the same manufacturer, and both require the use of plug-in cartridges specific to one year or one group of models. Those cartridges do not interchange between the Monitor 4000 and the DRB2. If you find a DRB2 on eBay, look for the 1994 "Supercartridge" with a yellow label. That came out in 1994 and consolidated all the years and models into that one cartridge. It works on all the systems on all the models through the 1995 model year, but only Chrysler products.

The Monitor 4000 does not do as much as the Chrysler scanner, but it works on more brands. Mine came with one cartridge for Chrysler, GM, and Ford, but unlike the DRB2 which had been replaced by the DRB3, there were updated cartridges available for the Monitor 4000 until at least the late 1990's. Mine also came with a dedicated cartridge just for Chrysler's computer-controlled transmissions. I never used it. I also found a separate cartridge for anti-lock brakes, but I never used that one either.

Watch out for the newer scanners that cost from around forty bucks to a couple of hundred dollars. I tried a few of them, and while they do provide sensor data, the display updates so painfully-slowly as to be too frustrating to use. The displays on the DRB2 and DRB3 update a minimum of a few times per second. The DRB2 has four lines of display. The DRB3 displays up to twelve things at once. Some of the cheap scanners update their displays as slowly as once every three to five seconds. That is totally unacceptable when you are trying to find a glitch caused by a sensor, when you are manipulating its operation.

Also, to be of real value, you only want a scanner that is "bi-directional". That means it can take information form the computers and show it to you, and you can talk back to those computers and command them to do things. A perfect example is diagnosing a bad fuel pump circuit. Electric fuel pumps only run for one second when you turn on the ignition switch, then again when the engine is rotating, (cranking or running). That means you would have to have a helper holding the ignition switch and cranking the engine endlessly while you are taking voltage readings in the circuit. That is not practical.

Another example is when working on a bad electric radiator fan. You would have to wait for the running engine to get hot enough for the engine computer to turn on the fan relay, then you can take voltage readings in that circuit.

Instead, the scanner will have an "Actuator Test Mode" where you can select the appropriate computer, then the system, then you can command it to cycle the relay on and off repeatedly while you work your way through the circuit. The engine does not even have to be running.

I owned some Fords years ago and learned to never want another one. I worked at a very nice family-owned Chrysler dealership through the '90s and got a lot of factory training. Later, I taught at my community college for nine years. Chrysler used our classroom as one of their three satellite training sites for all of Wisconsin, and the instructor let me sit in on her classes whenever I had the time. She was a former Cadillac mechanic, and they interact with their counterparts at GM and Ford, so we got to hear a lot of what was going on there too. GM and Chrysler do a lot of things the same way as far as how their cars operate, but GM is way at the bottom of the list when it comes to customer-unfriendly business practices. Chrysler is at the top of that list, after Hyundai and Toyota. Ford is somewhere in the middle of that list. I value that a lot because it relates to how I'm going to be treated after the sale.

Ford has a tendency to do things quite differently than other manufacturers. If you know how to work on a GM product, you'll find Chryslers a little easier. You'll have to start learning all over for many of Ford's system. For an '87 model car, the electrical system is fairly similar to all other cars of that time. I just don't have the wire colors memorized for the various circuits. If you're referring to a truck with two gas tanks, those will have a fuel pump in each tank. I've only read about some of the problems and repairs with the switching system. If you need help with one of those, post a new question specific to that vehicle so the other experts will see it and have a chance to reply first. They'll come and get me if they need help with a wiring diagram.

When you post the question, please be sure to list the engine size, transmission type, and mileage. We need to know the engine size to find the right wiring diagram and parts list. We look at the mileage when making judgements as to the best suspects.