93 Dakota, no start. UPDATE and answers

The morning started off pretty bad. I went out to start my 93 Dakota 4x4 with a 3.9 Magnum and all it would do was crank over. It ran Monday, and has about 1/2 tank of gas.

I don't hear the fuel pump, so I pushed the plunger in on the fuel line Schroeder valve and got a little dab of gas at a little pressure. (I do not have a fuel pressure gauge), so I checked for spark (by myself here) and I don't see any spark. I tried cranking again, but no start. So I checked the Schroeder valve and no fuel this time. I do not have voltage at the coil.

I have battery voltage to the fuel pump relay with the key in the on position. I swapped a few relays around, and try to start again. Crank only. Check the Schroeder valve again, no fuel.

1) I thought I should be able to use a jumper wire across the fuel pump relay and run the fuel pump, correct? No pump, no fuel at the valve.

2) I'm concluding I have no spark because I have no fuel pressure, correct?

3) Am I correct in assuming I have a dead fuel pump, have 158K on what I believe is the original pump.

4) I have here (2) 1991 Dakotas that were throttle body injected (La 3.9). Will the fuel pumps from the 91 throttle body trucks work with my 93 port injection truck? Gene

Shooting from the hip.......no the tbi pump will not put out enough pressure for the port injection.

Best bet there is to check part numbers on Rock auto.

Used to do fuel pump tooling for GM, tbi pumps were totally different from port injection ones.

Ed

Smack the gas tank a couple of times near the fuel pump. Sometimes it will jar the pump enough to get it working again. If it does then get a new pump.

I'll try to answer here the best i can for ya since you have multiple questions in one here. First I would check and make good and sure you don't have spark. I bet you probably do but if not that is a different issue than no fuel pressure unless there is a security problem or engine controller problem then it might affect both.
1) Yes, you should be able to jump the relay and power the pump all the time outside of the 2 second initial run time.
2) Fuel pressure will have no effect on ignition spark. (Unless its a anti-theft issue then thats a whole other deal)
3) I'm betting your pump is probably dead. Stumpy is right try cranking it while someone smacks the tank you might get it to run but replacement is needed very soon to fix it.
4) I don't think the pumps are the same. I defiantly know the pressure is different but I can't remember where it is regulated.
Hope this helps a little.

how did you check for power at coil, key on will NOT provide voltage unless the ASD relay is energized.
If you truly lost fuel pump and spark, most likely the corroded /broken wire in the harness on the driver side.lost power to fuel pump relay and ASD relay. fixed dozens for this problems.
does the check engine light come on with the key turned ON? If NO, I would bet on a broken wire.
a love tap on the gas tank can sometimes jump start a bad pump,won't help at all if you have a wiring issue.
TBI pumps operates around 10-15 psi. the port fuel around 40 psi

I had the exact same cranking-like-crazy but no spark, no fuel pump, no nuttin' in my '96 Dak 3.9 about 4 years ago.

Loooonnnggg story short, I did all the troubleshooting I could think of, including checking for the infamous corrosion in the wiring harness deal (it was perfect - living in SoCal has it's advantages).

After trying everything I could think of and posting my problem on this board, (got lots of good advice) I ended up replacing the PCM and it fired instantly. Been running perfect ever since.

the most common thing to happen is the fuel pump----before you just hammer on the tank get under there and look for an indent about the size of a coffee can lid----that is where the filter and pump assembly is at----get a rubber hammer and really hit it----have someone doing the starter at the same time-----there wont be enough room for a baseball swing so dont worry about hurting it-----on the computer problem----one of my friends owns a junkyard---every time some one buys the computer he asks them if they are really sure---he says about 90% of the time they come back and buy some other electronic ---most admit the computer didnt fix it.....

I don't believe its the wiring (I did untape the harness between the battery and past the part that goes inside and looked, all the multiple wire connections look good and passed the tug test. Years ago I discovered the broken wire deal, checking for the broken wire was one of the first things I did.) I have battery power to the all the relays with the key on. I have no check engine light, but I don't ever remember having one in the 5 years I've driven this truck.

Its kind of hard to check for a spark when your by yourself. I turned the key to on, put a screwdriver into the coil wire end (female end) and held it close to the AC compressor (thinking it should be a good ground) and jumped across the starter relay to crank the motor. I didn't see a spark, but I was doing a lot of stuff at the same time. I also didn't think there would be a spark if the ASD relay didn't get the signal there was fuel pressure. I did check for power with the key on at the plug to the coil and tested it with a test light and did not see a light, but as I think about it, isn't that suppose to have 5 volts? My test light won't light with 5 volts. I guess I will have to locate a wiring diagram specifically for a 93 Dakota and do more digging.

According to online listings for fuel pumps, they fit all Dakotas with 2.5, 3.9 and 5.2 from 91 through 97, only one listing for a fuel pump per brand/ price range (several brands with only 1 part number). I can buy one online for around $60 and up, at all my local auto parts stores the pumps start at $160 and go up! Maybe tomorrow I'll smack the tank and see if it will start, but I won't be able to be cranking it while I smack it. My arme are not that long...Gene

The coil is 12 volts.Turn key on, relays will energize for about 2 seconds then go off.Then energize again during cranking.You will only have voltage to the coil for those 2 seconds that the relay is on. even if no fuel pressure, spark should be present. pull the fuel pump and asd relays and check for powers. you should 2 voltage sources. 1 with key on only and another constant power(battery power) Spray some carb cleaner or staring fluid down the throttle body, see if it sputters. help confirm spark or no spark,Narrow it down to just a fuel pump issue. even possible for a bad PCM. check the main harness ground at engine. not the battery ground. eyelet lets loose on occasion also.usually on the front engine bracket.

I'm fighting a similar prob on my '91 TBI kota. Won't start when warmed up.
Tried coil and PCM. Def ignition because starting fluid doesn't do a thing.
Fuel pump was replaced several years ago. I'll recheck the wiring and try the pickup coil next. Runs perfect when cold, but will eventually die if left running after warmed up, until whatever is failing cools completely off.
Very annoying, to say the least.
Just to add, the coil gets "normal warm", not too hot to touch.

UPDATE: The problem was a broken wire. I did not unwrap my harness far enough back. The broken wire was a 3 red wires with orange tracers on one side of a butt connector, and one red wire with an orange tracer wire on the other side. That junction was located in the main harness directly under the under hood fuse box. The wires were the battery hot to the relays.
Apparently, when I tested with the test light there must have been a few strands still making connection. When I tested this morning with an ohm meter, I had 600 ohms on the ASD and the fuel pump relays, and 0 ohms on the start and AC clutch relays. By the time I got the tape off the harness, one wire had completely broken away. This location had already been repaired before. I want to note that there was no visible corrosion at the butt connection, the wire was simply broken. This time I spliced in an additional wire to the 3 existing wires, installed a wire nut and sealed it with liquid electrical sealer. The added wire was about 6" long, and I spliced the other end with the other red/orange tracer wire with a wire nut and also sealed it with the liquid sealer. Then I re-taped the harness. The truck purrs like a kitten.


Kowalski-440 You might want to look for that red w/orange tracer wire connection. If there is a lot of corrosion at that splice it could create a lot of heat the longer is got power going through it, and heat will build up resistance, maybe enough resistance the needed amount of current can get through.

Anyway thanks for the help guys, the truck runs great after fixing the broken wire. Gene

This is right. I fixed many wire harness on the Dakota's also in my years at the Dodge dealer. And as was said you should have two power wires at the ASD relay with the key on as one is ign switch volts and the other is hot all the time. Also I believe it was in 1992 that Mopar started using a seperate fuel pump relay along with the ASD relay. The pump relay supplied the fuel pump and the ASD supplies the coil and injectors but the two relays share the same ground terminal on the PCM so they work together. Also if you can get a scann tool check and see if its seeing the cam and crank sensor signals as it needs to see them in order for the PCM to ground and turn on the ASD and fuel pump relays. Good luck , Ron

I'm glad you found your problem but, wire nuts? Seriously? Those are for houses that don't drive crappy roads or otherwise move every time they are operated. Solder those wires and use heat shrink with sealer in it before you burn it to the ground.

Hall effect pickup it sounds like. I just went through that on my '91 a couple months ago.

If you saw me solder wires, you would think the wire nuts were an improvement. I believe the wire nuts will be OK. They are tight, and are sealed with liquid wire tape (good for 600 volts) and then wrapped with electrical tape with the wires and wire nuts folded back and taped together on both ends, then the whole loom is taped tight the full length. The worst that can happen is I will loose the connection, the wires can not touch ground. The next option is to use crimp on butt connectors with tape (which was more then the last fix was, over 5 years ago, before I got the truck).

The next residence for this Dakota is the scrap yard. It has nearly 160K miles (everything is still original, and its a 4x4) and the entire bottom is crusty, nothing bolted under the truck will come apart without breaking the bolts. Its one under the truck repair from being scrap. When I thought the fuel pump was bad, I would have cut an access hole in the floor of the box to change it, then patch up the hole.
I am currently collecting parts for its replacement now, I don't drive the truck much in the summer, probably less then 1,000 miles. I'm hoping the replacement will be ready before I need this truck next winter. Gene