no signal from ecm to fuel pump relay on 89 4.0

I bought it non-running and don't know any history on it. If I run a hotwire to the pump it runs good.

There is power coming from the fusible link to the relay and there is power to the relay when the ignition is on. Any ideas? Maybe the ecm is defective? Maybe the wire is broken somewhere between the ecm and the relay? What sends the ecm the signal to start the fuel pump? Maybe the CPS is defective.. could that cause it?

Thanks in advance for any ideas!

The '89 4.0 will have a ballast resistor for the fuel pump, located on the left fender, above the air box.

http://www.lunghd.com/Tech_Articles/Eng ... lenoid.jpg

This can be bipassed to check if it is operation properly by disconnecting both orange wires, and using a paper clip to connect them, if the engine starts and runs, that's it. The resistor is to provide full power to the pump at start up, and to "curve" the voltage durn running.

If this is still not the fix, pull off the left (driver) side tail light, and check the ground wire on the body, this ground shares with the tail lights and the fuel pump.

There is no pwer even coming from the relay because there is no ground signal coming from the ECM. There is power from the red wire that comes from the fusible link and power with the ignition switched on to the relay.

Speaking of the ballast resistor, what ohm resistor do I need to get?

I'm not sure what the ohm's would be but the last ballast resistor I replaced was with a GP Sorensen # GCR7

The relay would only have power with the ignition switch to the ON position.

And you tested the fusible link, and that's good??

I don't follow you on the "No ground signal' coming for the ECM. where are you testing this, and to what?? The red wire??

The ECM supplies a ground to turn the fuel pump on instead of supplying 12v+. When you turn on the ignition switch that automatically energizes the relay switch but it isn't grounded for the relay to function... the ecm provides this ground and none is coming from the ecm.

What I might end up doing is straight wirng a ground to the relay, that way when I turn the ignition switch on the fuel pump automatically comes on. The only problem with this is..

1. The fuel pump is always running with the ignition switched on

2. I have an accident on the road or trail and the fuel pump ruptures, the pump will spray gas everywhere until the switch is turned off. This may already be the case even running it through the ecm.

The ECM supplies a ground to turn the fuel pump on instead of supplying 12v+. When you turn on the ignition switch that automatically energizes the relay switch but it isn't grounded for the relay to function... the ecm provides this ground and none is coming from the ecm.

 

What I might end up doing is straight wirng a ground to the relay, that way when I turn the ignition switch on the fuel pump automatically comes on. The only problem with this is..

 

1. The fuel pump is always running with the ignition switched on

2. I have an accident on the road or trail and the fuel pump ruptures, the pump will spray gas everywhere until the switch is turned off. This may already be the case even running it through the ecm.

No, the Auto Shutdown Relay (ASD) will shut the pump off. I had one go bad on my 91 MJ and caused similar problems. When starting the engine the ASD relay latches and looks for the distributor to spin. If not, the ASD relay trips and cuts power to the + coil and the fuel pump. A safety thing. I would not run a seperate ground to the FP relay, if that's what you plan on doing. You can test the ASD relay by running +12V from the battery directly to the coil pos terminal. This will also backfeed 12V to the fuel pump through the ASD circuit. If the pump runs, the ASD relay is bad. If not, the pump itself, fuel pump relay, or the wiring is fubar. Worth a shot.

This thread in the NAXJA OEM TEch Discussion forum may help:

No power to ballast resistor or fuel pump

OK.....now I got ya :D

Yes, I know what you mean, and there should be a Inertia switch, which could be added. I've yet to find the inertia switch on these MJ's.

So with you straight wiring the ground to the relay, the addition of the inertia switch might not be a bad idea.

Yes, I seen Hornbord reply, and I think that where you have a problem, with the auto shut down.

So does mine have an inertia switch? I looked behind the drivers side kick panel and didnt find one there, there was the horn relay and another relay there.

Where is the ASD relay located? My truck does run if I bypass the relay so I know my coil is getting power if that matters.

The link you posted doesnt work either :D

Thanks for the help guys, if I keep hounding ya I think ya'll can tell me how to fix this :cheers:

The NAXJA link is:

http://www.naxja.org/forum/showthread.p ... 744&page=1

The ASD relay, as well as the FP relay, and the ballast resistor relay, are located in the Power Distribution Center (PDC) on my 91. You have an 89? In that case, I'm not sure if the 89 has a PDC, but the relays are there somewhere. Someone Renix guru should chime in on this. And the XLs/MJs never had an inertia switch AFAIK.

Here, try this, half way down the page, under EGR Solenold -

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

And like I said, I have not found a inertia switch on the MJ.

I'm thinking what hornbord wrote about the ASD is doing the same as an inertia switch.

And like I said, I have not found a inertia switch on the MJ.

 

I'm thinking what hornbord wrote about the ASD is doing the same as an inertia switch.

I'm not sure mine has an ASD. Where would it be?

Hey Bob, I know the HO's electrons pretty well, but am an ignoramus maximus on the Renix systems. :nuts: But I know both systems had an ASD relay; a Federal mandate thingy. In fact I remember reading about various recalls throughout the years on these relays/circuits.

Well, there are 4 relays in the same place I found the fuel pump relay. I know the second one from the front is the fuel pump but not the other three.

Let me check and see if i can get a real good diagram to show you. I will post it or email it to you.

Cole

Ok, another diagram may shed some light on this.

Hornbord - Yea, I don't know the HO at all, and still learning the Renix system myself :D

OK.....try this -

http://www.lunghd.com/On_Site_Tech.htm

Under "Engine, fuel system" > Fuel System - PDF File > Rexis fuel service manual.

But get ready for 100 pages to open :eek:

That's the complete service manual for the renix fuel system

Have fun reading :popcorn:

And you'll be an expert on the fuel system after you read the complete service manual.

I saved it for later. thanks that site looks like it has a lot of info :cheers:

Fortunately I have the day off to work on this :D

Looking at the Renix Manual, my relay may be wired wrong. I don't see how that is possible, it doesnt look to ever have been tampered with. Nothing under the hood does. Where the wires come into the block that the relay plugs into, is sort of dirty and the dielectric grease or whatever it is, is there. According to the diagram in my Chiltons manual and now this Renix manual, it is not wired right. I thought that at the time I was looking at it and wondered how it could work. There may be a signal coming from the ECM after all and I did not detect it with the test light, I never even put a meter on it. I really think SOMEHOW it is not wired right, maybe it was driven after it stopped working and thats how the relay got dirty again after it was tampered with and it looks like it's unaltered. When I got the truck it did have a hot wire running back to the fuel pump but it was disconnected and they said they didnt know what was wrong with it. I'm suspecting the fiddled with the relay then found out it was the pump or something and then the relay was screwed up and they didnt know it so they bypassed it.... but who knows.

Somebody talk me through testing the ECM feed to the relay, and what color wire to check, I am fairly sure it's the orange/black wire... right? I have a multimeter.

After closer evaluation, it's not wired up wrong. I am just going to straight wire the relay ground and call it a day. I can't think of any driveability issues by doing this.

The fusible link going to the fuel pump burned up for some reason. I decided to rewire the fuel pump relay to a factory style toggle switch and be done with it. Race cars do it, why can't i? :D Nobody will ever get far if they try to steal my truck either. like they would want that pile of #%$ to start with :oops:

The way I look at it, problem solved. Can I get a public opinion on my decision to wire the pump to a switch?

The fusible link going to the fuel pump burned up for some reason. I decided to rewire the fuel pump relay to a factory style toggle switch and be done with it. Race cars do it, why can't i? :D Nobody will ever get far if they try to steal my truck either. like they would want that pile of #%$ to start with :oops:

 

The way I look at it, problem solved. Can I get a public opinion on my decision to wire the pump to a switch?

I guess I'm weird, I like things to work as designed. What you did sounds like a bandaid, but I'm glad you got 'er going. Just remember to flip the toggle OFF if you start going end over end :brows: Did you ever find out if your rig had an ASD relay and/or an inertia switch?

It's not nearly a DD, I was just tired of messing with it because I didnt buy it to mess with a fuel pump relay :D if anybody can think of any adverse effects of doing this let me know. Does the ECM supply a stable supply of current to the pump the whole time the engine is running? I think it does, if so wiring it to a switch can't hurt anything.

If it has ASD or an inertia switch the Renix manual doesn't list them in the table of contents and it includes a component list of everything. I'll look around at Jegs and see what they have for auto shutdown of pumps on drag cars. A lot of stock cars run electric pumps also, maybe they use something to auto shutdown.

I'm wiring my a/c compressor to a switch and using it for OBA, I guess I'm just weird and don't use stuff as it is designed :D

Well mate, your fusible link was smoked for a reason. If you don't give a rat's a$$ about hot wiring your fuel pump and the possible consequences, why should I? And using your A/C compressor for OBA is an entirely different catagory. :nuts:

I am off to a good start here I see :oops:

Don't take it the wrong way. Hornbrod is just thinking about your safety. :thumbsup: