1) Put 12V and a ground wire to the fuel pump wire that would connect to the body underneath the trunk. Pump came on.

2) B]2) Put 12V to ALDL's terminal G, pump won't kick over.[/B] .

3) Underneath the driverside back seat, managed to pull out the wires, multimeter to the gray wire, zero.


Where could the wiring go bad ? Where is it connected from the engine compartment to inside the car ? I really don't feel like pulling the entire carpet *sigh*.


I guess I could hotwire the pump, 12V straight to it plus a separate ground and have it running that way, but I prefer to do it the right way.

 

When you turn the key to the "on" position, do you hear the fuel pump relay click?

I believe that the "G" terminal still has to go through the relay.

The tan wire (fuel pump power wire) won't be hot except for the 2 second prime sequence and then again once there is a distributor reference pulse OR the oil pressure switch closes - ~4 psi oil pressure is detected.

 

Yes relay clicks. I even tried swapping them out, fan and pump, since both are identical.


Oh so the gray wire underneath the carpet will only show 12 V for 2 seconds ? Even if I connect 12 V to terminal G ?


However I still don't hear the pump at all. WHERE is the bulkhead connector that runs from the engine bay to the ALDL terminal G ?


*shaking my head* I've been working for soon to be a week on this problem, tried ignition module, fuel pump etc.

 

Have you checked all wiring at the relay? The wire is still attached to the "G" terminal?

The "G" wire probably runs through the primary bulkhead which is just to the right of the brake booster (engine bay side).

 

Is that the red wire ? Just to the right of the brake booster, ok will check it out. Getting real tired of taking the bus here (car is stranded here on base)

 

The wire from the ALDL to the fuel pump relay, I THINK, is red, yes.

 

Damn hrrrmmmm

ok let me check a few things

 

Could it hrrrmmm be the ECM ?

 

OK, hooked up 12V straight to the tan or gray wire coming out from the fuel pump relay, the pump kicked in.

Bad relay ? Bad ECM ??

Looks like power may not be coming up to the relay.

 

I know it sounds weird - but try the Oil Pressure Sending Unit. The fuel pump gets direct juice from the battery to the fuel pump via the OPSU, regardless of anything else including relays, key on/off. A bad OPSU can affect the fuel pump in many ways. The OPSU is either 1) on top of the china wall, behind the intake, under dizzy, or 2) just above the oil filter. A new one is $28 at Autozone.

On my 1992, the OPSU went bad and the pump ran - always! But, I couldn't hear it, and spent weeks trying to figure out why my battery went dead every 3 days - turns out I was circulating fuel all day, all night, key in or not!

 

hmmm that is weird


OK could it be a relay though , after all ???


I was under the impression that if you go power to terminal G on the ALDL that would BYPASS the relay. However plugging into terminal G gave me no result what so ever.


Right now I managed to get it home, running it hotwired, car's loud due to us cutting the muffler off, so gotta get like a glasspack something too.

 

I did some digging around and found something that might be of use to you (the upper half):

 

Thanks man, yeah I got the entire factory manual for the 91 cars, however I don't remember anything but ... the fact that terminal G should be able to selftest if one disconnects the relay and plugs in 12V.


I may have to read it all again. Tomorrow I'll run out to the junkyard, get several relays and also connectors (I have a feeling it may be where the gray wire is plugging in to ??)

 

No, Stek is right. The 'G' terminal in the ALDL is routed to the pump through the NC contacts of the FP relay. If the relay, socket, or wiring are FUBAR, pumpie no workie.

 

check your wiring between fuel pump relay connector and ecm. the green/white wire is the one that supplies the 2-second cycle when you turn the key on, so that will only show power for that time. the gray one is the fuel pump control input to the ecm and also goes to the oil press switch, and to the pump itself. the orange wire at the connector is the power, the grn/wht wire and gray wire just complete the circuit in the relay - that circuit sounds like it's not getting completed. sounds like what you've already heard, but check those wires. as the diagram shows, they only go those components, and all easy to check. have you checked the orange power wire at all? there is an in-line fuse on that wire that goes to (1) the fuel pump, and (2) the ecm. with the relay connector off, you should show battery voltage on that terminal...

 

bingo.
thats what i was going to say..

 

The inline fuse is one of the first things I checked, it's good to go.

However I went to the junkyard today and grabbed a couple of relays together with their connectors.


I was looking at how the fan relay and fuel pump relay is, yes they're identical, but it looks like the wires are not hooked up identically, so the relay may work bad for the fuel pump who knows, I think it's the connector itself. Looks like circuit 120 remains open.

 

the relays are the same, but the connectors for fan(s) and pump are NOT wired the same.

if you have everything put together, relay installed, etc., and turn the key on, do you get the fuel pump cycle for 2 seconds, or not? if you don't, take the relay off again, and hook a test light or volt meter to the terminal that has the green/white wire. turn the key on. do you get a light or voltage? if you don't, you need to check those wires from the i mentioned earlier. if they are good, there is a switch in the ecm that cycles the fuel pump and has probably gone bad. it cycles the pump when the key is turned on, and not again until the distributor tells it that there is rotation. the gray wire going to the ecm pretty much only tells it that there is sufficient juice to the pump to run it, that same wire goes to your pump to power it. the oil pressure switch is really not an issue here, if you're not getting the 2-second prime on the pump. other connectors and relays aren't going to fix it unless all of your relays that you've swapped are bad, but that's not very likely in my opinion.

 

Hmmmm the green/white wire goes in to the ECM huh ? Well that's the one I had spliced in to by mistake before. I'll swap out the connector and relay tomorrow, if that won't fix it, possibly a bad ECM ?


Right now what I'm doing is this, hot wire from battery spliced into the gray wire from the fuel pump relay, when I park the car I disconnect it.

Would the possible fault in the ECM drain the battery though ?

 

no, shouldn't drain the batt... something else i thought of, was the ECM fuse in the fuseblock itself - if you weren't getting the 2-second cycle. but since you say the car runs with a hot-wired fuel pump, then that wouldn't be the problem, cuz you'd know it. but what i was gonna say was that if you got no initial cycle, to check that fuse, too, cuz if it was blown, you'll never get that cycle. the fuse under the hood supplies a constant voltage to the ecm for memory, like on the radio. the fuse in the fuseblock turns the ecm on when you hit the key. i just went thru hell with my fuel pump, so i know the circuit pretty damn good and how it works... if you want to call me for some 1-0-1 help, lemme know, i'll PM my number to you. i'm east coast, but that's ok cuz i'm not working this week.

 

Thanks, if I can't fix it I will. I did check all the fuses though, but like I said, going to swap out the relay AND the connector to it today and see.

 

Yup, got much worse.


I used an old connector from the junkyard, something happened. Couldn't start the car. Even by hooking up a hot wire to the fuel pump relay's gray wire. After a while it seemed like I could start it by holding down the throttle a little bit. (With the gray wire hotwired that is)

I checked the inline fuse, blown just after the last work, so I replaced it.

Still the same result, so I checked the fuse again and it was still good.


I ran the codes, and of course no code 54 BECAUSE the hotwire to the gray wire closes circuit 120. However this time I got another code instead, Code 42.

Unfortunately I left my factory manual at work, but checked in the Haynes manual:



Code 42 - Electronic Spark Timing

Poor electrical connection, open or short in circuit, defective ignition module, defective ECM.




I only have tomorrow to work on it, since I'm flying out to NJ for a few days after that, will be back late late Sunday night. Kragen's useless, I'll have to take the ignition module to Napa or Autozone, much farther away for me by bus, however how can one check the ECM ?

Now remember, if I would disconnect the hotwire I would probably get a Code 54 as well, so the original problem still remains. But now since the Check Engine Light stays on when I'm driving, I didn't dare to go more than just around the block to park the car.

 

Code 42 has nothing to do with the ignition module or the ECM - it has to do with the EST - Electronic Spark Timing - the wire that controls computer controlled timing advance - in other words, your EST wire is disconnected - it's under hood on the pass fender, close to the shock tower, tan/black single wire with a connector in the middle - reconnect it, and go from there. Search EST or timing wire here and I'm sure you'll find a pic of it and it's location. The EST being disconnected will cause the SES light to stay on, and cause the car to run badly since the ECM can't advance/retard timing.

Find this EST wire, make sure it is connected and no shorts in it. Then try the car, see if the SES light goes out.

If you still have fuel issues after that, try the $28 Oil Pressure Sending Unit I mentioned earlier - it's just above the oil filter - replace it. Regardless of any Haynes wiring diagram (which by the way neither Haynes nor Chiltons has the electric wiring diagram for a TBI car, only TPI and carbed) - I promise you that there is a direct connection between the battery and the pump via the OPSU, and nothing else, not even a hot-in-run - just a straight positive from the battery to the OPSU to the FP.

 

during all this time, did you ever get the initial 2 second prime cycle when you turned the key on? i don't think you ever said you did or didn't. the ecm powers the fuel pump if it's getting a reference from the distributor and voltage signal from the pump, basically. yea, if you disconnect that gray wire from the source of power, you're gonna get a code 54. the code 42 doesn't have anything to do with the pump, only for timing. is that wire disconnected? also, as far as the ignition module goes, the initial 2-second prime will still do just that - it's independent of the module. however, it will not power up the pump (through the relay) without the module being in place (distributor reference). ecm is primary source for fuel pump, oil press is secondary if the ecm fails. have you checked those wires at all? i don't know of any way to check the ecm. the only thing you can do is check your wiring and module and if all that's good, then it's probably the ecm. remember there is a switch in there. but if you're not getting a 2-second prime signal at the relay, you need to find out why. you don't have to hear the pump - you need to check for that signal. you said in an earlier post that you had spliced in to that grn/wht wire? for what, and did you put it back to its original configuration? it's an overall simple system and circuit, but if your wires are bad, you're wasting time with connectors and relays. i wouldn't worry about the pump itself just yet, but you need to check all the wires on that relay connector to ecm and oil press switch, and to the connector on the firewall in the back of the car, and the wires to the ecm from the ignition module. whatever changes you made, like a different connector, you need to verify, or put the original back and still verify the wires.

 

Yeah I may have to go and get a new connector for the relay, since I replaced it with a used connector, and cut the wires too short on the original one

No, I never ever got the initial 2 second prime.


Reason I'm running a hotwire to the gray wire is because I was tracing the problem from the tank, trunk connector, wires underneath the back seat.


Too late for the pump though heh .. since I replaced it a few days ago.

 

well a used connector is still ok, but you have to make sure you made good connections on your splices...

never a 2-second prime, huh? if you never got that, your pump will never run via the ecm. not sure if it'll even start via the oil press switch. bypass (hotwire) is about the only other way, as you've already done. you definitely need to check the grn/wht wire to the ecm...

 

AND .. that is the wire I had spliced in to .. originally. All by misstake since I confused the two relays, yup was splicing into the green/white wire for a manual fan switch.


EST connector is hooked up, I even disconnected it and hooked it up again.

 

I know this is a 2 year old post, but I am having fuel pump gremlins myself.

I have a 1988 TA just swapped from a 5.0L TBI to 383 TPI.

I had trouble getting pump to run. I checked for voltage at fuse on fender, no voltage to ground, fuse was good. After studying a Mitchell diagram from another post: I can see that the ECM supplies batt power to relay via grn/wht wire to power pump via relay.

I am assuming that the ECM uses the tan/wht wire as it's reference for turning on or deciding to turn on relay via the grn/wht wire.

According to the illustration, it would appear that the fuel pump will run if oil pressure switch is closed. Seems bizaare they would wire it this way, since a bad oil pressure switch would cause pump to run without ign being on.

Anyway just dropping engine in for first time, we wanted to hear it fire. I had not volts at fender fuse, so I jumpered batt+ to relay connector until I heard pump run (I think I jumpered to tan/wht). Pump ran and pressure went to 43 lbs. I cranked and engine fired, but suddenly as pressure dropped down to like 32 and lower, relay clicked madly (as did pump) and it stalled out.

I beleieve we may have run the pump dry since tankw as low, and pump eventually stopped running altogether.

I installed a new inline MSD pump with it's own ground, and own positive (for the moment). It's pulling through dead OEM replacement in tank pump at the moment.

Currently, since I was away from car for a day; something died, and I get no check engine light, (ECM fuse is good).

I just wish I knew what that inital clicking was. It only happened under cranking. I don't understand what would cause it, (the pump? an ign wire firing to a computer ground? I have 8.8 wires)

So, I guess after I check leads to ECM for power, a new ECM may be in order.

It would seem that is there was no power to that fender fuse, that explains why pump didn't run on it's own at first attempt. There was a harness swap, and I did double check fusible links at starter. AGH!!

Yes, grounds are all connected at head and firewall.

I guess what I fail to understand is the role of the ECM in controlling the pump during run (if at all). I assume that ECM powers pump (2 secs), then the tan/wht (oilpressure switch) powers fuel pump relay the rest of the time?