Hello all, (86 2.8 V6 Auto) Getting quite frustrated with the ongoing Fuel Pump Relay problems ive been enduring for over a year. Ok so here it goes:
Key On, No Pump noise
Pump works fine when you jump the two wires by the Fuel Pump Relay
Brand New Relay
Clip is clean from any residue and I get infinite ohms on Pin D (Orange and Black Wires), 0 Ohms for Pin C (Ground Wire), 0 Ohms for Pin B (Tan/White Wire) and 6 Ohms for Pin A (Dark Green and White Wire)
Power to Pin G on ALDL does nothing
Good 10 amp Fuse for fuel pump
So with D and B jumped to each other the fuel pump runs continuously and the car runs and drives fine but that means you have to continuously take the fuel pump fuse in and out. Not sure what the problem is but need help ASAP.
Have you checked the oil pressure switch? If the ECM does not see pressure it shuts off the fuel pump but it is supposed to let it run at start for a few seconds to start the car. Perhaps the pressure switch is defective.
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07:06 PM
Mike Gonzalez Member
Posts: 5093 From: Colorado Springs, CO. USA Registered: Jul 2001
The oil pressure switch is supposed to supply power to the fuel pump once oil reaches 4 psi, The ECM has no input as to oil or fuel pressure.
Since you get fuel pump if you bridge accross the relay, we know the pump and power to it are good. We assume the new relay is good. When you turn the key on the green wire to the relay should get power from the ECM for about 3 seconds. If not your ECM is not telling the relay to switch.
The oil pressure switch is supposed to supply power to the fuel pump once oil reaches 4 psi, The ECM has no input as to oil or fuel pressure.
Since you get fuel pump if you bridge accross the relay, we know the pump and power to it are good. We assume the new relay is good. When you turn the key on the green wire to the relay should get power from the ECM for about 3 seconds. If not your ECM is not telling the relay to switch.
So if the green wire does get power for 3 seconds, then what should I look for?
Get a new realy receptor and relay off of ebay, 40 amp . Get rid of the gm receptor. Mine shorted out twice. wire the new one in accordingly. I hav enot had any more problems with this .
Make sure the black wire has a good ground at the relay connector. Make sure all the tabs in the connector are clean and still making a tight connection.
Might need to bench test the relay by applying 12v and ground to the tabs the black and green wires go to and checking continuity between the other two tabs.
[This message has been edited by Mike Gonzalez (edited 02-25-2013).]
Is that 12 volts with the relay in? if not hook up the relay and check the pin from the bottom if it reads 1.something volts or anything less than 12 ecm is messed up.
------------------ 88 coupe 4 Banger 86 SE v6 needing more work yet 86 GT needing TLC
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07:09 PM
Mike Gonzalez Member
Posts: 5093 From: Colorado Springs, CO. USA Registered: Jul 2001
It sounds like all the wires are doing what they are supposed to, as is the relay. It SHOULD be working, we are missing something, Im thinking the connecot is bad somehow.
Yes usually it will read 12V with the relay out but with it in you will not have much if any voltage if the ECM output is bad.
If you ecm output is bad you have two choices. Replace the ecm or you can build a booster circuit to increase the output power. I have a circuit I have posted for others if you able to put a few parts together.
[This message has been edited by Dodgerunner (edited 02-26-2013).]
Yes usually it will read 12V with the relay out but with it in you will not have much if any voltage if the ECM output is bad.
If you ecm output is bad you have two choices. Replace the ecm or you can build a booster circuit to increase the output power. I have a circuit I have posted for others if you able to put a few parts together.
I consider trying it! Do you have a link?
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10:27 AM
Marvin McInnis Member
Posts: 11599 From: ~ Kansas City, USA Registered: Apr 2002
If the ECM does not see pressure it shuts off the fuel pump ... Perhaps the pressure switch is defective.
That is incorrect. The ECM does not "see" oil pressure or the OP sender. The fuel pump switch in the OP sensor operates in parallel with the fuel pump relay, so their operation is completely independent of each other. The OP sender may indeed be defective, but that isn't the primary problem.
[This message has been edited by Marvin McInnis (edited 02-27-2013).]
That is incorrect. The ECM does not "see" oil pressure or the OP sender. The fuel pump switch in the OP sensor operates in parallel with the fuel pump relay, so their operation is completely independent of each other. The OP sender may indeed be defective, but that isn't the primary problem.
Sorry, I don't recall the wiring details from memory, and I don't have an '86 FSM readily available, but the schematic diagram is where I would start. My initial impression is that your problem seems to be upstream of the fuel pump relay ... which would narrow the problem to either one of two wires or the relay driver in the ECM itself. You don't mention, but has the car ever been modified to install a security system or something like that? Hacked-up wiring is a common problem in cars as old as ours.
[This message has been edited by Marvin McInnis (edited 02-27-2013).]
All the reading and test you did at the beginning of this post seem to indicate that the ECM output is the problem. If you can measure the ECM voltage output with the relay connected and it's almost 0 or less than 4 volts then the ecm output is the problem. The FP output is a sourcing (provides voltage) which is a much weaker ecm output than one that sinks. (provides a ground).
If this sounds correct you can add this curcuit and it should salvage you ecm. It uses the little bit of output the ecm has and boost it so it can again drive the relay coil. Uses Radio shack part #'s.
[This message has been edited by Dodgerunner (edited 02-27-2013).]
Thanks to Dodgerunner for posting the schematic. Given what you've already done I would propose the following steps:
1) Remove the FP relay from its socket. You should see +12 volts (with respect to ground) at pin A for a second or two after the ignition is switched to "run." If not, that indicates a problem with the driver in the ECM or an open condition in circuit 465 (the green/white wire).
2) Measure the resistance of the relay coil itself (not the socket), between pins A and C. 6 ohms seems really low for this relay (it would mean 2 amps through the coil), but I don't have one handy to test myself. Since the relay should include a snubber diode (not shown in the schematic) in parallel with the coil, you may have to reverse the test leads to get an accurate resistance reading. Are you sure you have the correct relay?
3) You report that applying 12 volts to pin G of the ALDL connector does not cause the fuel pump to run, which implies another wiring problem. When you jumper pins B and D at the relay socket you should see +12 volts on ALDL pin G. Do you? Are you sure you're correctly identifying ALDL pin G? (N.B. The ALDL connector in Fieros is "upside down" when compared with its orientation in most other GM cars and in most illustrations.)
Let us know what you find.
quote
Originally posted by Dodgerunner:
Assuming a conservative current gain (beta) of 20 for each transistor, reducing the value of the 3.3K resistor to ~240 ohms (1 watt) would guarantee saturation of the PNP output transistor in the "on" state (at 1 amp Ic) and might improve circuit operation slightly. At the same time I would also add a 10K resistor between the base and emitter of the PNP transistor to guarantee cutoff in the "off" state.
[This message has been edited by Marvin McInnis (edited 03-01-2013).]
I changed out the clip and still no good. Checked the voltage on Dark Green and white wire with relay connected and 0 voltage. So like Dodgerunner said its either new ECM or his circuit. I want to attempt this circuit but I 1. Dont understand what im looking at with that picture and 2. I don't understand electronic lingo. Speaking to a laymen folks! I really would like to fix with a circuit before I have to go get an ECM! If anyone can help me out with this I would really appreciate it!
get a new relay and receptor from ebay like i said before. My headaches were gone after i got rid of the junk gm receptor. Two gm receptors gone bad. They are cheap on ebay. a small investment. No one else has had any solutions. My gm receptor was shorting to ground internally. After learning that each relay was not the problem and i could run the run with a bypass, what was left.
