need all fuse locations for '87

[nada1]

I am without the common owner's manual for an '87 I am working on. I need to know where all the fuses are for the fuel pump. fuse panel at rt of dash does not identify them (?!) it works when 12v is applied to terminal G of ALDL, not when engine is starting. engine runs until fuel is gone, shuts off.

thank you

 

[boomdriver]

I am without the common owner's manual for an '87 I am working on. I need to know where all the fuses are for the fuel pump. fuse panel at rt of dash does not identify them (?!) it works when 12v is applied to terminal G of ALDL, not when engine is starting. engine runs until fuel is gone, shuts off.

thank you

back to the fuasble links and oil pressure switch.

 

[nada1]

back to the fuasble links and oil pressure switch.

engine shows plenty of oil pressure, even cranking. some c4s have a secondary FP2 fuse, not sure about the 87, not even sure of the fuse location for FP1 in the panel, without the manual. mine is #24 on the 91.
the owner is checking fusable links, visually for time being. from where these are in the loop, I'd guess that fusables are first, or closest to battery source, rather than fuse or relay, is that accurate?

thanks

 

[boomdriver]

engine shows plenty of oil pressure, even cranking. some c4s have a secondary FP2 fuse, not sure about the 87, not even sure of the fuse location for FP1 in the panel, without the manual. mine is #24 on the 91.
the owner is checking fusable links, visually for time being. from where these are in the loop, I'd guess that fusables are first, or closest to battery source, rather than fuse or relay, is that accurate?

thanks

The links are under the battery...

the FP gets alternate power from a switch in the oil pressure circuit. the FP relay is unimportant. If there is no power to the relay, its pretty cut n dried from there..
The power source TO the pressure switch IS important.

The fuse for the FP Is marked in the fuse panel. It may be FPR, or FP, or some variation of F...something, but its there.

 

[nada1]

The links are under the battery...

the FP gets alternate power from a switch in the oil pressure circuit. the FP relay is unimportant. If there is no power to the relay, its pretty cut n dried from there..
The power source TO the pressure switch IS important.

The fuse for the FP Is marked in the fuse panel. It may be FPR, or FP, or some variation of F...something, but its there.

still learning a morsel at a time...

question 1: I gather that the oil pressure sending unit is the same as that dispayed on the dash panel, or no?

If the ecm needs the 4 lbs pressure signal, with the piulses from the distributor, to start the injectors and to connect the FP relay, then the engine should not start, even if the fuel rails were pressurized by jumpering terminal G on aldl. no injector pulses. is the logic correct or am I off track?

the vehicle owner verifed that the lower rt fuse -unlabled- had no current signal for 2 secs when key was turned on. I was sure that had nothing to do with low pressure oil signal -since there IS no oil pressure at that point. in 2 days he never once heard the FP when key was turned on., thus i was looking for the fuse(s) location.
then, by sheer luck, he was searching over the fusible links, and "thought" the oil sending unit plug was not seated. he reseated it and the FP now works.

happy ending, except that it does not follow logically. if the missing signal prevented the engine from starting, after numerous attempts, but then the engine started when fuel rails were filled, and ran until that fuel was used up, why was he unable to get the FP in the circuit when key was turned on? and, how was the ecm able to energise the injectors?
if I am not confused then it should hold that the oil sensor unhooked will prevent an engine from starting and running, even for a few seconds, which was not the case.

my guess is that he changed something in the wiring mess while working on it.

any comments would be appreciated. thanks

 

[boomdriver]

still learning a morsel at a time...

question 1: I gather that the oil pressure sending unit is the same as that dispayed on the dash panel, or no?

If the ecm needs the 4 lbs pressure signal, with the piulses from the distributor, to start the injectors and to connect the FP relay, then the engine should not start, even if the fuel rails were pressurized by jumpering terminal G on aldl. no injector pulses. is the logic correct or am I off track?

the vehicle owner verifed that the lower rt fuse -unlabled- had no current signal for 2 secs when key was turned on. I was sure that had nothing to do with low pressure oil signal -since there IS no oil pressure at that point. in 2 days he never once heard the FP when key was turned on., thus i was looking for the fuse(s) location.
then, by sheer luck, he was searching over the fusible links, and "thought" the oil sending unit plug was not seated. he reseated it and the FP now works.

happy ending, except that it does not follow logically. if the missing signal prevented the engine from starting, after numerous attempts, but then the engine started when fuel rails were filled, and ran until that fuel was used up, why was he unable to get the FP in the circuit when key was turned on? and, how was the ecm able to energise the injectors?
if I am not confused then it should hold that the oil sensor unhooked will prevent an engine from starting and running, even for a few seconds, which was not the case.

my guess is that he changed something in the wiring mess while working on it.

any comments would be appreciated. thanks

Ok, 1st,
forget the low oil press switch....Thats a back-up system, separate source of power to the pump.

Power to the relay from/thru links & fuses works in conjunction with the ECM to generate the proper signals to the right things at the right time...
Key ON, ECM supplys power to the relay for 2 sec to "prime" fuel system. No more power to the pump until A...there is a reference signal from the distrib, OR there is some increase in oil pressure which closes a switch in a separate circuit that can then send power directly to the fuel pump. Once the engine is running, the 'run' signal and OK from the ECM is in place as there are constant dist pulses, and the constant oil pressure keeps that switch closed so there is al2ways a complete path for power to the pump.

Ok, key On yeilded no 2 sec prime. Sowhat? As the eng cranks for 3-4 seconds it builds just enough oil pressure (unless its weak) to close the switch and cause operation in back-up mode for the FP. The owner may not have been cranking it long enough to build a fire, and/or the plug to the switch was off as I suggested in the other forum or a previous post, so it failed to fire because the direct routes were cut off.
The last route is the ALCL ground which enables every thing by going around the ground path control.
That may be where the confusion is....

Everything here is managed by ground path completion while most things have power ON at all times. Its the ground thats important and which path is used. When grounding the diag link, it grounds it all so everything comes alive. There is/was power somewhere in the FP relay either thru one or the other 'hots' or the control or reference wire. The ground is always there, just not complete in the ECM.

You really need a FSM electrical book to see what I'm not describing very well....

It runs now, the plug on the low pressure switch is most likely why it did'nt, and it may still have a bad FP relay.

BTW...the low press switch is only a off/on switch 2 wires. The press sending unit is (1 wire) the bulb just below the switch thats mounted on the "T" behind the left side cyl head. That particular section of the harness is extremely fragile with the most important grounds spliced in at the same place where all the inj controls/sensors and left bank FI plugs are all spliced in. Basically, the more you mess with it the more those splices come apart. That 1 wire on the sender is what the digital gauge uses. Temp senders. sensors and displays are a whole 'nother story. There are 4 temp sender/switches screwed in the block/heads or intake. None share info.

 

[nada1]

very good info

thanks, boomdriver. much of it is "digestible." I believe his issue was that he has been causing and correcting the problem by tugging, exploring, cleaning, dressing wires, under the hood. meaning it is still not fixed. the 87 has the plug on the sensor accessible, wheras my 91 requires a twenty minute ordeal to get to it.

from your comments, if the key is on, relay out, there should be no 2 sec prime, which is what he had. so the engine was maybe running on oil sensor signal bypassing relay, but was primeing rails only when cranked, not when key was on.

its only important now because truth is important.


jc

 

[boomdriver]

yeah,

I drove mine to the auto parts store with the relay in the passenger seat....

The system is designed that way so there is not a total fuel system failure over a relay. The only downside is that it takes more cranking time on cold starts to get it to light up. This is where an oil pre-tension system would aid in start up.....
where there is oil pressure, there is fuel pressure.

It used to be believed that this was an engine safety device that could shut the engine down in the event of a total loss of oil pressure. It might work that way, but its purpose was/is simply to back-up the FP relay.

From experience, there is LOTS of damage to be done by tugging on the harness running along the firewall behind the left bank...there must be 10 splices there and they are only secured by black tape inside the plastic sleeve. I had to cut out all the left inj harness and solder in new wire and plugs because it was all rotted. The car would'nt pass smog until I did that.

 

[Hib Halverson]

I don't have an easy way to post copies of the wiring diagram out of the 1987 Factory Service Manual and, even if I did, doing so might violate some copyright GM has, but I can explain how the fuel supply system is wired on an '87.

The fuel pump and the ECM get their power from one of two fusible links, in this case "fusible link H", connected directly to the battery positive post. From there current flows to Splice 106 located at the right-rear of the engine.

From S106 two orange wires go to the B+ connections on the ECM, one orange wire goes to the power supply connection on the load side of the pump relay, and one red wire goes to the oil pressure switch which is not the same as the oil pressure sender. Both are screwed into an oil manifold at the rear of the engine.

From the oil pressure sw. a red wire runs to splice 107, right near S106, and then to the fuse block and the hot side of the FP fuse, of which there is only one. S107 also supplies power the ECM's fuel pump input and the MAF.

From the fuel pump connection on the load side of the fuel pump relay, another red wire goes to S107. From there, a red wire runs to the fuse block and the FP fuse. From the load side of the FP fuse a tan/white stripe wire runs back to the pump.

One side of the control coil of the FP relay (green/white stripe wire) connects to the ECM's fuel pump control output and the other side is grounded to G104 which is the ECM ground at that big bolt above the oil filter.

When the ign. key is in "run", the ECM's fuel pump control output energizes the FP relay's control coil and that both switches on the fuel pump and energizes pin-G on the DLC. The ECM supplies power to the FP relay's control coil for either two seconds or as long as it detects ignition trigger impulses. After two seconds or once the ECM detects no trigger impulses, the ECM cuts power to the coil, the relay opens and power disconnected from the fuel pump.

Meanwhile, the oil pressure switch closes as soon as oil pressure rises to about 4psi. That provides a back-up power supply in the event the fuel pump relay fails. Since it's not closed until oil pressure rises to 4 psi, if the FP relay fails, longer than normal cranking times may result, but the engine will eventually run. If both the oil pressure switch and the FP relay are faulty, the engine will not run. Obviously, if the pump, itself, is faulty, making less than about 25 psi fuel pressure, the engine won't run.

Hope this helps. Good luck on fixing it. Happy 4 July.

 

[nada1]

I don't have an easy way to post copies of the wiring diagram out of the 1987 Factory Service Manual and, even if I did, doing so might violate some copyright GM has, but I can explain how the fuel supply system is wired on an '87.

The fuel pump and the ECM get their power from one of two fusible links, in this case "fusible link H", connected directly to the battery positive post. From there current flows to Splice 106 located at the right-rear of the engine.

From S106 two orange wires go to the B+ connections on the ECM, one orange wire goes to the power supply connection on the load side of the pump relay, and one red wire goes to the oil pressure switch which is not the same as the oil pressure sender. Both are screwed into an oil manifold at the rear of the engine.

From the oil pressure sw. a red wire runs to splice 107, right near S106, and then to the fuse block and the hot side of the FP fuse, of which there is only one. S107 also supplies power the ECM's fuel pump input and the MAF.

From the fuel pump connection on the load side of the fuel pump relay, another red wire goes to S107. From there, a red wire runs to the fuse block and the FP fuse. From the load side of the FP fuse a tan/white stripe wire runs back to the pump.

One side of the control coil of the FP relay (green/white stripe wire) connects to the ECM's fuel pump control output and the other side is grounded to G104 which is the ECM ground at that big bolt above the oil filter.

When the ign. key is in "run", the ECM's fuel pump control output energizes the FP relay's control coil and that both switches on the fuel pump and energizes pin-G on the DLC. The ECM supplies power to the FP relay's control coil for either two seconds or as long as it detects ignition trigger impulses. After two seconds or once the ECM detects no trigger impulses, the ECM cuts power to the coil, the relay opens and power disconnected from the fuel pump.

Meanwhile, the oil pressure switch closes as soon as oil pressure rises to about 4psi. That provides a back-up power supply in the event the fuel pump relay fails. Since it's not open until oil pressure rises to 4 psi, if the FP relay fails, longer than normal cranking times may result, but the engine will eventually run. If both the oil pressure switch and the FP relay are faulty, the engine will not run. Obviously, if the pump, itself, is faulty, making less than about 25 psi fuel pressure, the engine won't run.

Hope this helps. Good luck on fixing it. Happy 4 July.

Mr. Halverson, thanks for a thoughful and intelligent comment, albeit a little late..
Like Chrustmas, it's the thought that counts. Boomdriver had helped me see the flaws in my logic.

The oil pressure switch (closed at 4 psi) -to the FP relay- can be fine, but could be unplugged, of course, thus no signal. There is a huge amount of information on these cars to absorb, and one tidbit of incorrect or misunderstood info can derail the thinking process.

I will save this info for future use, and I know others will, also.

Is it the 4th already??