hey everyone. i have a small question, my fuel pump in my 92 camaro was hardwired when i bought it, it runs just fine just has a little problem starting, every time i start the car it will crank and crank until the check engine light comes on and then it fires, i checked it out and then injectors wont start spraying into the throttle body until the check engine light comes on, what can be done to fix this, i don't have too much knowledge about tbi, because i grew up around carbed motors, any help at all would be great, also they hardwired it by running a wire from a keyed slot in the fuse block, to one of the wires on the fuel pump, ill have some pics up asap.

Thanks in advance

 

sounds like the fuel pump is only working off the oil
pressure switch and the fuel pump relay is not working-
when the fuel pump circuit is working properly,the
fuel pump relay will power the pump when the key is
turned on and run it for a few seconds,switching off if
ECM does not get a tach signal(engine not started).
if ECM gets tach signal,the relay remains on.
As a "failsafe",the oil pressure switch will complete
the circuit and operate the fuel pump once engine has
been cranked enough to develop oil pressure

 

ok, where is the fuel pump relay, im really wanting to get rid of the wire running across my floorboard, and also the previous owner installed an aftermarket tach, its wired into the wires that run to the gauge cluster, could that be causing problems, i know when i installed a tach on my 92 s10 it told me to run a wire up to the coil.

 

I wouldn't have tapped into the gague harness for an aftermarket tach personally (I'd run a parallel wire from the coil connector in addition to the factory tach wire) but if it's done right it shouldn't cause any problems. The real problem with tach wires is if they get accidentally grounded you will get no spark at all. Doesn't sound like your problem, through.

FP relay is one of the black "cube" relays up by the power brake booster on the firewall under the hood. One is the FP relay, the other one(s) do the cooling fan(s). One fan relay with a single fan system, 2 fan relays with a dual fan system. All the relays look exactly the same, though. So just FYI.

 

Ok I just replaced the fuel pump relay today and it still wont start unless its hardwired, could there be another relay I'm missing, I noticed one was m.I.a. under the dash

 

Fuel pump relay was the one with five wires going to it right? Fan relays only have four

 

That's the one I changed.

 

Okay, cool just wanted to try and help out, but good luck with it

 

here are a couple pictures of how the hardwire was done along with one of the fuel pump relay,

 

And also just remembered, my cooling fan only works with the AC could there be any connection to those problems?

 

Well, that means your fan and relay are good. Either the fan switch or the wiring from it to the relay are not good. To check the wiring just remove the connector from the fan switch and ground it with the key on. If it works it's the fan switch. Have you checked the fuse in the little weatherpak over by the battery right in front of the radiator overflow reservoir?

 

I just did and they are all good,

 

Where is the oil pressure switch? My 85 has the pump wired into the ignition, so when the key is turned it runs with engine on or not. Would like to get it straightened out so it works as designed.

 

I'd start by checking if you still have. The pump relay hooked up, if it isn't hook it up and rewire, that's what I did to my car, my only problem now is. I have to figure out why I'm not getting any power to my fuel pump relay

 

The load side of the relay should have battery voltage (always hot). Only when the relay activates does it send that on down the line to the fuel pump. I think it gets that power from a wire down at the starter solenoid (same terminal as the big battery cable), but don't quote me on that. I'm sure somebody will chime in with the right answer.

Relay activation is accomplished by supplying it with a GROUND. The ECM supplies that ground (or the temp switch in the pass. side head in the case of the fan relay).

Also there is a SECONDARY path for power to get to the fuel pump- through the oil pressure sending unit screwed into the block above the oil filter. So either the FP relay being activated by the ECM OR the oil pressure switch closing (only requires about 5 PSI) the pump will get power. They're parallel systems.

 

The temperature switch for the fan is in the passenger side head, between # 6 & #8. It provides a ground to activate the relay and turn on the fan.

Something is odd about the SES light coming on only after it's been cranked for a while. It should turn on with a blink off at key-on, engine-off. If it doesn't check the fuse (20A) that is under the hood. Passenger side, inline with the heavy gauge wire. The wire runs from the radiator support to the firewall. It provides power for the fuel pump and the ECM.

In the case of the fuel pump relay the ECM provides +12 volts to activate it. In the TBI ECMs it is somewhat common for the small transistor that provides the power to pop. Easy to replace, can use a PN2907 or a 2N2907. It is the taller of the two in the rear corner of the PCB near the harness connector.

RBob.

 

Ill have to check that out, all my fuses check out, so that just might be my problem.

 

And also if its like mine my oil pressure switch is on the drivers side of the block just above the oil filter, your supposed to use a special socket, but a good hand with a set of vise grips can get it out

 

I just want to be clear on this issue. Is there anything that will cause a low pressure reading (10 PSI in my case) at the fuel rail besides a fuel pump? I replaced the fuel filter, and the tank is full of premium gas. I want to fix this issue as soon as I can, but have not found a clear answer.(yes I did search). I'll throw the $$ at it, if it is the problem. I'd appreciate your expert input!

 

Well from my slight knowledge there is a couple things to look at

1. Is the fuel filter on the right way, ( from what I've heard this can almost stop fuel flow) not positive on it.
2. Fuel pressure regulator could be bad, allowing pressure to be returned to the tank
3. Bad lines, leaks lose pressure
4. Fuel pump

That's all I can think of hope it helps!

 

RBob, is there any way you could provide a little more info on this please? I am also experiencing an issue with my ECM not providing +12V to the FP relay during cranking. I was looking at either replacing the ECM for about $80 or just using a jumper wire from the fuse box IGN to the FP test port on the ALDL, since otherwise it takes a squirt of starting fluid or a lot of cranking to get it started without the priming action. I'm fairly handy with electronics and soldering, has anyone done a 'How-To' on this transistor R&R?

 

UPDATE: i went to change my oil pressure switch today, got the old one out just fine but when i went to put the new one in it stripped, has anyone else had a problem with this? Also after the first two i ran a tap down it to just clean the threads it went smooth all the way, BTW im on my third pressure switch, luckily i have good friends at the part store.

 

https://www.thirdgen.org/forums/dfi-...swap-ecms.html

The picture shows a 2N2907 in place (metal can type). The PN2907 (plastic type) is easier to find. Just install it in the same orientation as the original.

RBob.

 

Well I think I may have found my problem, my Ecu looks all bubbly like it has gotten wet, I'm ordering a new one tomorrow

 

I have a quick question, will an ecm out of a 92 s10 with the 4.3 work on my 92 camaro with a 305? They both have the same transmission th700r4 same amount of injectors and all that just kinda curious if its safe to run it that way, I plugged it in and the car started, but I still need the pump hardwired

 

If you are referring to the board inside of the ECM, that is normal. They are conformal coated via being dipped into a clear liquid, and appear as though they are bubbly.

RBob.

 

It won't work correctly. The biggest issue is that the spark advance will be all wrong. The second biggest issue is that it will likely run very rich until the ECM goes into closed loop.

Replacing the fuel pump relay drive transistor is fairly easy.

RBob.

 

Well everyone I just figured out my problem and kinda feel like an idiot lol, got curious and checked what I thought was a relay turned out it was a blown fuse all along ill attach a pic of the fuse for reference when I get back on my pc

 

This is the little bugger that got me you can see where it clips in on the fender, kinda threw me off cause ive never seen this before.