Hey guys, past couple of days it's been really tough to get my 305 tpi to start. Either I start it up, it idles for a second, and then drops in rpm rapidly and goes up and down and then dies. Or it just takes 3 or 4 long starts and then it will fire up. Looking for suggestions if anyone can give any.

 

I had a similar issue and found a fuel leak at the rail. Couldn't hold pressure.

This isn't the only thing that effects the ability to start up and idle, but it was mine. Check your fuel pressure Key On Engine Off, then turn the key off and observe leak down. Pressure decay should be minimal over a short period of time. If it immediately starts dropping, you have a leak, faulty FPR, or leaking injectors.

 

Engine off key on I get no fuel pressure reading.

 

 

I can hear it prime. The fuel pressure gauge goes up a tiny bit, not even to the white line though. When it's not warm it reads 55-60 when running and 35-45 warm depending on rpm.

 

 

I think Tuned Performance pretty well covered it, the only other thing I can think of is the pump has a check valve in it, if that is bad the fuel will drain back into the tank through the pump when the pump is off.

When you crank the car does it fire off quickly or do you spin the starter for several seconds before it fires off?

So you obviously have a fuel delivery issue, but your initial symptom could also be the IAC also, it just lead you to discover the fuel delivery issue. (fix the fuel but don't be surprised if you also need to replace the IAC)

 

Is this right? I have never heard hot and cold affecting fuel pressure? RPM yes. Also 55-60 sounds too high especially with stock 19lb injectors.

 

When I crank it takes up to 5-6 seconds before it fires up. Yeah I thought 50-60 was high also, I've only ever seen people from 30-45 from what I've read on the forms. I'll try tuned Performance'' suggestions and see what happens. Thanks for the help!

 

Are you really seeing 50-60? Wow! I have never seen anyone report it being that high. If you have both High/Low pressure problems, I would think that would lead me to think FPR issue. I will be watching to see what resolution comes from this, it's a new one.

 

 

I'll try to upload a picture of the gauge today.

 

Also, if this makes sense to anybody else out there codes 33-34 pop up after a long start up process, 5-6 seconds, but don't pop up on the rare occurrence of a clean 1-2 second crank.

 

 

Ok, any recommended ECM replacements Tuned Performance? I assume some are better than others.

 

 

Just replaced the cat a month ago with a Magnaflow. Old one was completely broken, it was basically just rocks. It increased performance heavily but didn't erase the codes.

 

 

This is the reading at 800 rpm idle after it wasn't started for 4 hours. Eventually went back down to 35 after abiut 30 minutes of running. It's sitting at about 50 psi. Just thought you guys would be interested to see.

 

That's oil pressure not fuel pressure. Still to high but probably sender though.

Ironically the fuel pump engage circuit goes through the oil pressure sender.

You will need to buy a fuel pressure gauge there isn't one built into the car.

 

Ok, that makes sense. I've been saying fuel pressure this whole time but I meant oil pressure. My bad.

 

It does not. This is an old misconception.

The sender unit goes to the dash - this is the one by the distributor..

The Switch goes to the fuel pump and is a secondary switched power source. As Tuned Performance stated above, it can be jumped to provide power to the pump all the time... it can not break the circuit from the relay to the pump.

Here is a schematic.

 

Depends on the year, 89 firebird uses a 3 wire sender that feeds the gauge and the pump. I know this sender well I've replaced it 3 times over the 22 years I've owned the car, not from failing to work but starting to leak out of the end.

I was a little loose on my terminology and assumed the 88 was the same as I was typing on my phone. My point is if the ECM isn't triggering the fuel pump, if you spin the starter long enough to build oil pressure the car will crank because the oil switch will power the pump (I know this from experience) but when the engine is hot you can't build enough pressure with the starter (again experience).

I didn't mean to say if no oil pressure then it will kill the fuel pump. However since he wasn't reporting fuel pressure readings to us, and the pump is priming with the key on, this is probably not the case.

 

As you can see on the TPI schematic I posted, the oil switch is a bypass around the relay, it doesn't trigger the relay.

What engine was in your 88 Firebird? I would like the see the schematic that shows this. I was under the impression at one time that the oil pressure switch could break the fuel pump power supply - Either because it passed through it, or after the prime cycle the pressure switch closed the relay and thus no oil pressure would open the relay and shut off the pump. I have since learned it does not but it was said on here for decades.... yes I have been around here since the black and green days in the 90s... but have only dealt with fuel supply issues on TPIs. Other systems could be different.

On the schematic, the ECM, Oil Pressure Switch (not a sending unit), or the relay can supply power to the pump. I imagine this is because the ECM is no set up to constantly supply the amperage needed to run the fuel pump. The oil pressure switch is a fail safe. This is my reasoning, I may be off.

 

Looking the change over is 88 and older, you have separate oil sender and a oil switch. 89 and newer you have a combo oil sender/switch that is above the oil filter. The latter model (1989 and newer Firebird it may be different on the chevy as new changes were often done different years on the Pontiac or the Chevy) has 3 wires 12v+, gauge, pump (I corrected my statement above it feeds 12+ directly to the pump bypassing the relay). I've only ever worked on 89-92 models so I didn't realize the 88 and older v8s a separate oil switch and sender. -- so since the OP has an 88 your schematic is correct. I know the difference between the switch and the sender but I tend to use sender in the general term (on/off is still technically a sender it just has two values not a range)... may not be ASE but a square is a rectangle but not all rectangles are squares.

But --- back to the original issue.

88formula5spd your pump primes (or at least you hear the noise) so that makes me think your pump wiring is intact and working. Can you confirm engine off, move key from off to run (but not crank) you hear the fuel pump kick in for a few seconds and then back off?
I would get a fuel pressure gauges and see the pressures.
My gut says the symptoms are more than likely a failing fuel pump, check valve, regulator, or other fault causing low fuel pressure or idle air control valve, but I hate just throwing parts at the problem. (the crank then die says IAC, the takes several times says a fuel pressure issue)

Really your option is to buy or rent a fuel pressure gauge and diagnose the problem, take it to a mechanic to diagnose it, or replace a bunch of parts until you get the right one ...

 

Hold up, when people search these issues, the thread discussions become important, and misinformation can be detrimental to members.... A sending unit sends a signal that then gets interpreted ... a switch is on/of. The switch is not sending anything anywhere in the schematic above, is it closing a circuit. This is not a square/rectangle thing... it is a square and triangle. Even if a switch is monitored it is still a switch closing a circuit, a sending unit does not do this, it monitors the circuit only. Different functions.

Also, what revisions are you speaking of when referring to the Camaro/Firebird that happened in different years. They were always produced together and on the same lines. I am not aware of this, unless it specifically referring to options. Certainly not a wiring harness and since they went to common motors, The LB9/L98/LT1/LS1 all became available in the same model years.

I need to see a schematic. Here is one claimed to be from and 91 Camaro. It shows a "Fule Pump/Oil Pressure Switch", a "Fuel Pump Relay" and the line from the ECM. This is not showing any wires going elsewhere to also be the sending unit. I am not saying you are wrong, I just want to see it because I have never worked on one that was set the way you say... but I have not owned all years from 82-92. I just want to know and make sure the information shared here is accurate to the next guy who finds this thread to fix his car. Unless someone can show me otherwise, I believe them to all have a sending unit and oil pressure switch for the fuel pump circuit. I may be wrong, but I want to know for sure. This does not show wires going anything dash related, so it may just be omitted. Honestly, I want to know if it was changed but I need some sort of documentation.

Claimed 1991 Schematic:

 

Sounds good Aviator 857, I found a couple of fuel pressure gauges for cheap on Amazon, I think I'll invest in one of those and see where it takes me. Thanks for the help.

 

The schematic will show the oil switch, my point is on a 89 lo3 firebird and newer, and I believe all V8s of that year and newer there is no oil detection device behind the distributor. There is a block off plug there on most of the ones I've seen. The schematic only shows the circuit not equipment placement so it's not the full picture. The oil switch and the oil sender is combined into a single piece of equipment that is above the oil filter. This sender/switch combination does both the fuel pump circuit and the oil gauge. It has three wires. A 12+, gauge, fuel pump feed.

Where as 88 and older has two separate pieces of equipment a switch and a sender. One has a 12v and fuel pump feed wire, the other has a wire that goes to the gauge.

I only know the Pontiac well enough to state with certainty that 89 was the change over year, Chevrolet was probably the same but can't say for certain.

We just have to agree to disagree on if a oil switch is technically still a sender, but since it's a combination part on my car who's primary function is to drive the gauge and secondly to backup the fuel pump circuit I call it a sender.

 

you can get a free one at Autozone as a loan a tool.

 

The oil pressure switch for the fuel pump circuit, regardless of where it was located, would provide power to the fuel pump once oil pressure reached a threshold value. This is an independent circuit from the fuel pump relay, and is only there to provide an alternate power source for the pump, should the primary circuit (relay) fail. So, if the relay fails, it will still start, if you continue cranking long enough for oil pressure to come up.