Hey everyone, I am new to the Firebird scene and could really use some help with a problem I am having. About a month ago I purchased a 1989 Firebird with the 305 V8 and automatic transmission. The car would not start when I bought it, but I knew how to fix that. I put in a new starter solenoid and a new battery and it cranked right up. The bad news is that it will not stay running. It sat for over a year before I got my hands on it.

What it's doing is it will start fine and idle around 1000 rpms for a second or two. Then the rpms will drop down to around 100 and it will either stall out or it will rev back up to around 1000 rmps and then idle down again and stall. If I touch the gas at all during this period the car will try to stall even faster, but when I take my foot back off of the gas the car will rev back up again.

I have replaced the battery, starter solenoid, spark plugs, fuel filter, I drained the old gas and added new gas. I have cleaned the injectors, replaced the fuel pressure regulator, vaccum checked and fuel pressure checked the car.

I am at a loss on this one. I am unfamiliar with this TBI setup. I usually work on MPFI vehicles. I have had someone suggest possible problems being at the IAC or the TPS. Any help would be greatly appreciated.

 

Welcome TGO1) Do you see 13 PSI FP at all times??? If you still have original FP the chances are that FP is very tired.//RF

 

I just checked the TPS as outlined here https://www.thirdgen.org/tpimod2

I used the jumper wire and VOM method. I could not get any voltage reading at all. Does that mean the TPS is totally dead or am I looking at a wiring issue?

 

I just got back in from checking the fuel pressure. Fuel pressure is at 3 psi. Thats bad! Additionally, the 3 psi isn't even constant. 3 psi is when the ignition is first turned on and when the engine is turning over. There is 0 psi within seconds of letting it sit. I know it is not the fuel pressure regulator, the fuel filter, or the throttle body, since I just serviced all of that. Does that just leave me with the fuel pump as the problem? Also, I still have no clue what is going on with the TPS. Any suggestions or comments would be great. Thanks.

 

1989bird'

1) Fuel pump must be replaced. The problem the bugger is inside gas tank. FP replacement is the least of my favorite things to do. Remove as much gas as possible from tank before dropping it. Get a quality unit (FP), also replace fuel sock and in tank fuel hose. Replace fuel filter.

2) TPS can be checked with a DVM. With Key on - engine off back-probe each pin on the TPS connector, throttle at idle.

Pin A (Gray wire) + 5Vdc
Pin B (Black Wire) 0 Vdc (Ground reference )
Pin C (Dark Blue) 0.5 to 0.6 Vdc (TPS output)

Slowly advance throttle from idle position to WOT position - DVM reading at Pin C must smoothly increase from 0.5 V to about 4.8 Vdc at WOT position. Any sudden drops, jumps, etc indicate that TPS must be replaced.

I hope this helps

//RF

 

Thanks for the advice. I am double checking all of the fuel system to make sure that the problem is actually the fuel pump before I go through the pain of changing that out.

Also, the TPS is not bad. My brand new VOM is bad. I got out my old piece of junk VOM to double check the TPS and it is good. .68V at idle and 4.3V at WOT. The .68V at idle sounds a little high based on the spec of 0.54Volts +/- 0.075Volts, but I don't think it is enough out to cause a problem.

Anyhow, I am really not looking forward to changing out that fuel pump. Does anyone have any suggestions or personal knowledge that they would like to share with me that might make the process go easier?

 

Just for the heck of it I listened through the filler pipe into the gas tank to hear what the fuel pump sounds like. The pump comes on when the ignition is turned on and cuts off when the relay clicks. That part I know is right. What has me puzzled is that after the relay clicks and the pump shuts off, I hear gas running off of something and into the rest of the gas (that sounds like water running off of something into a pool of more water... except in a gas tank). I know that there is very little gas in the tank, but should it be making that sound? I am sure that either way, I am going to have to pull the fuel tank to see what the problem is. And as long as I am already pulling the fuel tank I will certainly be replacing the fuel pump. I just like to know whats going on before I get ***** deep into a project. Thanks again guys.

 

'bird305

ECM during key on sequence will turn on FP for about 2 seconds and then will turn it off, until engine is cranking.

You can check fuel pump functionality by bypassing FP relay. Warning - you are working on high pressure fuel system - take appropriate precautions. Look at FP relay socket - on some cars it should have a red wire or gray wire 4" pig tail attached to it. If it does not get a sufficient length of #12 AWG wire jumper wire between the fuel pump side of the FP relay socket (gray wire) and battery positive terminal. This connection will force FP to run continuously regardless - hence warning. If you hear FP going out - well you got four days during coming up to replace it.

//RF

 

Thanks for the tip. I will check that out the next chance I get. Unfortunately, I work in a field that operates 365 and I'll be working while everyone else is enjoying a couple of days off.

 

Let us know if you need any other tips - be well...

//RF

 

Just wanted to do an update and end this thread. I got my Firebird back from the shop today after having the fuel pump replaced and she runs like a dream. The rubber hose that carries the fuel from the pump to the steel lines was dry rotted. This caused most of the fuel to just pump back into the tank rather than down the lines. The fuel pump eventually burned itself out trying to keep up.

Thanks for all of the help.