3.4: wont start without ether,backfire thru intake

[RedRokkit]

Ok, so I scored a 94 Firebird for $200....owner was a good friends In-Law and died from cancer and they just wanted it to go to a friend who would treasure it like the PO did...They said about him "some people have children, Rob had a Firebird". It only has 93,000 miles on it and it was expertly maintained and I have a ton of maitenence/repair info on it. It was running and driving when he parked it in 2007 and after a fuel pump swap and drain and cleaning of the gas tank, and a minor VATS issue it is running again....somewhat....It wont start - especially when cold without a GOOD spray of starter fluid, after its hot, it will sometimes start fine on the first try, sometimes it takes several attempts, but it will start after warm without fluid...WTF!?! And once it starts it has a stumble/pop/ Backfire condition off idle, that is most evident at about 1200-1500 rpms, but will happen at other rpms as well.....the car is bone stock and was running perfect when parked....I had the fuel pressure tested and it wouldnt hold over 10psi and would drain down in less than a second...So I replaced the FPR and fuel injectors($ouch$) havent tested FP since ($30 at a shop). The only thing that I can think of is some sensor is bad, but where to start...... and another curious thing is that if I unplug the IAT sensor, the stumble all but disappears?!? any insite to this problem is greatly appreciated....

[60dgrzbelow0]

Well... God Rest the PO's sweet soul...but it seems like for the time prior to his death...the car may have sat too long and the fuel is either stale or "scrabnoid" with gunk and water. It might be a good idea to move the vehicle away form the house (no smoking, flames or sparks, please...have a fire extinguisher on hand as well) and connect a Schraeder fitted fuel line to the Fuel Pressure Service port located on the top front of the Fuel Rail Manifold. Now, snake that long fuel line down inside of one or several large gas cans as needed and drain the fuel almost dry from the the tank. You will need to have a friend watching how how much fuel is being pumped out with instructions to yell, "STOP!" before the collection tank(s) overflow.

When you turn the ignition key to the service position on the steering column... but no further...you should hear the electric fuel pump whine. Watch the fuel gauge and see if the level drops bit by bit. Listen very carefully for the sound of the electric motor suddenly increasing in sound pitch... this might indicate that the tank is dry or getting close to being completely evacuated. SHUT OFF THE IGNITION BEFORE YOU RUN THE RISK OF BURNING UP THE FUEL PUMP! The electric fuel pump in your FB is very durable...but it uses the fuel it pumps to also cool and protect the pump motor as well. If you run the tank too dry...you could damage the pump and make this problem get even more complicated. Since you are not the original owner... you might find out the the PO installed an external after-market fuel pump that is not operating properly. Look under the vehicle adjacent the front bottom of the tank for any bolt on pump(s).

As soon as this is safely done, immediately pour in about 5 gallons of fresh, high test gas and squeeze in a large bottle of Chevron Techron as well and try to start the car. If the Firebird gets up and running ...relax and let the engine idle and warm up for a few minutes while the system studies itself and the ECM adjusts to whatever the O2 sensors are telling it based on the new fuel being burned. If it idles fine for a while, gradually raise the RPM a few times and then take it for a drive around the block to see how the engine responds under loading. (Not Racing!)

You don't mention whether or not you either changed, gapped or cleaned the old spark plugs in this motor. If the gas drain-re-fill technique does not show a distinct improvement... get the Haynes Manual for this car and open it to the back pages to find "The Spark Plug Chart"...pull the plugs one at a time and be prepared to eyeball them against the chart to look for any weird symptoms that would indicate bad valves ...or worn rings, and the resulting lowered compression. Don't forget to check the electrical connectors on the ICM and the spark plug wires attached to the three-coil pack for solid connections. If after changing the plugs...the engine still sputters and misfires, pull all the plugs and perform both a wet and dry compression test to identify any cylinders with poor compression... gas cannot ignite and burn properly without the right range of compression. ...and by all means... then tell us what happens, please.

[RedRokkit]

Forgot to add : NO SES LITE!!! drained & Seafoamed the Shite out of the fuel system - 3 full cans - half a can at a time with 93 octane, replaced the fuel filter, replaced all 3 coils & ICM with "tested good" units.....and all 6 injectors.

[bszopi]

I think the second to last sentence in your original post should sum things up...

and another curious thing is that if I unplug the IAT sensor, the stumble all but disappears?!?

Have you thought about replacing this with a quality unit? They are cheap enough, I would try to go with an AC Delco unit. But either way, it would be a good place to start, as a bad IAT sensor will cause the ECM to do some wierd things.

[RedRokkit]

Its on my list but would a bad IAT cause a no start/ hard start condition? Im starting to think I may have a bum check valve in the fuel pump.......I REALLY need to check the fp again ..and unplugging the sensor may alieviate the stumble /misfire/popping, it wont start any easier when i disconnect it

[RedRokkit]

OK guys heres a vid of it in park revvin' it in the garage: http://www.youtube.com/watch?v=ZCa9iFKonyw

Its popping back thru the intake but i can also hear dull pops under the passenger floor near the cat.....like unburnt fuel is getting ignited by the cat.... and its still hard to start.

and please ignore the stoner drawl DOODS!

[pocket-rocket]

I almost think timing, stuck injector or bad ICM. Where are you located?

[geoffinbc]

Sounds like timing. I bet the plug leads on the coil packs are in the wrong position

[RedRokkit]

Richmond, VA BUH-DEE

injectors and ICM been replaced since i got it...thats what I thought too...Definitely sounds like timming..and its definitely popping back thru the intake , you can feel it if you pull the duct and put your hand in front of it....

[RedRokkit]

Sounds like timing. I bet the plug leads on the coil packs are in the wrong position

Double checked it when I replaced the coils& ICM...But since its free Ill check again..

[geoffinbc]

And it was working fine before that? Ignore any numbers that may be on the coil packs. They can easily be shuffled around. Find a manual illustrating the proper arrangement. A quick check without a diagram is to make sure 1-4, 2-5, 3-6 are sharing one coil pack. These are the companion cylinders. So if plug 1 is sharing a pack with plug 5 then its wrong no matter where it sits.

[RedRokkit]

Well friday got here finally and I had some $$ and time to work on the car some more....Tried the "clear flood" suggestion and it wouldnt start at all, so my mind thought -" if its not flooding, it must be starving for fuel....so I bit the bullet and bought a FP test gauge...and what do you know, the new fuel pump would only prime to about 25psi and immediatly drop down to Zero on the gauge...HMMMM...so i figured its time to check for fuel leaks and I found no leaky injectors, no leaks at the fuel filter, no leaks at the rail and no leaks at the lines or connections anywhere in or out of the tank..... WTF !!! So I figure WTH, and yank the pump and take it back to VATOzone and ask for a new pump because this one MAY/MAY NOT be bad, just to be told that electrical parts are not returnable. great so after Politely Reasoning , then alot of cussing I walk out of there with the same pump and a refusal to EVER give them my business again....So now I am even doubting that the pump is bad and thinking of putting it back in the car when I see that I have enough time to see if the Junkyard has any 4th gen fbodies....WTH, it will at least tell me if the pump is bad or not rite? Not only do they have SEVERAL 3rds and 4ths but they had a 94!! So an hour later Ive got my $16 "new" pump in the tank (FP access panel - FTW!!)...and she fires rite up on the first key!!!! So I let it idle for about 15 minutes and then I take it for a spin, and lemme tell you it was almost worth all the frustration and $$ misspent due to a crappy "new" aftermarket pump.... So all thats is left to say is


Thank You Brian And Chelsa!!
You thought of me and now the Bird has got his wings back and we will be soarin.....Heres to you Rob Hayes... Your Bird is in good hands....My wifes...LOL!

[geoffinbc]

Make those bastards give you your money back!

Not sure how it works in the States but in Canada you can return any defective product within one year at the point of sale under the Canadian Consumer Protection Act.

[RedRokkit]

Make those bastards give you your money back!

Not sure how it works in the States but in Canada you can return any defective product within one year at the point of sale under the Canadian Consumer Protection Act.

I think it was the fact that I tried to return it in a "BAD" part of Richmond VA.....and they probobly deal with more that a few scammers on a daily basis.....I took it to a "better" part of town and BAM Had my $$ back in 10 mins....

[geoffinbc]

Good deal.