Ive tried the 4th gen sites but they arent helping....and if I can figure this motor out one is going in my 84 T/A...with a 3x00 top and a turbo- gas milage SUKKZ in a Holley-carb'd V8 w/3.73's...
Ok, so I score 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. 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....

Forgot to add : NO SES LITE!!! Seafoamed the ***** 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.

 

Check the resistances of the IAT and CTS... Something may not be sending a good signal to the ECM. Also, I'd blow out the fuel lines... Who knows what crud is in there, and also change the fuel filter.

 

Forgot to add NO SES LITE, Seafoamed the ***** out of the fuel system - 3 full cans, replaced the fuel pump and filter, replaced all 3 coils & ICM with "tested good" units.....and all 6 injectors ......gonna add this info to original post. what would the proper resistance values be of the CTS and IAT be ?.....got something else to google...and wouldnt the CTS being bad result in a SES lite? and I doubt that the IAT is bad because unplugging it changes the the engine timing enough that the Popping goes away.....

 

Just because the ECM isn't posting a code doesn't mean that there isn't a messed up sensor. The resistance varies by temperature. There is a chart here that has been posted and re-posted any number of times. The best thing I can tell you is to for the chart and compare it to the readings you get from the CTS and IAT. And also measure the voltage reading coming out of the green wire at the MAP with the engine idling (if possible) or hook it to a vacuum gauge and apply a known vacuum to it with a vac pump.

 

Ok gotcha, will do in the AM... found the values in the Haynes....my manner of thinking is that since its popping back thru the intake that it HAS to be a sensor that alters timing that is bad because the engine is igniting fuel while an intake valve is open...What sensors alter timing? Do any sensor(s) affect drivability AND starting enrichment/timing? im starting to think Ive gotten a bum Fuel pump and it may be a Lean misfire...but i could be reaching here...

 

You said you unplugged the IAT and it ran better... Probably a lean misfire having something to do with the IAT. Could be it's shorted and it's affecting the TPS as well (they're on the same ground circuit).

:edit: CTS, IAT, knock sensor, 24x crank position... Well, there pretty much isn't any sensor that won't affect the timing in one way or another since the ECM uses so many input variables to determine the amount of fuel to add and when to fire the plugs.

 

Put down the ether. Not good for you or your car. So the pump was replaced and it runs like crap now? Sounds like you found the problem.

 

No, car wouldnt run at all until I replaced the pump........old Pump wouldnt prime....new pump, ran when started on ether, only primed to 10 psi and pressure leaked down to zero in about 2 seconds, so i replaced the injectors <-didnt make a bit of difference in the way the car runs, but i havent checked fuel pressure since the injector swap.

Gonna post a vid of its symptoms ASAP.

 

If it won't prime to more than 10psi and it looses pressure quickly you have a leak somewhere. Take the vac line off the fpr, turn the key to 'run' and see if you're loosing pressure there. If not double check the work on the fuel pump. If that's not it then find where fuel is actually leaking. Take the injector rail off and prime the pump. Injectors or o-rings leaking? Fuel line split? There's only a handfull of places it could be loosing pressure.

 

I cant find a fuel leak anywhere, thats the reason i swapped injectors, I figured i had one stuck open.....and I replaced the FPR when I did the injector swap, I havent rechecked the fuel pressure since, but I did stick a piece of hose up my nose and did a "sniff test" to see if i could smell any fuel and i couldnt - i was paraniod about o rings leaking and setting my car ablaze....Im starting to think I need to recheck the Fuel pressure as i may have gotten a pump with a bad check valve.....And I will stress again that I did a Fuel pressure check AFTER i replaced the pump, but BEFORE I replaced the injectors and FPR, but havent checked it since because I returned the FP test gauge to get my $100 back...time to "rent" another.....

Oh and BL85C ur car is Badass....its THE reason I got a 3400 UIM & LIM.....Now I just need 3500 heads and a way to tune obd 1.5 I want a fast V6.....And while Ive got ur attention will 3500 heads work with a 3400 LIM? some say yes, some say no..

 

There is a common problem that occurs when the pump is replaced... Sometimes the line between the pump and the sending unit pipe cracks and breaks. You'll need to get or make some fuel hose clamps and clamp off the fuel lines one at a time after you get the pressure gauge (I bought the $50 Actron one).

Oh, and you CANNOT tune OBD 1.5... Even the experts on 60degreeV6 won't touch those monstrosities (there is no hack for any of them). They generally swap in the 16149396 or the 1227727 in place of the OBD 1.5 ECM when they want to tune.

 

You should use a 3500 lower. I'm looking at some 3500 heads myself right now. If I started this build over again I'd definately go with the extra breathing the 3500 heads would give me. 3400 heads are fine with some work, but I'm probably loosing out on another 10-20hp without them. And thanks for the comments. Like Maverick H1L said, double check your pump.

 

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!

 

Will it start easier if you 'clear flood' (hold the pedal to the floor and release while cranking)?

 

Havent tried.....But I will in the morning....I think I see where u are going with this and I cant believe I didnt think of it before now....say it does, what then?

 

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!

 

Glad you got it running. The check valve in the defective fuel pump would have been the next guess (supposed to allow fuel only OUT of the tank and not back in again to hold the fuel pressure for next engine start).

 

Great thread. Glad it's running. I have the popping/backfiring issue with my son's 88 2.8. Anyone have an answer why replacing the fuel pump fixed it here. I don't have much history on my boy's car and have no idea what has been done to it other than what we have done to it.

 

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