joe69formula

Hello, I have a 92 Formula 305 TBI with hesitation. I bought the car in Maryland in May. It ran fine up until a couple of weeks ago.

When I start the car ( cold or hot) , it loads up then wants to stall , then repeats the cycle. I get the hesitation at idle and sometimes while driving it. I read the link below and some have suggested to replace the TPS (Throttle Position Sensor).

https://www.thirdgen.org/forums/tech...nly-under.html

I replaced the TPS, coolant temp sensor, air cleaner, breather and some vacumm hoses today. Still have the hesitation.

The plugs, wires and cap/rotor seem fine.

Items that have not been replaced:
a) plugs, wires and cap/rotor
b) fuel filter
c) MAP Sensor
d) Inlet Air Sensor

Does the TPS have to be adjusted?
From what i read, some earlier TBI cars had to be adjusted, but for the 92, it does not seem to be the case.

Is there any thing the would cause theses symtoms?

Thanks

joe69formula

I took the air cleaner off today to check out the vacuum lines. I noticed that the base for the air cleaner had a gasket sticking out of it (between the air cleaner base and the throttle body). So, I decided to take the base off.
There was a gasket that was worn and bulging out of form, letting in excess air !!!
Shown in the pic below:


So I found a gasket from my pile of Quadrajet carb parts from my 69 GTO:



Here is the base for the air cleaner:



Here is a pic of the thickness between the two: ( not the best pic)



Here is the gasket on the throttle body:


... and the base on the gasket/throttle body:



I took the car for a drive and this seemed to stop 95% plus of the hesitation.
When i first started the car, it would go up to idle , then drop down, then up to idle again. This cycle repeated a few times until the car warmed up.

joe69formula

I checked the EGR and vacuum line going to it. With the car at operating temperature, I disconnected the vacuum line and hooked up a vacuum gauge to the line. The gauge read 8-10 Hg as I moved the throttle. Then i connected the line to the EGR valve and moved the throttle, the EGR diaphragm did not move. SO I need a new EGR.

Would the EGR alone, cause the idle to rise then drop ? ( this occurs in a cycle )

joe69formula

Update:
The car still hesitates, especially when it is cold. When the car has sat for a while, it will start, idle fine for a minute, then the idle will start to surge up and down (load up/down) until the it is at operating temp.

I have replaced:
- Idle Air Control valve ( made an improvement )
- TPS ( made an improvement )
- coolant temp sensor ( no improvement )
- EGR valve ( no improvement )
- fuel relay/oil pressure switch, but did not install it yet.

First thing to point out is that the oil pressure gauge is pinned to the right. Not sure if the fuel relay/oil pressure switch would do it.

Second, the fuel pressure is at 8psi (reading taken from the fuel line connections on the left of the engine). The chiltons manual states that it should be 9-11 psi. The fuel pump does make a louder noise when first turned on compared to what i heard from other f-bodys.

Third, the previous owner put a 2.5 or 3 inch exhaust.

Fourth, I checked and replaced some dry-rotted vacumm hoses.

Fifth, I checked the spray pattern of the injectors. They have a solid cone spray pattern. More liquidity than a mist.

ex-x-fire

Sound like the pump is weak, hook a gauge up to it, tape it to the windshield, drive it till it acts up.
Are you running a stock air cleaner or an open element?

joe69formula

I am running a stock air cleaner. The car doesn't look like its been touched in the engine compartment. It still has the original date coded coolant hoses.

dimented24x7

iTrader: (2)

The fuel pump is shot. Should be at least 10 PSI or so. Closer to 12. Youll need a new one. A TPI pump will work well if you plan on future mods.

rgarcia63

The EGR & IAC passages probably need cleaning.

The Exhaust Gas is only used at part throttle about 2000 rpm (controlled via the EGR solenoid) at that engine speed manifold vacuum is to low to operate the EGR valve properly so ported vacuum is used, that's vacuum produced above the throttle blade not below it which is manifold vacuum.

joe69formula

Well, it's been a while since my last post. But the problem is fixed!!!! It was the fuel pump hose connecting the fuel pump to the fuel sending unit.
The hose was split length wise.

The fuel pressure reading was 8 psi before and 12-13 psi after (at idle) the fix. It goes up to 14 psi when i move the throttle (while car is in park).

I seen this done on the turbobuick website, but the link is invalid:
http://www.turbobuick.com/forums/tur...utes-less.html

Here are some pics to show how i did it:
I bought an air nibbler from Harbor Freight tools. They have decent tools at great prices. The air nibbler cost $25.


I cut the fuel lines using a brake tube cutter (cut by hand). NEVER use a power tool on the fuel lines or you will blow yourself up!!!!!

I used compression fittings on the first two lines from the left of the fuel sending unit, shown in this picture. The first is the supply line to the TBI, the second is the return, the third line i'm not sure yet, and the fourth is for venting.

joe69formula

Here is the fuel pressure gauge i bought. Forgot where i got it from.


Here is the adapter connected inline, next to the alternator:


And here is the finished product:


Today, i drove it for a long drive to work( 70 miles round trip). So far, i used 1/3 of a tank of gas and got 107 miles so far. The throttle response was awesome!!! There is no rattling of metal in the back. The compression fittings mentioned above are 3/8" and 5/16" from Pep Boys. One thing to mention, take out the fuel sending unit assembly out carefully!!! The one in the picture above was the original one. I broke the fuel level contact inside the fuel level housing. Nothing was touching the variable resistor in the fuel level housing and the fuel gauge needle was pinned past the full mark. So I bought a new Spectra fuel sending unit assembly from Pep Boys for $170, along with a new Carter fuel pump.

Some people will not agree with this method. I does work, looks professional and no leaks!!! In the past two and a half weeks, my daily driver died (94 Ranger), bought a new car, then my wifes 2000 Exploder (explorer) blew the reverse band in the transmission at 108,000 miles. We had that exploder since it was new. What a piece of crap!!! Anyway, i needed a driver, and this solution worked out. I hope someone finds this helpful. Thanks to all that have responded to this post !!!

ex-x-fire

Looks like a good repair to me.
I think its funny when are concerned about those access holes weakening the body, but I feel the sameway about when gm istalled t tops on them.

joe69formula

Thanks for the comment. I used 14 gauge steel from Lowes for the cover plate. I then trimmed it with the air nibbler, then marked and drilled 10 holes for the 6mm screws, that connect to U-nuts. These are available at the local Ace hardware. I then cut a couple sheets of rubber (used for bathroom shower installs) for sealing. I layered them for a better seal. If i had time to order PEM fasteners or some type of self-clinching fasteners, then i could have only used one sheet of rubber instead of three. I might do that in the future for a cleaner install.