I swear I am ready for a carb.

1985 Corvette put in a new Fuel sending unit (new not used)

Same pump The damn thing never want5s to start when the temp is cold BUT NOW

When i start I am now getting about 25lbs after turning the key off then it drops back to 0 very fast.

Any ideas.. beside a carb conversion.

 

leaking injector?

 

I think this will help you....

••••• TESTING FOR LOSS OF FUEL PRESSURE

... Here are the sure fail tests for the fuel system to save you time and money.. Take a fuel pressure gauge attach it to the Schrader valve.. Turn the key on and off a few times to build up the pressure in the system... If you are having starting trouble the pressure will probably drop as soon as it hits 38 or 40 and the pump turns off it will probably leak back to zero within a few minutes. Ok now right after you prime the system pinch off the return line near the tank if the pressure drop stops it is a bad fuel pressure regulator.... Next pinch off the feed line if the pressure holds then the leak is before the point where you pinched the line IE fuel pump check valve..hole in the metal line on the sending unit caused by it rubbing on the inside of the tank you should visibly be able to see this if you pull the pump and the sending unit...(this was my problem) or the pulse dampener which is the piece between the pump and metal line on the sending unit.. the diaphragm tears.. and last if you pinch both the feed and return line near the tank and the leak down of the pressure continues then a fuel injector is your problem.. This is the GM test.. saves time and money..
•• disconnect the vacuum line from fuel pressure regulator

 

Replace and tighten the clamp that attaches the fuel pump to the fuel line.

 

Whats that got to do with the TPI?

A carb isn't going to fix a bad check valve in a fuel pump. Fuel pressure that bleeds down quickly is from 1 of 2 places...

the fuel pump line inside the tank, or the fuel pump itself. <-usual problem.

 

The fuel Pump is a couple years old and like i said i just replaced the fuel sending unit today. Im pretty damn sick of this entire TPI mess. EGR, IAC, TPS, Fuel pressure regulator, Cold start injectors and so on. it has been one damn problem after another. I know its 28 yo technology. Just getting real tired of chasing fuel problems.

Thanks for all the advice i will be banging my head against the wall in the garage for a few weeks im sure

 

I also failed to mention I did not put the Fuel Pump Pulsator Dampener back in. the new FSU came with a hose instead of the Fuel Pump Pulsator Dampener. I wonder if this is where my problem lies? When i hear the pump shut off the pressure immediately drops.

Does any one have experience with this?

 

The lack of a fuel pump pulsator dampener would not cause the problem. If the hose that you replaced this with had come loose, that could be the problem. If you put the hose on with claps....you can eliminate that as a cause then. The pulsator acts like a balloon and inflates when the pump pumps. As the pump starts to cycle into its next pump, the pulsator starts to deflate. The idea is to try and keep a constant pressure instead of a pulse.

How long does it take for the pressure to drop back to zero? If it is almost immediately then I would look at the pump check valve. Longer could be a bad injector or FPR diaphragm. Run the test above and that will narrow it down for you.

 

Its immediately and thanks you I am also having issues with my fuel gauge (i have a after market) boy how i have missed Corvette Mystery Theater

 

Follow his steps get a clamp or vice grips to clamp the fuel return hose at the fuel pump/sender connections.
Clamp the rubber return connector hose and check what the fuel pressure does, then get a friend to turn ignition on and off and clamp the fuel supply hose the instant the pump turns off.
If the pressure still drops at the fuel rail on engine disconnect the injector electrical connectors (As well as the cold start injector) and release the fuel supply clamp and repeat run injector and clamp it of the instant the pump stops. if you are still loosing pressure then get your injectors tested (including the cold start one)

You may only get 30 psi which is normal as the 85 came with 24lb injectors standard, that was all my standard fuel pressure regulator would supply.
I fitted an aftermarket adjustable one and set to 45 psi ... now your TPI will love that

I had only two fuel issues with my 85 vette over the last 16 years, one was a pump died the other was a bad injector electrical connector causing a miss.
I have put over 100,000 miles on my 85 they are very reliable,
You do not want a bucket with a hole (carburettor) and loose the easy start cold or hot the smooth idle and performance with great fuel economy.

 

You may only get 30 psi which is normal as the 85 came with 24lb injectors standard, that was all my standard fuel pressure regulator would supply.
I fitted an aftermarket adjustable one and set to 45 psi ... now your TPI will love that

I had only two fuel issues with my 85 vette over the last 16 years, one was a pump died the other was a bad injector electrical connector causing a miss.
I have put over 100,000 miles on my 85 they are very reliable,
You do not want a bucket with a hole (carburettor) and loose the easy start cold or hot the smooth idle and performance with great fuel economy.[/QUOTE]



I am kicking and dragging about the carb I have had them in the past and im not a fan but this TPI has been worse. I have a new EGR Valve on its way. Do I need to clamp the hose that comes from the fuel pump? I did not do that when i replaced the Fuel pulse diaphragm.


May be time to call in The master (Danny Popp) and have him give it a once over from top to bottom.

 

If you did not clamp the hose that replaced the pulsator it probably blew right off again. Check that first and put clamps on it, then do what John A. Marker outlined in his post to absolutely identify the cause of pressure loss. Mine ended up being the base of the fuel pressure regulator, the diaphragm was not sealing against it. If I had not heard of the testing procedure I would still be looking for that leak.

 

Do you mean the disc that seats against the bottom?
I've seen that leak fuel straight to the return system where the loss goes unnoticed. The only symptom might be hard starts or unexplained bleed down. It tends to pressurize the return side a little so the pressures are near equalized....so its not seen so easily on the test gauge. But, half the fuel is going back to tank instead of being held under tension in the rails to go to injectors as needed.
Clamping the return hose somewhere will help to ID the problem. pressure should build, then STAY for hours. if it does not, then you look at whatever is between the pump and your clamp and a place where that pressure could escape. It has to have a way back to the tank or out of the system...if its thru injectors the cyl will be wet.

 

Carbs are 100 year old technology. Just sayin'.

 

I was having pressure drop off on my 85 that I noticed after I changed the injectors (that eliminated the leaking injector cause). It turned out that my fuel pump was the cause. I replaced the pump and the pulsator and it held pressure overnight into the next day where before it would bleed off in a half hour. You should also check your fuel pressure regulator. Look to see if there's fuel in the vacuum hose.

Did you say you're replacing your EGR valve? If so, be careful not to damage the sensor that's screws into the base of the valve. They are discontinued and if you do locate one, they run from $75 up to $100.

 

Yep, that's exactly where it was losing pressure, took me forever to track that one down. I'm sitting here trying to remember what issue I was having (other then pressure loss) but I am not having any luck. I do remember that when I replaced the base the problem disappeared.

 

Ahh i live for this stuff. I appreciate all the great advice. Im pretty frustrated so i will work on it Sunday again I am pulling the FSU again clamping the new hose an starting from there. I replaced the following parts in the last 3 years

Fuel Pump
FSU
Fuel Filter
Fuel pressure regulator
IAC
TPS
I have printed out the test and also will be tracing and fixing vaccum lines.

 

Thank you know I know i will muck that up.

I may replace the Fuel pump regardless its a cheapie auto zone one that i had to buy on the road in cleveland. I need to upgrade to a ac delco.

 

My TPI motor runs amazing. The torque is just incredible.
and it looks prettier than todays plastic motors. In fact the TPI runners still look sexier than any other motor I have ever seen.