I checked the fuel pressure on my89 iroc 305 tpi to trouble shoot some problems and found that I only had 10 pounds of pressure at the fuel rail. I know that is way to low. The car has a new fuel filter, and was supposed to have a new pump. My question is when you turn the key to the on pos. the fuel pump run for about 5 seconds and shuts down like it is supposed to, what makes the pump shut down does it hit a given pressure before it shuts down or does it shut down after a certian amount of time? Any input would help me in diagnosing if the pump is bad or if I have a blockage in the line somewhere.

 

I don't know exactly what your supposed to have for you year in terms of PSI, on my 88 Truck TBI, I needed around 50 anything less than 44 and the truck had no pickup, would stumble when you floored it and so on.. If the filter is new, I would unhook the filter and put the hose in a bucket turn key on.. If you can find a t fitting to go in between the filter and the pump and try the key again.. Still not enough pressure? Then you pump is more than likely bad.. The best fix!?! Is not to cut the car up above the fuel sending unit and remove the pump. It would be to drop the exhaust, drop the tank, Take out the sending unit, put it in a bucket of water with a hose in the bucket. let the hose trickle enough to let the water run out of the bucket, next day take the sending unit to a radiator shop and have them measure the sending unit, you want them to weld a tube down to the exact length of the pump pickup, Now you will not have a pump in the tank, If you do this work your self, trial and error, you would want a 3/8 of an inch betweent the tank and the new welded pickup tube.. Cut the wires to the pump on the inside of the sending unit, cut the wires from the top of the sending unit and strip back or out of the loom back to the middle of the car or where you want to mount your external pump, the pump should be at the same level as the bottom of the tank, put a filter before the pump, wire in the pump from the wires stripped back from the tank, mount filter, pump, and reconnect everything.. You will never have to drop your tank again, unless your fuel guage sending unit goes bad.. If you ever burn up a fuel pump you can jack the car up, take it out have it rebuilt or install a new one.. Holley has a good universal in-line fuel pump.. Your Chiltons/Haynes manual should tell you what pressure range you should be in.. Buy the correct pump..

 

After the initial prime, the fuel pump will stop running. It does this because engine oil pressure must be present to close the fuel pump circuit. So if the engine is not running (no oil pressure), the fuel pump will not run. You can temporarily bypass part of the circuit to allow the fuel pump to continuously run with the igntion ON by jumping the fuel pump relay.

The procedure above is a good idea, but a bit unrealistic. As long as you go with a quality fuel pump, and don't let the tank run too far below 1/4 tank, a stock replacement will be fine. Keeping the fuel level above the 1/4 mark keeps the pump mostly submerged and promotes longer pump life due to the gasoline cooling the pump during operation.

 

The idea of not having to pull all the rear of the car apart to get the tank out is a cool idea,but I don't really wan to mod. the sending unit can you not install a inline pump with the old pump stil in place

 

Yes you can, but it's not recommended. You want the least amount of restriction possible on the suction side of the fuel pump as possible. Having an electric pump drawing through a dead pump is a bad idea - the pump will run hot and will be very short lived, and the fuel volume will be signifcantly decreased.

 

A bit unrealistic? Thats BS... I think you telling people not to run their car past 1/4 of a tank to be a bit unrealistic.. How about launching hard with 3/8 a tank? Bet that pump will be unsubmerged again.. This was a common problem with Chevrolets during this time.. Thus I corrected the problem and killed many birds with one stone.. I will NEVER have to drop my tank unless the sending unit goes bad.. I'm serious this is the best mod you can preform for the fuel..

 

some folks just dont want to hack their car up.. its not unrealistic, perhaps that was a bad choice of words. Its just not repairing to stock specs.. or its just not what most folks would do.

I personally would simply drop the rear and the tank, and replace the danged pump that way.

 

Yes, but for only a short time. Running for hours on a pump that isn't cooled because a lack of fuel and cavitation is MUCH worse.

Dropping the tank is not as bad as most make it out to be. And the work you performed IS additional unnecessary work in this case. Again, a quality stock replacement pump should last a long, long time.

I'm glad you're so proud of your work. Be sure to post up whenever that pump you recently installed fails, so we know for SURE that all that additional work was worth it

 

Thanks for all the input , i don't think any of the ideas were bad except my own about using a inline pump with the old unit still in place I think I will purchase a good quality pump and replace it as the factory unit was installed . any suggestion on a good pump for a stock305 that will be getting upgrades later. Oh ya my fuel gauge stays on full is the sending unit faulty or the gauge. thanks

 

If your fuel gauge stays on full that means there is an open in the sending unit circuit. The most likely cause is the wiper of the sending unit is not making good contact with the coil and probably needs to be replaced. If your lucky when you get it out you may be able to take it apart clean the contacts with some very fine sand paper but most likely it is shot.
The real bad news Chevy quoted me $600.00+ excluding the pump for the sending unit

 

I dropped my tank and but everything back in 2 hours. It's not as hard as everyone makes it out to be.