4 replies to this topic

[Manuel B]

The guy that last worked on my '93 SPI told me he had pulled the spring in the fuel pressure regulator to make it longer and raise the pressure, it ran great before the crank angle sensor went sour, my question is what it the original length of the spring ?, does extending the spring have any positive/negative effects ?,

[spotmaxwoody]

Have you seen this spring, because im not sure there is one in the regulator???

[xrocketengineer]

You might need somebody to measure the spring for you. I looked in the Heritage Motor Centre parts list and neither the spring nor the regulator assembly show up.
The theory is that increased spring length (or stronger spring) will increase fuel pressure.
Your best bet would be to check the fuel pressure and see if it is ok. According to the HMC manual the pressure should be 1.0 Bar (14.5 psi) with the engine running and the pressure should not drop more than .7 Bar (10.2psi) in one minute after shutting down the engine. It also says that if either of the figures are not met, to replace the regulator unit which is a non existing part in the part list.
I have checked the fuel pressure successfully on GM cars with TBI using a cheap (less than $20) Harbor Freight gauge set. It should work even better on the Mini since the hose by the injector is the one disconnected by removing a clamp. The gauge set includes "T" fittings and even an extra piece of hose for the test. For a GM TBI car you have to purchase separately a threaded adapter that replaces the inline fuel filter to connect the gauge.

Ivan

Edited by xrocketengineer, 05 June 2011 - 12:25 AM.

[Manuel B]

Thanks for the info, I thought if I knew the correct spring length I would just compare them, if I check my pressure and it's not to specs I would still have to take the spring out and try and squish it down somehow, put it all back together and check the pressure again, this could take a few times to get it right, vs. knowing the correct length to begin with,
What would be the effects of my pressure being too high ?. any purpose to doing this ?, My top end speed is down a bit compared to before all the other problems started, on flat I could hit 100 easy and 105 was not hard, only for a quicky, but at Talladega I never got over 92, my bear hit 97 one day but it's not like it was before,

[xrocketengineer]

Maybe the bear knows how to use the "draft" better when passing.

As far as the pressure goes, my understanding is that you want to maintain the pressure at high rpm on high performance motors so you do not run lean. Under those conditions a standard system might be struggling trying to keep up and maintaining the pressure and fuel flow rate. However, I would assume that on a standard car, if the pressure is high (within reason), the engine would run rich during a cold start up. Once it is up to normal temperature the lambda sensor would provide feedback to control the mixture back to normal. If the pressure is ridiculously high, my guess would be that the car would get flooded and would not even run.
Maybe Sprocket can shed some more light on this.