SHO Shop blower - fuel issues?

[bobreimer]

I have an 89 SHO with a 9lb supercharger kit from the SHO Shop. Put the car on a dyno the other day and it builds power smoothly to about 280 hp at 5,800 rpm.

After that the power drops sharply. By 6,700 rpm it makes 138 hp. The belt is not slipping. The boost builds smoothly to 8.5 lbs at 6,700 rpm ..... but .... the air fuel ratio starts to go lean at 5,900 rpm and gets steadily worse as the boost increases after that.

The engine seems fuel starved. I have a new 250 lph fuel pump and 47 lb injectors. I suspect the fuel pressure is dropping off and I need to get a gauge on it to confirm this. I'm wondering if the original fuel pressure regulator isn't maintaining pressure?

Has any one else with a blown SHO had a similar problem?

Bob

 

[NotSoSlowSHO]

I'm wondering if the original fuel pressure regulator isn't maintaining pressure?

YOU said it

Get a gauge on that thing pronto. And you need an aftermarket FPR with the 250.

Also, what are you using to tune this beast?

 

[SHOMurph]

do you have the 255 hiflow or the normal 255?

Probably more than anything its your programming.

 

[AutoSHO]

The engine seems fuel starved. I have a new 250 lph fuel pump and 47 lb injectors. I suspect the fuel pressure is dropping off and I need to get a gauge on it to confirm this. I'm wondering if the original fuel pressure regulator isn't maintaining pressure?

Has any one else with a blown SHO had a similar problem?

Bob

Have you changed your fuel filter yet?

I would recommend going with one of SHO Nut's FPR kits if you find fuel pressure to be dropping off. It will allow the car to idle better as well as not running into lean fuel trims.

If you reset the computer does it change anything?

 

[bobreimer]

its a Holley 255 lph for forced induction cars ..... so i assume its hi flow?

 

[sho_sc]

Have you changed your fuel filter yet?

You wouldn't believe the problems I had because of a fuel filter.

 

[SHOMurph]

its a Holley 255 lph for forced induction cars ..... so i assume its hi flow?

hmmm don't know. I would check the flow rates for the Walbro hiflo 255 vs. your holley.

You shouldn't but you might need a boost a pump.

 

[yamahaSHO]

Holly and Walbro pumps are one in the same. I would test your fuel pressure and see what you get. I also highly recommend going with an adjustable fuel pressure regulator like Chris mentioned.

 

[sho_sc]

Can you post the dyno sheet?

 

[Lupo]

the air fuel ratio starts to go lean at 5,900 rpm and gets steadily worse as the boost increases after that.

Bob

You are going to torch a hole in one of your pistons if you are not careful.

How is your motor tuned, with an LPM? Is this the "complete" kit from the SHO Shop with LPM, and injectors?

 

[SHO Dude]

I suspect the fuel pressure is dropping off and I need to get a gauge on it to confirm this. I'm wondering if the original fuel pressure regulator isn't maintaining pressure?

Bob

The FPR would not cause a FP drop off. They don't work like that.

It could be the pump, it could be the tuning. A gauge will tell you quickly.

My money is on the tuning.

Which MAF?

 

[yamahaSHO]

An overpowered stock regulator does cause a fuel pressure drop off. With a stock regulator and a 255lph pump, Terry (twr), Will (FAST4DR), and myself found that the fuel pressure without vacuum is lower than with vacuum, considerably. I believe Will even has a video hosted and posted on this forum.

I'm not sure how the stock regulator performs with boost applied, but I suggest swapping in an adjustable regulator anyway. It's hard to tune when you don't have the fuel pressures you need when you need them.

 

[Patrick Norris]

An overpowered stock regulator does cause a fuel pressure drop off. With a stock regulator and a 255lph pump, Terry (twr), Will (FAST4DR), and myself found that the fuel pressure without vacuum is lower than with vacuum, considerably. I believe Will even has a video hosted and posted on this forum.

I'm not sure how the stock regulator performs with boost applied, but I suggest swapping in an adjustable regulator anyway. It's hard to tune when you don't have the fuel pressures you need when you need them.

I forget which end the sho fpr is on but most stock fpr apply vacuum to the fpr to restrict the return causing an increase in the rail pressure. So if you are running a larger pump you would more then likely push the pressure past the stock unit.

 

[RStalveyARFF]

that's the problem, the regulator can't handle the flow, causing overrun. The regulator is the last stop on the rails before returning to the tank and it's a classic case of trying to fight a fire with a 1500GPM pump but using a garden hose... the fluid just has no place to go.

 

[bobreimer]

You are going to torch a hole in one of your pistons if you are not careful.

How is your motor tuned, with an LPM? Is this the "complete" kit from the SHO Shop with LPM, and injectors?

Its the SHO Shop kit ....... came with an LPM, injectors etc.

 

[yamahaSHO]

The SHO Shop LPM and injectors are not the best choice. I would HIGHLY suggest selling the LPM and buying a TwEECer RT and tuning yourself. When I purchased my kit, I just bought the piping, bracket, hardware, hoses, and oil feed line and fittings. From there, I pieced everything together myself. My reason for doing that is I know what SHO Shop does and I knew it would cost me more money in the long run to outright buy the full kit.

 

[FAST4DR]

With the stock FPR and a 255lph pump the car will run lean in the higher rpms. That stock FPR causes all kinds of havoc with that much fuel flow.

Stock the car is supposed to have around 30psi idling. As the revs increase the manifold pressure decreases and the FPR opens allowing more fuel flow. The pressure is supposed to rise to around 40 psi. Ok, all fine and dandy.

Now, throw in over twice the flow and what happens is that the hole that the fuel flows through in the FPR is so small that the FPR is overwelmed and cannot return the fuel as fast as it's coming. So the fuel pressure INCREASES at idle because the orifice in the FPR is closed down. Mine was seeing 44 psi at idle! BUT, when the revs go up the FPR opens and allows more fuel flow and it must be enough to relieve the return problem and the pressure DROPS because of the now larger hole.

So what happens is the 02 sensors see a rich mixture at idle and back the fuel injector pulse width down for the 44psi pressure, BUT then as the revs rise the car is running lean, because the computer is expecting a consistant rise if fuel pressure, but actually the fuel pressure drops leaning out the mixture. Another problem is stalling as the revs come down. The mixture goes rich again at idle and bogs the motor down.

Get rid of the stock FPR. www.shonutperformance.com

Will

 

[SHOMurph]

With the stock FPR and a 255lph pump the car will run lean in the higher rpms. That stock FPR causes all kinds of havoc with that much fuel flow.

Stock the car is supposed to have around 30psi idling. As the revs increase the manifold pressure decreases and the FPR opens allowing more fuel flow. The pressure is supposed to rise to around 40 psi. Ok, all fine and dandy.

Now, throw in over twice the flow and what happens is that the hole that the fuel flows through in the FPR is so small that the FPR is overwelmed and cannot return the fuel as fast as it's coming. So the fuel pressure INCREASES at idle because the orifice in the FPR is closed down. Mine was seeing 44 psi at idle! BUT, when the revs go up the FPR opens and allows more fuel flow and it must be enough to relieve the return problem and the pressure DROPS because of the now larger hole.

So what happens is the 02 sensors see a rich mixture at idle and back the fuel injector pulse width down for the 44psi pressure, BUT then as the revs rise the car is running lean, because the computer is expecting a consistant rise if fuel pressure, but actually the fuel pressure drops leaning out the mixture. Another problem is stalling as the revs come down. The mixture goes rich again at idle and bogs the motor down.

Get rid of the stock FPR. www.shonutperformance.com

Will

With my hiflow 255 and the stock FPR I ran super rich all the time across the rpm band.

My programming was dumping in wayyy to much fuel.

Best to get the Josh's FPR but understand that it still might be your programming.

 

[yamahaSHO]

Let me guess, the WOT Fuel Multiplier was set REALLY low?