Fuel Pressure Test Results

[auto obsessive garage]

Hi Everyone, moved the thread from the intro section as it makes more sense to post in here.

Backstory:
1989 SHO sputtered and stalled after a car show and after completing 80 miles of driving. Car would crank and sputter but not start up again until hours later when it cooled.

Testing:
I immediately wanted to test the fuel pump and found that the car idles at 28 psi. I’ve attached videos of the other tests.

When disconnecting the vacuum line to the FPR, idle fuel pressure jumps to 35 and holds.

When giving it throttle, pressure rises to about 32psi but then drops to about 25 psi.

Does this all seem like a healthy fuel pump to you guys?

I’m also conducting a stress test to see the pump is overheating since the car stalled going up a large hill in stop and go traffic.




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[SHOdded]

The regulator would be my first suspect. How do the cam and crank sensors look? Any issues with the tach?

Might be injectors if they are leaking down
https://shoforum.com/index.php?threads/hard-start-solved-injectors.136911/

Another look
https://shoforum.com/index.php?threads/95-mtx-intermittantly-dies-in-hot-weather.123236/

 

[auto obsessive garage]

I'm going to check out the regulator next.

Cam sensor looks to be working, but I will test to confirm. Haven't gotten to crank sensor yet, but will look it over when doing TB and WP.

Car leaks no fluids (coolant, fuel, or oil).

Fuel Pump now whines louder during operation more so than when I purchased the vehicle. Are the fuel pumps loud on these? When the fans kick on, the pitch of the pump increases. I'm still leaning towards the fuel pump being on its way out...132k miles and 30 years would mean it had a decently long life, but I like to rule out everything before throwing parts at a problem.

It's only stalled the one time. Starts very easily. Idles great, drives great. I've let it idle up to operating temp and continued idling for 20 minutes with no issues.

 

[auto obsessive garage]

Also, thanks for the help. I really appreciate it. On limited/older/unique cars like this, information online can get a little cloudy. I've wrenched on quite a few rarer vehicles and it never surprises me how much of a variety of specs you find regarding pressures, torque specs, voltage readings, etc.

This forum has it together way more than most. Thanks again guys for entertaining my questions.

 

[luigisho]

If it's the original pump, that is way longer than any of mine lasted. The pumps seem a bit louder than most cars I've owned, but is it loud compared to other SHO pumps? I guess that depends on experience. Hard to put a finger on it over the internet.

 

[SHOdded]

If you want to replace the fuel pump
https://shosource.com/products?olsPage=products/walbro-fuel-pump-89-950

All fuel related components
https://shosource.com/products?olsPage=t/fuel-system

You don't NEED the 190, but I liked having it in there. 255 is overkill, and I am not sure on this, but may require a different regulator to go with?
https://shosource.com/products?olsPage=products/sho-nut-fuel-pressure-regulator-kit-89-95

 

[auto obsessive garage]

I’m going with an OEM style replacement. I have had good luck with Walbros in the past, but the 255 almost always requires an adjustable AFPR unless you’re upgrading the entire fuel delivery system.

Of course I have 15 gallons of fuel to syphon out first.


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[auto obsessive garage]

For anyone that’s dropped the tank...how difficult is it to reach the two hoses connected to the sending unit top with the plastic clips?

Assuming I will be doing this blind and on my back.


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[sperold]

Once the straps are off, the tank will come down enough to have access to any hoses or electrical connections.

My experience was the locking ring on the top of the tank is tough to get rotating (no spark implements and such). Everything else goes well.

If you want to cut the hole for future inspections, the tank removed situation is easy to accomplish at this point. I have never done it, but the case where it makes sense is, if you are nervous about a new pump early failure.

 

[auto obsessive garage]

Finally got around to swapping out the fuel sending unit. Went with cutting an access panel because to me it’s a value added mod.

So far no issues driving the car around and number look a little healthier too.


Key on engine off.



Idle (before was only 28psi).



Vacuum line disconnected (before was only 35 psi).

With that problem resolved...onto TB and WP, VC gaskets, changing all fluids, and a ton of other items.

So far I’m loving this machine. Appreciate all the help too guys!


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