Puzzling fuel pressure drop – Buick 3800 V6

[GeekPriest]

I’ve got a 2002 Buick Regal with the 3800 V6, normally aspirated. I bought it with a slight hesitation, which turned into major power loss and eventually a tow.

Symptoms and overview:
1. Cranks and starts, but dies immediately.

2. Fuel pressure at the rail originally primed OK then dropped almost immediately to 0 (but see below).

3. Pump is new, based on early determination of a failure. I’m not 100% confident in my diagnosis here, so maybe that was a parts changer move. I did actually try to make the diagnosis, though. Nonetheless, there’s a new Delphi fuel pump and filter. When dead-heading the pump with a gauge on the supply line AT THE PUMP (so gauge only; no fuel flowing through the system), a 2 second prime shoots pressure to 80 psi, which takes about 5 minutes to drop to 60 psi, which then takes 15-20 minutes to drop to 55 psi. I think the check valve and pump look like they’re working just fine.

4. If I dead-head the fuel rail (capping the return so fuel can’t flow), the pressure holds steady and high (70+ psi) for several minutes. This led me to replace the fuel pressure regulator with a new Delphi one.

5. Fuel pressure at the rail NOW primes OK (50-55 psi; spec is 53-59), but drops quickly to around 10 psi before fading to 0. So the new regulator improved the situation, but didn’t solve it.

6. Visual inspection of the fuel injectors (lifting the fuel rail and pulling them free from their ports) confirms no leakage. This is in agreement with the finding in #4.

7. I don’t see or smell leaks along the accessible fuel lines.

8. The crankshaft position sensor signals look great on the scope. 18 even pulses and 3 pulses of different widths, all nice and lined up. I did not look at the camshaft sensor signal yet, and that could be relevant based on its connection to injector firing.

So questions:

Q1. Where the heck is my fuel pressure going? Why is it dropping at the rail? What needs to be looked at here.

Q2. What am I missing?

[GeekPriest]

I forgot the codes that were reported:

P0108 MAP Pressure circuit high
P0300 Generic misfire (misfire counts below)
P0404 EGR Circuit range
P0730 Incorrect gear ratio (transmission code)

Misfire counts reported, connected with the P0300
#1 2594
#2 586
#3 77
#4 46
#5 169
#6 142

[GeekPriest]

More updates.

I pulled the fuel pressure regulator (again) and made a special effort to clean the housing, especially where the o-rings seat. Lubricated the o-rings with gas, and seated the regulator, rotating it 180 degrees twice (back and forth) to ensure everything was seated. Then put the c-clip back.

The car now holds pressure at the rail of around 52 psi. It still doesn’t stay running, but it stays running about half a second longer than before. Progress.

[tedgtfan]

Have you checked the fuel pressure purge valve solenoid?

[tedgtfan]

Have you checked the fuel pressure purge valve solenoid? Also if you are scoping, you might want to do a current ramp of coils (I think it is terminal J on the connector) to make sure you not dropping out input to coils. Seen that, wires lay on radiator hose and dry rots insulation.

[jortegaa3289]

I’m constantly searching on the internet for posts that will help me. Too much is clearly to learn about this. I believe you created good quality items in Functions also. Keep working, congrats!

[1928nash]

Try relating the MAP (Manifold Absolute Pressure) to your problem

[Author]

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