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Stock fuel pressure?

54K views 17 replies 3 participants last post by  n0dih 
#1 ·
What does GM spec the fuel pressure for a 98 Monte Carlo Z34 L36 and for a 2000 Park Ave Ultra L67?

They use the same fuel press regulator, so I am assuming they should be the same.

Would like what GM says in the manual. Look up P0171 fault, should be showing in there where to go to find it.

Thanks!!
 
#2 ·
97 - 2000 VIN 1 & K KOEO 48-55 psi
97 - 2000 VIN 1 & K KOER 3-10 psi less than above

2001 - 2004 VIN 1 & K KOEO 53-59 psi
2001 - 2004 VIN 1 & K KOER 3-10 psi less than above

2005 VIN 1 KOEO 53-59 psi & 3-10 psi less running
2005 VIN K KOEO 48-54 psi & 3-10 psi less running

2006 3800 56-62 psi (Returnless System NO PSI drop when running)

2004 Pontiac Northstar VIN Y KOEO 41-47 psi & 3-10 psi less running

95 to 99 Northstar KOEO 48-55 psi & 3-10 psi less running (Return System)
2000 to 2005 FWD Northstar KOEO 41-47 psi & 3-10 psi less running (Return System)
2006 FWD Northstar 55-61 psi (Returnless System NO PSI drop when running)



Note: returnless system

  • The fuel pressure regulator attaches to the fuel module assembly. The fuel pressure regulator is a diaphragm-operated relief valve. A software bias compensates the injector on-time because the fuel pressure regulator is not referenced to manifold vacuum. The injector pulse width varies with the signal from the manifold absolute pressure (MAP) sensor. The fuel pressure regulator is a serviceable part.
 
#3 · (Edited)
I am puzzled....

Ok, the fuel press reg on a 98 Monte Carlo is PN 217-3294 or 217-1422. The fuel press reg on a 2005 Park Ave Ultra is 217-3294 or 217-1422. Autozone has a GP/Sorenson FPR PN 800-302 listed for the 2000 PAU and 2005 PAU. This is the PN reg we picked u. The stock OEM reg was a Bosch and it specifically said 3.5 bar on it.

But yet they have different rated fuel pressures. So looked at a 98 MC 3800 yesterday and fuel pressure was at 40 psi KOER and 50 psi KOEO. So being the parts book said they had the same reg on the PAU and MC Z34, figured the reg was bad. So we replaced and got KOER 42 psi and KOEO 52 psi.

But yet the spec is diff between the 2. How?

Is it really a bad reg out of the box? It is barely spec for the 98, but out of spec for the 05.

97 - 2000 VIN 1 & K KOEO 48-55 psi
97 - 2000 VIN 1 & K KOER 3-10 psi less than above

2001 - 2004 VIN 1 & K KOEO 53-59 psi
2001 - 2004 VIN 1 & K KOER 3-10 psi less than above

2005 VIN 1 KOEO 53-59 psi & 3-10 psi less running
2005 VIN K KOEO 48-54 psi & 3-10 psi less running

2006 3800 56-62 psi (Returnless System NO PSI drop when running)

2004 Pontiac Northstar VIN Y KOEO 41-47 psi & 3-10 psi less running

95 to 99 Northstar KOEO 48-55 psi & 3-10 psi less running (Return System)
2000 to 2005 FWD Northstar KOEO 41-47 psi & 3-10 psi less running (Return System)
2006 FWD Northstar 55-61 psi (Returnless System NO PSI drop when running)



Note: returnless system
  • The fuel pressure regulator attaches to the fuel module assembly. The fuel pressure regulator is a diaphragm-operated relief valve. A software bias compensates the injector on-time because the fuel pressure regulator is not referenced to manifold vacuum. The injector pulse width varies with the signal from the manifold absolute pressure (MAP) sensor. The fuel pressure regulator is a serviceable part.
 
#4 · (Edited)
Lets do the math
Running 38 psi is good. This will not set a lean DTC
Running 45 psi is good and won't set a rich DTC
41 psi is in the middle so wee will use that number.

To set a Lean DTC you will need to be adding about 40 percent extra mass of fuel per given mass of air to achieve set Stoich at 41 psi fuel pressure

The PCM s maximum authority to control long term fuel trim allows a range between +16 percent per fuel trim cell
The PCM s maximum authority to control short term fuel trim allows a range between +20 percent per fuel trim cell

VIN K

• Idle, purge commanded (Cell 10).

• Deceleration, purge commanded (Cell 1).

• Normal driving, purge commanded (Cell 2).

• Normal driving, no purge commanded (Cell 6).

• Idle, no purge commanded (Cell 9).

VIN 1

• Idle, purge commanded (Cell 10).

• Normal driving, purge commanded (Cell 2).

• High flow driving, purge commanded (cell 4).

• Normal driving, no purge commanded (Cell 6).

• Idle, no purge commanded (Cell 9).
 
#7 ·
The PCM s maximum authority to control long term fuel trim allows a range between +16 percent per fuel trim cell
The PCM s maximum authority to control short term fuel trim allows a range between +20 percent per fuel trim cell
I had the wrong number in for a lean condition. I corrected it now
 
#5 ·
4 cylinders have this DTC. you should ask John if he can add this or if it is in the calibration at all
DTC P1171 Fuel System Lean During Acceleration
The powertrain control module (PCM) can identify if the vehicle fuel system is capable of supplying adequate amounts of fuel during heavy acceleration. This condition is called a power enrichment mode of operation. If power enrichment is requested during a Closed Loop operation, the PCM will provide more fuel to the engine. Under these conditions, the PCM should detect a rich condition. If the PCM does not detect a rich exhaust at this time, DTC P1171 will set. A plugged fuel filter, or a restricted fuel line can prevent adequate amounts of fuel from being supplied during the power enrichment mode.
 
#6 ·
I'll check on the P1171.

With stock fuel injector flow settings this car is lean, LTFT's railed at +16.4% (they won't go higher than that for some reason, they peg there), and STFT's are in the +3-5% average. They get to 0 now and then, but rarely. Nothing is obvious at all, since this problem started, intake (upper/lower) has been replaced, another set of injectors put in (and swapped back, didn't fix issue), FPR changed, now we find by the book should be ok, swapped PCM to a 99 PCM (seemed interchangeable according to Hollander, works fine with full flash and CASE learn).

So according to the guy who cleaned the injectors he spec'd them at 20.95 @ 55 psi. Spec is 22 lb/hr @ ?? (assume stock pressure, is that KOER or KOEO?), so the injectors could be right, but could be 3 lb/hr wrong too. So if it is 20.95 @ 55 psi, then at 42 it is only 18.3074 lb/hr.

Which wouldn't 18.3074 lb/hr injectors in a 22 lb/hr application expect to cause a P0171?

I changed the injector flow to 19.6 to get the trims down, but they still don't seem right, they are dead on 0 LTFT / 0 STFT at times, then -7% LTFT, and sometimes +4 LTFT. But overall, much better than before, but still not where I would call it fixed.
 
#8 ·
I would say 85% of the time it is a MAF related issue.
A CAI is a MAF related issue
 
#9 ·
This car has stock MAF, stock air box with only a K&N in it. Nothing out of the ordinary. I was thinking same thing.
 
#10 ·
What is NORMAL or typical MAF reading at idle (closed throttle)?

What is NORMAL or typical MAF reading at idle (closed throttle)?
 
#11 ·
What is NORMAL or typical MAF reading at idle (closed throttle)?

That is a very good and important question.

The old rule of thumb was
8.xx gm/sec for 8 cyl
6.xx gm/sec for 6 cyl
4 to 5 gm/sec for 4 cyl

but that isn't the case. If a 6.0L is idling at 4 to 5 gm/sec it has an intake leak or a bad MAF. It should be between 6 and 8.5 gm/sec.

Leaving the Caddy dealer and going to the Chevy dealer I got my hand back on 3800 almost daily. I look at MAF readings on almost every car as a diagnostic tool. I have found that a given 3800 could idle about 5.5 gm/sec and the next (a different year) may idle at 4.2 gm/sec and both have good fuel trims.

I had a 96 3800 s/c with a stalling issue. It had a cracked vacuum line. The car would idle down to 2.9 g/sec when hot in park, AC off and only at times. The cell under it was 0 g/sec. If it hit the lower hz the car would stall. If I remember correctly when I was all done the MAF reading was 3.5 gm/sec and I felt that it was very low, but the fuel trims were ok.
 
#13 ·
Wow the Grand Prix vs the Monte/Lumina MAF xfer are way different
 
#14 ·
Yup, found the stock file.... Are they that diff under the hood (airbox and all?)
 
#15 ·
I didn't have time to pull the file for that vin, but I looked at a Monte SS and a Lumina and they were the same. Then I pulled up a Grand Prix and found it was different.
 
#16 ·
Subzero posted it on dax
 
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