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  #1  
Old 05-06-2013, 12:44 AM
black87buick black87buick is offline
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Default Fuel pressure required.

Long and short, bought the car, previous owner spun rod bearings, I put her back together got her running so now working out bugs and fine tuning. Learning along the way. This is my first '87 GN car and first turbo charged gas engine with electronic fuel injection.

car has 60# injectors w/ matching chip according to documentation from previous owner.

I have set the IAC valve & TPS with the scan master procedures posted here. The car idles up and down from 1000 to 850 RPM. Found one vacuum leak that helped reduce the fluctuation frequency, but still idles up and down with the occasional drop to around 550rpm.

Fuel pressure is @ 40 lbs and stays relatively constant when idling.

I did searched the forum but haven't found anything yet. Maybe this is too obvious but please forgive my ignorance.

Now for the stupid question.

Does the idle fuel pressure need to equal the pressure spec the injectors are advertised?

60# injectors = 60 PSI @ idle ?

Sorry guys I really don't know this stuff. I do have an adjustable regulator that has been untouched since I put the engine back together, the car came with these injectors, regulator & chip installed.

btw Scan Master int = 128 upto 136 when idling. This is another reason why I am asking.

Thanks
-Chad
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1970 Buick Riviera
1987 Grand National
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  #2  
Old 05-06-2013, 03:40 AM
Shawn N's Avatar
Shawn N Shawn N is offline
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Default Re: Fuel pressure required.

The idle should be 850 to 950 rpm's so that's normal for it. If it's dropping down to the stall point then the culprit most likely is another vacuum leak or the IAC (Idle Air Control) is dirty but could be spark or fuel related. The fuel pressure is ok and don't go to 60psi! A little more info about what has been done the engine might help us out a little more and help with the process of elimination.
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Old 05-06-2013, 03:39 PM
black87buick black87buick is offline
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Default Re: Fuel pressure required.

-Heads, intake etc port polished and look great. EGR removed
-.030 over bore.
-CAM: TA_V264H
-Stock valve train (I did not do anything to the heads when I bought the car.)
-6162E Turbo
-Alcohol injection (not sure of brand)
-Scan master 2.0
-60# injectors.
-hotwire kit w/ fuel pump...pump unknown at this time but is in working condition.
-Turbotweak v5.6 Chip programmed to work with alcohol (non emission).
-3000rpm stall converter.

I cleaned the throttle body by removing it and also separated the IAC housing and cleaned it. I did the Scan Master IAC reset procedure. When it is in the 900 rpm range the TPS and IAC values are acceptable per the procedure.

I know there was at least one vacuum leak. It still has some brittle looking plastic lines. I will begin replacing all the hoses. So this may still be the cause and this would cause the 'int' value to go beyond 128 @ idle? Meaning a lean condition right?
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Garage:
1970 Buick Riviera
1987 Grand National

Last edited by black87buick; 05-06-2013 at 03:44 PM.
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Old 05-06-2013, 04:16 PM
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Default Re: Fuel pressure required.

Sounds like a vacuum leak (pretty bad one too).

Also, NO fuel pressure should not match the injector rating. The 60# injectors (assuming MotoTron/Seimens) are rated at 43 psi pressure across the injector (inlet to outlet). More pressure = more flow

Basically, the equation is:

NewFlow = {Square Root (P2/P1)} x RatedFlow

where:

RatedFlow = Original injector flow rate (lbs/hr)
NewFlow = Injector flow rate at modified pressure (lbs/hr)
P1 = Original fuel pressure set point (psi)
P2 = Adjusted fuel pressure set point (psi)

So, for example ... let's say your 60# injectors are running at 50 psi (no vacuum compensation).

They will then be acting like:

NewFlow = (sqrt(50/43) * 60)
Or
~66 lbs/hr

Knowing these injectors like I do ... they are actually much closer to 65# injectors @ 3 BAR (or 43.5 psi rated), so they are closer to 70# injectors at 50psi.
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Old 05-06-2013, 04:23 PM
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Default Re: Fuel pressure required.

INT aka short term fuel trim default is 128 on the scanmaster so it's normal. If it's adding fuel the number goes higher and the lower the number means it's subtracting fuel. I'm still thinking it's a vacuum leak somewhere in the engine system.
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Old 05-06-2013, 10:25 PM
black87buick black87buick is offline
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Default Re: Fuel pressure required.

Ken & Shawn,

Thanks for the help and thanks for the fuel equation! I will get rid of these plastic lines and use some rubber. It's comical how many breaks of plastic are joined with rubber.
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Garage:
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1987 Grand National
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  #7  
Old 05-08-2013, 10:27 PM
black87buick black87buick is offline
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Default Re: Fuel pressure required.

Ok, I removed all extraneous and suspicious vacuum hoses meaning I only plumbed what the diagram shown on the AC box nothing else.

I noticed that I am missing the check valve for the canister hose.

Issues that persist are:

Car starts hard when cold (not change prior to hose removal)
Car idles rougher (regression = idle worse)

Prior to hose removal and plumbing, I had sprayed engine cleaner on the intake, around the throttle body etc. No indication that there is a leak around the intake seal etc. I am thinking of trying the other chip I have that is marked "Turbo Tweak v5.6 60# inj, Alcohol emissions" chip.

What are your thoughts?

Thanks,
-Chad
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Garage:
1970 Buick Riviera
1987 Grand National
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  #8  
Old 05-08-2013, 11:56 PM
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Default Re: Fuel pressure required.

Time to start checking on fuel/spark if it's not vacuum related. Check the fuel filter and if it's been there awhile change it ($12). Most of us know good reliable mechanic's across the country so if it's driving you mad just let us know what city and state you are in and we will recommend one in your area if available.
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  #9  
Old 05-09-2013, 12:14 AM
black87buick black87buick is offline
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Default Re: Fuel pressure required.

Thanks Shawn.

The car isn't registered yet and I would like to continue to troubleshoot on my own. I'll start with the fuel filter, maybe try a different fuel pump. I am still scratching my head on why fuel pressure is still good. I had to clean up some of the fuel pump wiring in the tank...it was crazy. Maybe see if I can do a chip/injector swap with my buddy's '87 GN. I know the base ECM is good because we tested it in his car.

-Chad
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__________________
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-Chad

Garage:
1970 Buick Riviera
1987 Grand National
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  #10  
Old 05-09-2013, 12:17 PM
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Default Re: Fuel pressure required.

Check the EGR and see if it is carboned up and maybe hanging open a little bit. That is a pretty famous cold start symptom (and bad idle).

Also, swap MAFs with your buddy just for grins and see what happens? It may be a bad MAF (or poor reconditioned one).
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1987 GN original owner 650+ HP Black
2015 BMW 328xi XDrive wagon
2012 Volkswagen Tiguan (the Tig!) Night Blue Met (sold)
2006 Trailblazer SS Red Jewel Tint 395 HP AWD (sold)
2014 Silverado LTZ Crew 4WD
2012 Honda VFR 1200F Tahitian Blue (sold)
2015 BMW S1000R Racing Red
2013 Honda CBR500R Red (wife's bike)
2014 Triumph Bonneville T100
2003 Harley Davidson V Rod Anniversary Edition
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