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Fuel pressure question

 
Old 09-25-2010, 09:33 PM
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Hkp7
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Question Fuel pressure question

I have an 84 S US model which I had some trouble with for some time. The car suddenly started to run very rough with low power at around 20mph. I have changed a lot of items such as cap, rotor, wires, plugs, distributer, new air flow meter, both pressure regulators, pressure damper, both check valves near and on brake booster, all vacuum lines, tried injectors from a known good running vehicle, swapped jetronic and ignition computers from known good, replaced intake runner gaskets, boots, and throttle body o ring and boot. even put a new banjo bolt and seals for the trans shift module on the intake. I cant even think enough to list the rest but the engine appears new other than the fact it runs rough under load and has very little power. Question is pertaining to fuel pressure, I have 34 pounds of pressure at idle, when I increase rpm, it moves to 40 lbs and then quickly drops back to 34 even while keeping the same rpm. The vacuum I read from the port going to the fuel pressure damper is 17.5 inches. The book is telling me 2 bar for fuel pressure at idle which is 14.7 lbs per bar. Obviously something is wrong. Exhaust smells extremely rich as well as black soot on floor under it. Cat is hollow and O2 is new. With new regulators, good vacuum, same problem from before changing the regulators. Any Ideas.???
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Old 09-25-2010, 10:03 PM
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Could the vac advance hose have come loose from the back of the throttle body?
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Old 09-25-2010, 10:22 PM
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No, ive been diagnosing this all day, I was also thinking on a previous try out that I may have been losing vacuum through the valve in head to the purge valve, but purge is holding vacuum. I appreciate the responce. Also wondering on an 84, how does the injection computer know where the crank reference is?
I see no connection on the wiring diagram for the injection circuit.
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Old 09-25-2010, 10:24 PM
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Also, I am wondering if my rich smell is from being four pounds too much on fuel pressure. I wonder what the pressure does while under load.
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Old 09-25-2010, 10:28 PM
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How about the other end of the vac advance at the distrib ? No cracks, no splits?

G'luck.
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Old 09-25-2010, 10:36 PM
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other end holds vacuum and physically moves advance. I forgot to mention that all cylinders came to 150 psi on compression test.
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Old 09-25-2010, 10:43 PM
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Maybe Temp II sensor or Aux. Air valve not moving.

Search on those.

G'luck
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Old 09-25-2010, 10:49 PM
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any trace of fuel in the vac lines?
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Old 09-25-2010, 11:34 PM
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There is a green coax wire that leaves the distributer and runs to the passenger fender. The pickup is within the distributor. It is the reference sender on 84 USA.

Try disconnecting oxygen sensor wires.

Double check alignment of timing gears with notches.

Ensure distrib cap electrodes are polished clean.

Check for air box / filter clog.

A little more fuel pressure is insignificant

Bad grounds will cause this, too, and it can occur instantly, plus be intermittent.
The groundstrap will corrode beneath the plastic shroud, too.

Wondering about you coil, after checking above.
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Old 09-26-2010, 08:00 AM
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High vacuum at idle pulls the regulator pressure down - disconnect vacuum from regulator to verify. After that, the delivery is modified by changing injector pulse width, ie open time is increased as demand increases. The 40 and 34psi sound about right for L-jet.
jp 83 Euro S AT 52k
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Old 09-26-2010, 01:00 PM
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There is no fuel in vac lines, temp sensor 2 reads according to book, green wire is new, and has been checked, air filter is new, fuel is fresh, replaced all fuses on board, replaced fuel pump and jetronic relays, tried jumping fuel pump relay port and driving etc. All obvious has been gone over. I am considering maybe I overtorqued intake runners but I have sprayed them with carb cleaner with no change. I did a pulse test on all injectors and every one had an equal drop in fuel pressure. I am wondering if even though I have good compression, maybe something internal on engine?
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Old 09-26-2010, 02:06 PM
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As Landseer has mentioned I would check and verify the position of both cams to that of the crank at TDC, as well as verify the rotor on the distributor is in the correct position and pointing to the #1 plug on the distributor....if that proves out and the static and running timing is correct the next thing I would suspect would be the ignition system itself...coils can fail (partially) and give symptoms like you are having as can coil wires and the like. An inspection of the engine running in the dark might reveal arcing.....
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Old 09-26-2010, 02:18 PM
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I will check timing again, The wires are about four months old or so and have not changed them since the problem erupted. I am curious about what the coil wire is supposed to read. I am getting 1100k ohms. I did replace coil since problem as well. It was under warranty. The very last thing I did before problem occured, about a month prior, was change the fuel pump and fuel filter with new as pm. The last thing before that was changing the ignition switch with new from dealer. I appreciate all of your responses. Just funny when you check everything that would make sense and the problem is still there and its usually stupid and usually free such as a ground I found PO had in a place where no ground is present when my AAV was not closing.
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Old 09-26-2010, 05:52 PM
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Default Oil Pressure sending unit bubbling with engine off.

One thing that is concerning me is oil pressure. My gauge is maxed out any time the key is on so, I was checking the sending unit after driving car and I had oil bubbling from sending unit. It is making me think it is possible compression is leaking. Why would there be remaining pressure after engine is off. There is no oil in my coolant and no coolant in my oil. What would be the best and easiest way to check my oil pressure without the gauge on dash? I dont have an oil pressure gauge and I have no idea where I would hook one up.
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Old 09-26-2010, 07:51 PM
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The pressure senders are known to leak and fail as it appears yours may be doing....the leak is the clue. A new or known good sender is needed to get the leak resolved no matter what.....I would expect it may solve the pegged condition too....
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