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post #1 of (permalink) Old 11-08-2002, 12:18 PM Thread Starter
 
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Adj fuel pressure reg. advice

Ok, so after searching and reading through many posts on the Mopar MPI system installed on a 258, I ran across many posts where people mention having an Adjustable Fuel Pressure Regulator.

My 86 CJ has a stock 258 with the Mopar MPI installed. I'm experiencing pinging at low rpms, high rpms, and especially on hot days.

The following post 83 CJ carb to FI conversion (contimplating) led me to a great web-site " Sierra Mopar Installation" detailing the installation of the MPI, and states that installing an Adjustable Fuel Pressure Regulator should cure my pinging problem.

Can anyone tell me if this has worked for them before I spend my cash on one? They seem pretty pricy for what they are.

Thanks!
Derek
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post #2 of (permalink) Old 11-08-2002, 02:06 PM
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Re: Adj fuel pressure reg. advice

I got mine from NAPA, it was about $30.
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post #3 of (permalink) Old 11-08-2002, 03:03 PM Thread Starter
 
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Re: Adj fuel pressure reg. advice

Really Jeepn?? The Hesco ones are over $200.00 for a CJ. Any idea what the difference would be? Did you find any performance difference after you installed it?
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post #4 of (permalink) Old 11-08-2002, 03:26 PM
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Re: Adj fuel pressure reg. advice

Maybe the ones for FI are different, mine is for a carb. It's adjustable from 0-10 psi and I usually run it at 2.5 or so to avoid overloading the carb. It's common and lots of people have bought the same thing.
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post #5 of (permalink) Old 11-08-2002, 03:31 PM Thread Starter
 
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Re: Adj fuel pressure reg. advice

Ahh! Thanks!
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post #6 of (permalink) Old 11-08-2002, 05:31 PM
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Re: Adj fuel pressure reg. advice

Just one thought.. On a SMPI why doesn't the SMPI fuel regulator do it's job? It seems there's too much return line pressure. [img]images/graemlins/confused.gif[/img]

On most SMPI"s I've never heard of a consistant cure for pinging, or for whistling from the Throttle body. [img]images/graemlins/frown.gif[/img]
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post #7 of (permalink) Old 11-08-2002, 06:15 PM
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Re: Adj fuel pressure reg. advice

Before you put out the money, you might try a trick I've read about. You can squeeze the stock regulator in a vice (pushing the inlet/outlet toward each other) slightly to increase the regulator's pressure. It may take a few tries.

I have the adj. regulator and it makes a difference, but it may not cure your entire problem. I have a stroker that has gone through various stages of pinging. When you crank up the pressure it will have an affect, but during start-up (before it goes into closed loop) it will run really rich. The tricky thing can be that oxy sensor will try to compensate for it.

The other thing to try (I would try first) is the adj. MAP sensor. I did a little write up of the one I made for $3.50 so it is low risk. I will attach it. So, after you have it installed, you can increase the voltage to MAP which will, in turn, increase the voltage out to the computer. Most people believe that you have to go to 5.3 vdc to see any results, but mine ran too rich at that level so I'm running it at like 5.17vdc.

I'm assuming you swapped head to the 4.0 head?? The 258 head is notorious for the pinging problems. If you don't know much about it, check Jaffer's 4.0 head page at www.monsterslayer.com/Jeep
Attached Files
File Type: doc 940105-MAP Sensor Write Up.doc (35.5 KB, 15 views)
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post #8 of (permalink) Old 11-08-2002, 06:58 PM
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Re: Adj fuel pressure reg. advice

Mostly I've seen the adjustable fuel pressure on MPI used to fool the system for other than stock displacement or injectors and to get the last few thousandths in the quarter.

Make sure you know what you are buying. Many people pedal an adjustable fuel pressure regulator for my TPI. You don't get a regulator at all, you get a new cap with a screw in it. I an making my own by pounding the top of the cap flat and brazing a half nut to the outside and putting a screw with a nut on the end through it. Pretty much the same thing they sell.
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post #9 of (permalink) Old 11-08-2002, 10:54 PM
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Re: Adj fuel pressure reg. advice

Are you absolutely positive it's a fuel problem?

Yes, way too rich can lead to detonation and carbon deposits
- they glow and pre-ignite the mixture.
Too lean can do it too - fuel is a coolant, lean runs so hot
it pre-ignites.

But - if your timing advance is not doing what the engine
requires, lighting the spark way too early "pings" too.

Check to make sure it starts at about the right intial point,
about 8 at idle, and advances slowly and evenly throughout
the RPM increase to about 3000 RPM. At that speed the
advance should be no more than 35 degrees tops.

A popular screw-up is to use manifold vacuum instead of ported
vacuum for the advance circuit.

If you have an advance problem and get the mixture off by
fiddling, all you accomplish is make it worse.

Easy to check it, and costs $0.
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post #10 of (permalink) Old 11-09-2002, 10:02 AM
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Re: Adj fuel pressure reg. advice

The advance is controlled through the computer based on inputs it gets from the Crank Position Sensor, the MAP sensor, the speed sensor, and the oxy sensor. You really have no way of changing the computer's tables unless you do one of the following:

* You can have the overall timing retarded up to 4 or 6 degrees with a DRBII type scanner/device. That's as much as the computer is programable.

* You can play with the crank position sensor and trick the computer as to what TDC is. The distributer has a sensor that works in conjunction with the CPS so it's not the best way, but it will get rid of pinging (and performance to an extent)

* Go to a completely custom computer like the desert buggy guys are doing. It's really expensive and you have to know what you are doing.

* You can play with the MAP sensor and Adj fuel pressure and larger injectors all to get different outputs from the stock computer, but sometimes it introduces too many variables.
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