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Old 04-09-2004, 11:32 AM
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Default Replacing distributor with an HEI in a MPI 4.0?

My CJ 85 with 258 block, 95 head, ported & polished with 2.02/1.75 SS valves, slightly shaved head and 95 MPI continues to have problems with pinging. As the CJ warms it becomes SEVERE.

I have done the following:
*GM MAP sensor and it is running rich. Fuel pressure is good.
*Plugs are a descent brown-tan color.
*Installed a 195F thermostat instead of the 180F in the original block/head.
*Adjusted the CPS appropriately.
*Dropped the heat range of plugs in all cylinders.


The mechanic who has modified/run many semi-stocks suggested that I consider replacing the distributor with a HEI, module from fireway, etc. He had suggested cutting the knob from the existing distributor in order to adjust it, but thought the use of HEI would give better options. I have not read a posting on this as a possibility.

Appreciate your thoughts on the replacement of the 95 distributor with the HEI, etc.?
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Old 04-09-2004, 03:36 PM
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Default Re: Replacing distributor with an HEI in a MPI 4.0

If this is a MOPAR MPI .....errr doesn't the distributor fire the injectors??? That is the cam position sensor is in the distributor. The crank position sensor triggers the coil.

That could be a 96 + thingie though...
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Old 04-09-2004, 05:08 PM
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Default Re: Replacing distributor with an HEI in a MPI 4.0

The MPI, computer, sensors, etc are from a 95 cherokee.

I haven't talk to the mechanic beyond what I posted above.
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Old 04-09-2004, 06:57 PM
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Default Re: Replacing distributor with an HEI in a MPI 4.0?

Before doing all that try checking the timing right now.
Make sure it DOES NOT ever exceed 35 degrees at any speed and at any load.
And - Try running without any vacuum to see if advance / ignition is the cause of the ping.
If it still pings, changing distributors - to any kind - won't help a bit - it's not the source.

The HEI will have a hotter spark, but probably a slightly different advance curve - depending on where you are getting the vacuum advance now. Hotter spark won't stop, or promote ping.
But the advantage of the HEI is you can get an adjustable advance diaphram for it.

You said it's running rich - it that by smell or with an infrared exhaust analyzer?
Smell you cannot tell rich or lean - either rich or lean you smell HC. Rich puts out excessive CO - colorless, odorless gas.
You could tell if you had clouds of black smoke - but that's visual.
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Old 04-13-2004, 07:27 PM
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Default Re: Replacing distributor with an HEI in a MPI 4.0?

Any one know of a mechanic in the West Central Minnesota area who has the solid, proven, expertise to work on the pinging issue in my CJ7. Hell, I might be willing to even haul it some distance to the right person.
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Old 04-14-2004, 06:53 AM
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Default Re: Replacing distributor with an HEI in a MPI 4.0?

Too bad you don't have the old renix system. A pinging sensor was part of that system. Some 4.0's have a high altitude CPS for a bit more advance. Check the advance on your rig. maybe you have a HA CPS and need a regular CPS.

You also mentioned a rich mixture. How do you know. A too rich mixture also causes pinging. The XJ electronics make an engine run rather lean, but with no problems. If mixture is a problem, try the adjustable MAP sensor as described on www.madxj.com . Why do you have a non-original XJ MAP sensor?

What compression ratio is your engine? If it's decked too much, it will ping, whatever you tinker. You might need a thicker gasket to bring CR down.

I don't know anyone to take your rig to.
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Old 04-14-2004, 07:08 AM
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Default Re: Replacing distributor with an HEI in a MPI 4.0?

I must add that the 4.0s distributor doesn't do anything regarding timing. It's a disstributor only timing is set in the computer. It uses the CPS as a TDC mark. Load (MAP), rpm (CPS), temp, O2, and throttle (TPS) are input on which the computer decides the timing and fuel amount. A HEI wouldn't make any difference. 4.0's are not notorious for cross firing or weak sparks. The HEI brings a CJ ignition on the strength of an original XJ ignition.

Your problem might be a wrong distributor. Do you run a 4.0 distributor? If not, yours is adding advance on the advance it allready gets from the computer. Twice the advance should cause some severe pinging!

I guess you used the entire electronics from an XJ or Wrangler with TB, computer, harness and O2 and (almost) everything. Where is your CPS? On the bellhousing or on the pully? What kind of dist you have? The original 4.0 has no advance mechanism in it.

Keep us informed.
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Old 04-14-2004, 03:39 PM
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Default Re: Replacing distributor with an HEI in a MPI 4.0?

**My distributor is from a 95 XJ. It does not have a vacuum advance.
**The CPS in on the front harmonic balancer with notches and sensor.
**The Chevy MAP sensor was supposed to be set rich when run on a Jeep motor.
**The deck was milled between .10 and .20. It did not ping before the electronic fuel injection.
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Old 04-15-2004, 04:53 AM
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Default Re: Replacing distributor with an HEI in a MPI 4.0?

OK.
I still wonder why there's a non-Jeep MAP sensor in this setup. Why a rich mixture? You have lambda system (O2 sensor). If the MAP signal (load) causes the computer to run a rich mixture, it probably also advances the timing, thus cause pinging.

I'd put a timing light on the balancer, after having checked if the TDC mark on the pully really is TDC. See if there's any difference in timing between the <nobr>Chevy</nobr> and <nobr>Jeep</nobr> MAP. If the Jeep MAP shows less advance and you still think you need to run richer than standard 4.0 setup, try ford injectors. This topic has been on MWB a lot, so plenty of info available.

If timing might be off, no matter what, you still have a problem because the CPS is non adjustable. This problem was a topic on this board a few weeks ago.

And to make sure: timing is not set by rotating the distributor in this setup, so leave the notch on. Advance is decided by the computer, fed by signals from various sensors. A HEI is no way a solution for your problem.

So:
- Check the TDC mark;
- Check the advance from the chevy sensor and a Jeep one.
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Old 04-15-2004, 06:28 AM
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Default Re: Replacing distributor with an HEI in a MPI 4.0?

</font><blockquote><font class="small">In reply to:</font><hr />
A HEI is no way a solution for your problem

[/ QUOTE ]

OK, I was too fast with that. A separately set up HEI enables you to decide the ignition advance. But you might be camouflaging a problem that is caused elsewere. You also interfere in a system that normally works great and has good reliability, power and economics. No idea if leaving the ignition out of the system affects the FI in another way.
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