EGR & Oil pressure

89 Cherokee, Command-trac, 4.0, 154k
Hi guys. Some of you might remember my rough running post. Well, that's taken care off. A couple vacuum lines were bad and the air cleaners heat valve was stuck pointed to the radiator. Do I need that for emissions?

Anyway, two big things. The EGR doesn't open. The manual said the solenoid is supposed to allow vacuum to it if I unplug the solenoid, and it doesn't open the valve at all. I can pull the pintle with my hand and engine will roughen, So i assume the EGR's fine. Computer or the solenoid itself? It has vacuum to it.

The oil pressure gauge is almost always pegged WAY past 80. I looked for a broken wire and I did find one that was chafed, and I fixed that but no difference. It's worked for about 20 miles out of the 1000 I've put on since I've had it. When I unplug it, it stays pegged. When it is working, and the engines off, it doesn't read zero. It reads a touch under 10 then goes up to 30ish with a hot idle. What's up with this?

I really wouldn't mind just letting the EGR be, but we have emissions testing here in Massachusetts. Plus I dunno if it's pinging from not having it functional, since I have no clue what a ping sounds like.

They`ed nail you on the EGR here with Cali smog checks so I imagine that will show up the same there, plus you probably need to have it fixed anyhow. The O/P , have you tried a sender? I cant recall if mine is on 0 when its not running or not. Personally i never put much faith in jeep or Chrysler electronics and particulary guage accuracy. Rumor even in the Diesel trucks it not even a actual pressure reading, its soem kind of hypathetical calc the computer comes up with. Nuthin like real mechanical guages for piece of mind. BYW the O/P in my 87 is different every day it seems, even on the same longer trip it reads 40 or 55 or 37 all within 50 miles at the same speed and gear.I also posted a while back regarding temp guage diffs, every later 4.0 Ive had ran right at 210. Ive shot with and infared temp gun every where on the engine, head front and rear, mani,block,thermo housing,temp unit and its identical to the reads I get on my 87 which reads at about 170 on the guage, both run 195 thermos. My point was a 210 read on the 87 would actually be what,nuclear meltdown?

The oil pressure senders are notorious for going bad and telling lies......first get an external oil pressure gauge and compare the numbers to the one in the jeep.....if they are not the same replace the sender.

That heat riser in your air cleaner is there to aid the engine to warm up faster in the winter time(another little device I had no use for so I deleted it).Has no affect when the engine is warm.....helps out in the gas mileage department by warming your jeep up quicker.I don't see it causing you to fail an E-check....

About the egr....I got fed up dealing with mine and blocked it off.Not telling you to do the same but its one of those stupid emissions devices that drives people nuts(I know your plight...thats why I blocked mine off)

Some say they have passed E-checks without an egr valve.......But I've also heard of the smog nazis actually looking for it to verify that its there and hooked up.....you decide,depends on how strict your state is I guess.

If they do a tailpipe check at idle, you'll prolly pass with the EGR there but not functioning as it doesn't open at idle, but if they use a dyno to simulate driving conditions, you'd quite probably fail as the valve should open to cool the combustion chamber and reduce Oxides of Nitrogen IIRC-- haven't had to deal with smog checks in about ten years.:rof:I'm sure someone will correct me if I got that wrong

--Shorty

Plus I dunno if it's pinging from not having it functional,
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Yes it can. When you add in to the mix to much timing, poor gas octane, carbine combustion chambers wrong plugs, very hot air temps. Often it's a mix of more then one thing. Fix the EGR and clean of the carbine with a can of SF right down the TB.
If it still pings and you can and have set the timing up over stock. Back it off by 2 deg at a time until ping goes away.
Also often a ping will show up under testing (the jeep being pushed hard) But many people just do not drive that hard in DDing. If this is the case just let it ping a little the extra timing may get you a 1/2 MPG. luck
If your NOs are two high? backing the timing down to stock can help.

I was thinking it was the sending unit too, but if I disconnect the wire to the unit, the gauge's reading doesn't change at all. It stays pegged way past 80. Shouldn't it drop to zero because of the loss of voltage?

89CherokeePioneer said:

I was thinking it was the sending unit too, but if I disconnect the wire to the unit, the gauge's reading doesn't change at all. It stays pegged way past 80. Shouldn't it drop to zero because of the loss of voltage?

Click to expand...

Try grounding the oil pressure sender wire itself, engine on, you should get zero, or near zero on the gauge (in your case about 10 psi*). That tests the gauge and wire. Sounds like your OP gauge needs calibrating back to zero since it reads near *10 psi with the power off.

The Renix (87-90) OP gauge reads zero when grounded and over 80 when it is an open circuit. As the oil pressure rises the electrical resistance of the OP sensor increases. I think the newer Jeeps OP sensor works in the opposite direction. The Renix OP sensors sees max voltage and no current when the sensor wire is disconnected, and near zero volts and some maximum current when the oil pressure is low and the sensor is at maximum electrical conductivity. You should be able to test the Renix OP sensor with an ohm meter with the engine on and off to see if its resistance is chaging at all (just disconnect the gauge wire, then connect one ohm meter test probe to the sensor post and the other probe to the engine ground). I have not seen anyone post the resistance of a new OP sensor, but if you buy one you might want to test it and post the data for the good one and bad one here for future reference. It sounds like your OP sensor is bad.

On the EGR, check for voltage to the EGR solenoid, or connect 12 volts directly to the solenoid to test the solenoid itself. If the solenoid does not operate when you power it up directly from a 12 volt battery then it needs to be replaced. I forget if the solenoid is elctrically closed or NC at idle. I do know the EGR is NC at idle.