That'll do it.

 

Per alloro -- At zero oil pressure you should have continuity to be able to turn on the idiot light, not an open. Also, I'm having difficulty in following the results you posted because you don't mention how your meter leads are hooked up.

I have got a few minutes here to answer this. I am not sure I follow your thought but here goes.

The oil sender/pressure switch( whatever it is called) is a 2 wire item with a 1/8 pipe thread fitting mounted on the rear of the engine on the passenger side of the distributor. It has a gray wire and a gray/yellow stripe wire. I disconnected the wires and probed the two maleterminals in the connector. Volt/ohm meter was set on about 20K?? ohms (don't remember this number for sure- I plan to retest this sender/switch some more and will be more precise). I simply pressured up the sender/swich and touched the probes to the terminals and held them in contact until the pressure bled from 60 to zero. That's how I determined the 60 -----> 10 -----> 2----> 0 psig readouts on the volt/ohm meter. If this does not explain what I did, let me know what else you might need to know.

By the way even at 0 pressure and no continuity, the idiot light still comes on.I know this for sure and is why I originally thought this sender/switch was bad.This is one of the reasons why I want to go back and check this item again. There might be another sender/switch for oil pressure or the idiot light. I want to be convinced before moving on.

Notice again what I said about tricking the computer for this sender/switch.

I'll be back later this evening.

Thanks, DB

 

Some senders use the body as terminal 3 (for the idiot light portion of the circuit) which is why I needed to know how you were testing the sender. What do you get for readings (if any) when you connect the ohmmeterfrom each of the terminals to say the threaded nipple part?

 

alloro LOL This is so funny. I have been out testing and guess what I was testing for --- Just exactly what you asked. Here's what I did.
I was thinking the same thing as you -- Maybe the body is the ground for both terminals and apparently it is. here is what I got --

A -- 0 pressure -- Terminal 1 to body ---- closed (continuity)
B -- 0 pressure -- Terminal2 to body ---- open (no continuity)

C -- 30 psig ------- Terminal 1 to body ---- open
D -- 30 psig ------- Terminal2 to body ----closed

I also bled the pressure off to see ifit switched at ~10 psig and it does.

All this would indicate the switch is ok.

I can not figure how the gauge works because I get no change in resistance as the pressure is bled off measuring from each terminal to ground and across the terminals. Looks to me like it has to change for the gauge reading to change. My readings indicate this is just a switch. It may have a piso-electric chip or something that varies voltage for the gauge reading-- I don't know.

I went back to checking from terminal to terminal on the sender unit itself and it is just as stated previously --- the circuit is open from terminal 1 to terminal 2 at 0 psig. The Chilton's manual says this would indicate a bad sender/switch unit --- I am not so sure.

Testing from terminal 1 to 2 is what my Chilton's manual recommends --- Note: My manual shows only 1 wire from the computer to the sender unit -- the gray one. The gray/yellow stripe is not shown in my manual's wiring diagram.

Also with the wire harness disconnected, neither the idiot light nor the gauge work.With wire harness connected, both idiot light and the gauge work. I tried cranking with the sender/switch disconnected and same old story --- run for 1-2 seconds and shutoff.

I don't remember if I said so or not but the engine is hard to start but it will fire after 5-10 seconds --- sometimes even within 1 second.

Basically, I am unsure if this thing is ok or not.I am leaning toward it is ok.I may just get a sender/switch unit and try it.

Thanks again for the help, [sm=thanx.gif]
DB

 

According to your readings the sender is good. Think of a relay with anormally open and a normally closed set of contacts. Terminal 1 is common, the body is NC and terminal 2 is NO. At zero pressure the path is terminal 1 to body - idiot light on. Above 2 psi the common (terminal 1) switches over to the NO (terminal 2). So now the circuit for the light (body ground)is broken and the path now goes to terminal 2 which feeds the gauge. Between terminal 1 & 2 is a variable resistor who's resistance falls asoil pressure increases, causing the gauge to climb. You might not be seeing this change in resistance between the terminals if your ohmmeter is set too low. If set too low and the resistance of the sender exceeds the ohmmeter scale, you will get continuity or infinity.

 

The one thing you have yet to do is a compression test. It's an important and still unknown variable at this point, so I think it's time.

 

September 23, 2007

alloro --- Compression testing

I had a chance today to check the compression with a screw in type tester and here is what I have found:

1- Did not check - Difficult to get to and had limited time.
2 -120 psig
3 - Did not check - Difficult to get to and had limited time.
4 - 95 psig
5 - 122 psig
6 - 125 psig

I know the 95 psi on No. 4 is low and rechecked several times to be sure and it definitely is low. Broken spring or bad valve seat maybe ?? The 120+ on the other cylinders seems on the low side but I don't know what this engine's compressionshould be. Please note that there was no indication of hard starting or skipping or rough idle and no smoke prior to this engine just quitting. The 95 psi on No. 4 could be causing a rough idle but I would think that is about all. Theengine should run on the other cylinders. When the engine does fire, it makes no unusual noise.

After compression testing I tried to start the engineand it ran rough for about 15-20 seconds then died. 5 or 6 attempts to start again and it was the same old run for 1-2 seconds and die.

I did notice the spark plus were very dark (almost black) but I discounted this as my attempts to start with the engine rich. I have run down the battery 5 or 6 times testing this thing.

stev

I checked the throttle position sensor again and it has no dead spot.
I am sure I cleaned the IAC completely.
Air mixture being blocked -- I just don't see how. The valves are the only obstacale. Air breather is off and butterfly opens.
There is a vacuum tube between the MAP sensor and throttle body. It is open. I checked it when I removed the MAP sensor to test.
http://wwww.dodgeram.org/tsb/1997/08-21-97.htmThis is a starter problem and not engine starting.
No security or theft system.
The battery cable was not pulled off while the engine was running prior to this no start condition. See original post.
Wire connections to the PCM look fine. I did unplug and replug also.
Tested the ASD relay relentlessly -- see above. Besides no spark or fuel injection if ASD is bad.
http://findarticles.com/p/articles/mi_qa3828/is_200105/ai_n8942314 I am familiar with this article.


Thinking of this next ---
There is a wiring harness which contains the CPS and CRK sensors and it runs right across the driver's side of the engine between the head and intake manifold. This would be a hot area and may have damaged the insulation. Problem is I am not getting any codes to indicate a problem with either if these sensors.

Maybea very bad vacuum leak ?? I have not considered it because usually if the engine starts, then it will run at moderate to high RPM even with the leak. I have not seem any disconnected vacuum hoses.

Any other thoughts guys ?? I will consider anything at this point.

Thanks again, [sm=dontgetit.gif]
DB

 

The bad news:
I hate to say it, but judging from those compression reading you have a mechanical problem andI think your timing chain jumped a tooth. Normal compression is 150 psi and there should never be more than a 25 psi difference from your lowest reading to your highest. The other possibility is worn rings or scratched cylinder walls. The only way to determine which problem you have is to squirt about a teaspoon of motor oil into one of the already checked cylinders and see if the compression rises significantly. If it does, it's a ring or cylinder wall issue. If it doesn't, it's the timing chain. Low compression will signal an overly rich exhaust in the O2 sensor. This will in turn cause the PCM to cut back on the fuel and stall the engine. The black plugs confirm and overly rich/unburnt fuel condition.

Now for the good news...everything I just wrote can possibly be throw out if :
1. The engine was cranking a little slow due to a run down battery, causing the low compression readings.
2. The plugs are too fouled to fire properly or are not the correct ones.

You could try a brand new set of plugs and give the battery a good overnight charge and see if your problem goes away.

 

TZ,

There is a little idle air slot under this IAC port on the TB. If this is clogged or blocked, the engine is a no run for idle. That's the reason for the penny check. Seeing the picture below, you are looking right at the IAC port. Just below the IAC port, inside the chamber area, is a little narrow air slot that allows the engine to run at idle while the butterfly valves are closed. The little idle air slot is just under the IAC hole on the inside and on the floor of this chamber. Make sure nothing is blocking this little slot.



I can't get a camera inside that chamber at all. You can feel that little idle air slot with your index finger too. If you do, you might push the crud out of the slot as well. When cleaning the IAC TB, I found this port with only 50% available air making it's way into it. After some thinking I had realized that the air flowing past the IAC mechanism had to go someplace. Well, it is this little slotted hole it passes to for a run start idle. Your engine is a Magnum series just like mine.

I cleaned that little IAC air slot with a swap and the same cleaning fluid in my How To Clean the IAC write-up.

 

alloro ---- Compression testing

I plan to go back and dig into these compression results more thoroughly. I am suspicious of these test results. The engine only has 60K miles and I change oil regularly. ( I have never seen the oil pressure less than 40 psi) I will also check all 6 cylinders. Does it not seem strange that cylinders 2, 5, and 6 all have worn at the same amount ?? (This fits with a possible jumped tooth though.) If I have to, I'll pull the valve cover and check the valves and springs on cylinder 4. I will try your oil in the cylinder test if I need to.

Jumped a tooth ?--- Yeah maybe --- I would think this more likely than cylinder/piston ring wear. If so, that means the intake valves are not completely closed before the compression stroke starts. I am not looking forward to pulling the timing chain cover. I think I am going to see if I can detect any leakage from the intake valves first. This engine has a metal timing chain and not a belt. I guess it could be it is not being properly oiled.

stev IAC

I know the opening you are talking about and it is open. I did pull the IAC motor off the throttle body and cleaned it and the openings. There was some build up but not what I would call excessive.

Ok guys, thanks for the thoughts again. I guess I have some work to do this week. I'll post some news when I have it.

Thanks, [sm=thanx.gif]
DB