Engine/Transmission (1994 - 1998) "cliking" sound, lights dim.....

[PGaither]

On my 96 Ram CTD. , I hear a "clicking sound" from under the hood, like a relay or something, and if my lights are on at night, they dim for 30-40 seconds, then I hear the "click" again, the lights get brighter again for 30-40 seconds, and then I hear annother "click" and they dim again for 30-40 seconds..... this repeats and goes on, and on... ... it either happens all the time (but not really noticed during the day, unless A/C is on), or definately whenever the A/C ,defoger, or floor heat is on. What is the cause of this? Is it some kind of relay? Where is it & how can I fix it?

 

[illflem]

It sounds like your grid heater is cycling on possibly due to a bad intake temp sensor or it's wiring.

Does it only happen under 17 mph?



Since this is engine related I'm moving this to 12 valve

 

[PGaither]

Thanks illflem, I have noticed it only when the truck is sitting in park, Idling. I'll have to check it at speed... ... what does it mean if it happens above 17 mph? The grid heater seems to be working fine, is that sensor hard to replace? expensive? How can I check it?

 

[Howard Durand]

PGaither,



My service manual for the 94 CTD states that the "Intake Manifold Air Temperature Sensor" is located on top of the intake manifold and to the rear of the intake manifold air heater.

It also states that the sensor is a variable, thermistor type sensor which inserts a variable resistance between PCM pin 21 and ground allowing the PCM to control the relays that activate each of the grid heaters which should not come on with manifold temperatures at or above 59 degrees F.

Below 59 degrees, the grid heaters are cycled on and off for varying lengths of time depending on the temperature.



The sensor has two wires. One goes to the PCM and the other is grounded to the engine.

The wire to the PCM is black with a red tracer and the grounded wire is black with a light blue tracer.



The manual says to test the resistance of the sensor with a digital volt-ohmmeter connected across the sensor terminals.

The reading should be less than 1340 ohms with the engine warm. (about 180 degrees F. )

At 32 degrees F. the resistance should read between 29,000 and 36,000 ohms.



Before doing anything, make sure the wires are properly connected at the sensor and that the terminals are clean and dry.

If the connector is loose or making bad contact the PCM could think it is 40 degrees below zero.

If you would like a copy of the pages from the manual. , PM me your e-mail address.

 

[Deezul1]

Over 17mph the grid heaters arnt needed and the PCM shuts them off

 

[PGaither]

Thanks for the help & advice guys..... I drove the truck last night to test it, heres what happened: The clicking noise, and lights diming every 30-40 seconds did indeed happen at startup & while idleing, then it keep happenning as I drove under 17-20 mph, as I went over 17-20 mph, it stoped (as you guys suspected), I drove about 3 miles/10 min. . , and it wasen't happenning annymore, even when I slowed down under 17 mph! I kept driving really slow (under 17 mph), and let it Idle in my driveway for a few minutes, and it wasent clicking & dimimming the lights annymore! weird... . my temp guage was reading about 150.....

My questions are, is it the grid heater relay (s)? Are there 1, or 2 relays? How do I test it (I do have a volt/amp meter), do I test the relay(S), or the wires that go in to the relay? I would assume the grid heater relay, right? Do I put the red probe from my meter where the black wire with red stripe went, and the black probe/lead to where the black wire with blue stripe went? I'm not very good at solving/testing electrical probelms, any help would be greatly appreciated (with as much detail as possible please). How much does the relay(s) cost, and where can I get one if indeed I do need one?

 

[PGaither]

Oh, and what am I looking for on the volt meter? (I am checking voltage, not amperage right?)... ... ... .

 

[Tomscreek]

It sounds to me like it's working exactly like it should.

 

[Howard Durand]

PGaither,



It sounds to me like your truck is doing just what is is supposed to do.

In the intake air heating system, there are two heating elements and each one has its own relay.

When manifold temperature is below 59 degrees F, they will each be cycled on for a certain period of time determined by the temperature. When one turns off the other turns on. (that is the clicking that you hear)

This goes on until operating manifold temperature is reached.



The heating elements each draw a considerable amount of current. That is the reason you see the dimming of lights and the voltmeter in the dash fluctuating.



There is obviously nothing wrong with the heaters or the relays in your truck.



There is a chart in the manual that lists what the resistance of the sensor should be for each temperature over a range of minus 40 degrees F to 248 degrees F.

For example:

At 0 degrees F, you should have a resistance of between 29,330 and 35,990 ohms.

At 50 degrees F, you should have between 17,990 and 21,810 ohms.

At 104 degrees F, you should have between 4,900 and 5,750 ohms.

At 212 degrees F, you should have between 640 and 720 ohms.



If you want to check the sensor with your ohmmeter, unplug the connector and place the meter leads on each of the pins in the sensor. It shouldn't make any difference how the leads are connected.

If you really want to check the sensor, I believe you could remove it from the truck, immerse the tip in water and with the ohmmeter connected, watch the change in resistance as you increase the water temperature. When it boils (212 degrees F) you should see the resistance between 640 and 720 ohms.



If you want to check voltage on the wire coming from the PCM, connect the red meter lead to the black and red wire and the black meter lead to either the black and light blue wire or directly to ground.



Hope some of this helps.

 

[illflem]

Don't have a manual in front of me but doesn't it also say the maximum time the grids will cycle after start up is 3 minutes?

 

[PGaither]

Thanks for all the help everybody... ... . sounds like it might be working right? (illflem, I'll check to see it it does cycle longer than 3 minutes, would that mean the sensor was bad?), and I'll check it with the ohmmeter after thanksgiving (it would be o. k to drive if the sensor was bad right? worse case it would stop cycleing after I reach 17 mph right?) Thanks again, and happy thanksgiving to everyone!

 

[illflem]

If it runs for longer than 3 minutes I would think the problem is in the PCM.

Personally I think all is normal with your truck, drive it and enjoy!

 

[Howard Durand]

Bill,



I can't find any mention of a definite time that they will be allowed to cycle.

My interpretation is that after the engine is started they will continue to cycle until intake air has reached the cutoff temperature.

If that is true I would think that a defective or disconnected sensor could allow them to cycle until the ignition switch is turned off or the cutoff vehicle speed has been reached.

 

[JJW_ND]

Failing Grid Heater Solinoid???

Unhook one of the two heavy wires that feed the grid heaters on the intake manifold. Secure so it can not ground. If this has no effect reinstall this one and disconnect the other. If this solves the clicking boucing volt gauge, one of the two solinoids that feed the grid heaters is failing. If this is infact the problem, it will occur at any speed and any engine tempurture. The volt guage moves up and down very fast and it is easiest to see at night as the lights to flicker.



Pretty cheap and easy fix. The solinoids are sold as a set.



jjw

ND

 

[illflem]

I'll try and bring my manual home but I have an intake temp gauge in my cab. In the Montana winter there's times it's cold enough that the intake temp never gets above freezing no matter how long you drive, never had the grids cycle except for a short time after starting.

 

[Howard Durand]

Bill,

I agree with what you are saying about intake temperature not getting warm enough to turn off the heaters.

Actually, the intake air only needs to be heated long enough for reliable combustion.

But I still can't find a mention in the book stating a definite time that the heaters will cycle after the engine is running.



The Haynes manual states that the manifold temperature must be less than 59 degrees F and the engine speed above 475 rpm for the PCM to allow continued air heating during the Post Heat Cycle.

It also says that the PCM contains a shut-off device that will discontinue power to the air heating elements if the engine stalls, the starter is engaged during Pre Heat Cycle, if the starter is operated for more than 10 seconds or if the vehicle speed exceeds 10 mph during the Post Heat Cycle.



One of the problems with the Service Manual is that there are bits and pieces of information about a given component scattered throughout the book and none of them will tell you the whole story.

 

[illflem]

OK, here's what my '95 factory service manual (page 14-92) says verbatim;



After the pre-heat cycle is completed, the PCM must receive an engine crank signal (engine speed between 32 and 475 rpm) followed by an engine run signal (rpm above 475) Intake temperature must also be below 59°F. All of these signals must be seen by the PCM before initiating the post-heat cycle.



The post-heat cycle will continue for up to 3-1/2 minutes unless the PCM determines one of the following features interrupts the cycle strategy.



*the engine starter is operated during the pre-heat cycle.



*the engine stalls during the post-heat cycle.



*the engine starter is operated for more than 10 seconds during the post-heat cycle.



*the vehicle speed is above 10 mph during the post-heat cycle.

 

[Howard Durand]

That is a much better description of the process than anything I can find in my 94 manual.

It seems almost everything I look up in it has some discrepancies.

I am glad they built the truck better than they wrote the manual.

Most of the information you show is included in the Haynes manual except for the 3. 5 minute time out.