Engine/Transmission (1998.5 - 2002) Overboost and Rough Idle?

[vjohn346]

Hello fellow members,



I borrowed a OBDII scanner tool today and got the notorious over boost code. I've read alot of posts on the overboost and am not too worried about it. Since the engine is stock, I must need a new MAP sensor or I need to work on the wastegate I guess.



Here's what I'm wondering. Since I also have the bad idle when warm problem that I can't figure out, are these two possibly related? If you throw a over boost code, does the engine go into a limp mode that causes a rough idle. What about if the MAP sensor is giving faulty readings, will this cause rough idle?



One more thing. The idle is really rough but if I turn the engine off for a minute or two and restart, it idles great but the intake heater appears to be cycling and won't stop? Is this normal? The truck is still at operating temperature, so why is the heater cycling? I assume it's cycling because the voltmeter drops down for a few seconds and then returns.



Any help is again appreciated and sorry for all the questions but this idle thing is driving me bonkers:{ .



Thanks,

Vance

 

[LSMITH]

If the grid heater is cycling when the engine is warm I would pull the IAT sensor and check it out. You can put an OHM meter on it and check the resistive values against known values (do a search for the values).



I doubt that the idle is related to the code, but could be related to the IAT if it is in fact bad.

 

[vjohn346]

LSMITH,



Thanks for the reply. I put a new IAT sensor in about 2 weeks ago and it didn't seem to change anything.



I don't think the MAP and bad idle are related either but it's worth a try I guess.



Vance

 

[Turbo Trucker]

I had to replace the wastegate actuator on mine, it was leaking and causing overboost.

 

[SEmerson]

It will idle smooth in limp mode.

 

[1tuffram]

Vance,



What's the outside air temp when you notice the grid heaters cycling? Seems to me even if the engine is warm, if the outside air temp is below a certain temp it triggers the heaters. Both my '95 and '02 trucks do this when the weather turns cold. Do your grid heater continue to cycle even when you are driving? I think once you are traveling faster than 15 or 20 MPH the electronics deactivates the grid heater function and they should not be cycling.



Practical Solutions has a device to stop the problem of the grid heaters cycling when the engine is warm.

 

[vjohn346]

Turbo Trucker,



I'll check the wastegate and make sure the actuator is working. Should I be able to open the wastegate with a pair of pliers? I assume it's pretty tight since it holds 20lbs boost.



1tuffram,



The temperature outside was about 45 degrees. I had been driving the truck for about 30 minutes on the interstate and it was at operating temperature.



What is this Practical Solutions part, do they have a website I can go to?



Thanks guys,

Vance

 

[Turbo Trucker]

To check it you need an air compressor, or maybe you could rig a bike pump to work or something. Anyway you need to blow air into the wastegate actuator where the tube goes into it. It should move the rod. Don't give it more than 45 psi.

 

[csevers]

www.psdieselproducts.com

is the web site I have the heater saver and it works nice if the engine is warm the heaters don't cycle at all the way it should be, I think the guy you want to talk to is gordon.



Craig

 

[1tuffram]

Originally posted by vjohn346

Turbo Trucker,

1tuffram,



The temperature outside was about 45 degrees. I had been driving the truck for about 30 minutes on the interstate and it was at operating temperature.



Thanks guys,

Vance

My '95 service manual states: "If the intake manifold air temperature is 59 F or below, the air heater elements are energized". Further reading said during the Post-heat cycle (after engine is running) if an engine RPM of 32- 475 and intake manifold air temp below 59F the heaters will continue to cycle. Depending upon intake manifold air temp, engine RPM and the predetermined PCM values, one or both of the relays and one or both of the heating elements may be activated. Each element draws approx 95 amps at 12 volts. The post heat cycle will continue up to 3 1/2 minutes. I also found that if the vehicle speed is above 10 MPH the heater will stop cycling. I'm sure not much has changed for the grid heater system from '95 to your truck (maybe someone with a newer service manual for the 24v engine can verify this).



I have notice my grid heater will cycle even if engine is at operating temp and the outside temp is really cold. If the air is not being warmed above 59F by the engine heat before it reaches your sensor the heaters will start to cycle. I have also noticed on cold days when driving thru parking-lots the heaters will cycle for longer periods of time (observed by the volt meter needle), sometimes the needle will not even pop back up until I either let off the go-pedal or speed up above 10mph... and this is with an engine at operating temp (both '95 and '02 trucks).



What you are experiencing may be normal, I say may because you stated earlier the heater don't stop cycling and at only 45 F outside temp I'd be a little suspicious. On my '95 truck I only notice the above mentioned cycling at operating temp when outside temps are low 20's or less. Have not payed that close attention with the 2002 truck, but I know the 24v trucks have better (more efficient) intercollers, so it may be normal to see this type of heater cycling with higher outside temps.



Sorry for the long post, hope you find it helpful.

 

[vjohn346]

1tuffram,



Thanks for the heater grid information. It looks like my heaters are working properly according to your service manual information.



csevers,



I'll check out the website. The heater saver sounds like a good idea since I do alot of in town driving during these cold months.



Turbo Trucker,



Thanks for the wategate info, I'll give it a try this evening and see what I find.



Thanks again guys,

Vance

 

[csevers]

HEATER SAVER

I hate havin the heaters cycle ever time you start an already warm engine it is a waste of juice and hard on the alt and batterys before I got the heater saver I would let the truck run all the time when stoped now I can shut off for short trips to hardware store or such.



Craig