Engine/Transmission (1998.5 - 2002) Cant figure it out?

[Alan Reagan]

Dang, Marco. Forgot about that. However, at idle, at sea level, it should be reading 14. 7, not 18.

 

[CstlEng]

14. 7 + 3 = 17. 7 or about 18psi at idle so that could be OK... but... . I thought that the newer 2nd gen trucks used absolute pressure and the older 2nd gen trucks used gauge pressure. Mine (a 99) shows . 50 volts map output at idle (piercing the output lead of the MAP with a digital multimeter). the newer trucks show about 1. 00 Volt as I understand it (and this is closer to what I see under acceleration in my truck when all is AOK). Or am I completely wrong and should shut up?

 

[Alan Reagan]

CstlEng, He shouldn't be getting 3 psi at idle. That seems a little high. My digital gauge shows 0 psi at idle. At sea level, then my absolute is 14. 7 at idle. My use of three pounds above is just showing that is all it would take to get to the point where the wastegate would open and the ECM would show a MAP fault if the 21 PSI is reached and exceeded.

 

[JyRO]

Eshaw -

while driving down the road just tap your brake with your left foot while keeping on the throttle it should duplicate the symptom on command.

Eshaw, are you suggesting that an otherwise great running truck (no codes & not exhibiting this problem) would do this? I'm not saying you're wrong, but it doesn't seem logical. Because your procedure (with a lot of throttle), is how some guys like to, "smoke brake. " That is, make a whole lot of smoke, by keeping the engine rpm down where its not getting enough air to stop smoking. None of those guys have mentioned going into limp mode. I've done it (although not much smoke), and didn't go into limp mode.



Maybe I don't understand what you meant?



- JyRO

 

[CstlEng]

Ah,Yes. Alan, you are right. I was thinking limp mode and writing idle. 3 psi at idle is too high. 3 or 3. 5 PSI is the max you would see in limp mode.



The real question is still "why is his truck going into limp intermittently. " I would say that we have now ruled out the MAP sensor as 2 different ones (an old and brand new) are exhibiting exactly the same performance. Does the BD box have somethhing that modifys the boost signal before sending it to the ECM to force the signal to be within allowable limits? The box I use does and it is a seperate component which could stay in the truck even if the box was pulled from the truck (in the first post jnelson states that prob exists w/ & w/o box, even if box in't in truck). That part malfunctioning could cause an elevated MAP signal to the ECM.



Are you sure you are seeing 18PSI at idle? If so have a look at the voltage out of the MAP and see what it is right there, and on the other side of the "signal conditioner" (if there is one). If it is right around . 5 V (or 1. 0V on a newer truck) and steady at idle on both sides of the conditioner and still showing 18 psi from the ECM, the problem would lie elsewhere for sure.



I don't think it would be an ECM/ sensor calibration issue as that sensor would calibrate at startup, and if it were an offset far enough off to mess things up once, it would keep messing up untill restart each and every time you had enough boost to overboost (every hard acceleration, for example). Idling wouldn't fix it. If you are not seeing 18PSI at idle and are seeing something like 14. 7 or 0 and the raw sensor signal voltage is behaving properly, I think the MAP angle is dead and we have to start looking in another direction. Please point out mistakes in my reasoning or other places I am incorrect.



How do you measure your LP fuel pressure? Electric sender? damped (glycerine filled) mechanical gauge? Would you pick it up if the LP pump quit for say half a second? Just trying to figure this out with you.

 

[Alan Reagan]

CstlEng made some good points. Somehow I losted situational awareness and had to backtrack to figure out what we were trying to accomplish. Following CstlEng's question is something I have pointed out several times on this board. One of the most common failures of the various boxes causes a MAP over/undervoltage error to be set in the ECM. An extreme error condition will cause the truck to go into the limp mode. The newer boxes do in fact intercept and alter the MAP signal on the CAN bus to negate the overboost code.

 

[JBrookshire]

What are you doing with your truck??

jnelson,

Just nosey, but what are you doing to put that many miles on your truck in that short of time???And glad to see the hi odometer reading on thet 24 valve

 

[DEZLPWR]

Re: What are you doing with your truck??

Originally posted by JBrookshire

jnelson,

Just nosey, but what are you doing to put that many miles on your truck in that short of time???And glad to see the hi odometer reading on thet 24 valve

Me too! You must be a hot shotter... .

 

[GeneralMachine]

MAP

I Agree with the post, here in west Tex the press set's @ 27, while the truck im refering to was at the stealer, the tech had DC on the phone they said the was showing 22psi with the engine off and that that was wrong. This is what they said they performed to fix the problem, a cal of the ecm, he said it should read 0 while engine stopped. I have not check this first hand, what i can say is the problem is fixed. this truck was worrying us bad it would be running fine the you would look to see if someone turned off the key, and would do this at all time's. Ill be glad when this one's fixed. I like this TDR



Harv

 

[jnelson]

Coming home yesterday as I rounded the corner, got down to about 30 mph in 3rd. As as started to accelerate I notced the rpm bumps UP not down as it hesitates. It may bump up 150-200 rpm. As I mash the gas and raise the rpm it quits.



When I was having really bas hesitation problems I replaced the APPS and it solved that problem.



I rarely give the engine an opprtunity to do this as I keep engine rpm above 1500 as much as possible while driving or towing.



Yes I do Hot Shot. I am leased to LoneStar Transportation and have my own bussiness CattaHay Transport.

 

[EB]

About 1yr. ago I sold my 95 3500 with 416,000+ miles on it. My "new" 3500 will roll over 98,000 tomorrow on the way to Larado, Tx. 90% of the miles on my new one have been with a 7,000 lb (empty wt. ) trailer behind it. Usual loaded wts. will run around 20k. The new truck has been very trouble free. Power steering leak, and non-working limited slip unit, (fixed under warranty) Other than that, nothing.

Old truck was an auto, put in two trannys, second was a DTT, that solved that problem. The only thing done to the engine was a power upgrade (plate in the pump) and the valves were adjusted a couple of times. The only reason I sold it was the front suspension was gone and the power steering and vacuum pump were shot, plus I need 6 tires, all that at once and I decided to get a new one. A guy had been trying to buy it from me for a year, so I sold it and got the new one. I still see the old one on the road taking vegetables from the Rio Grande Valley to Houston. It probably has well over 500,000 miles on it now.

There are a number of Dodge trucks in this area with between 400 and 700,000 miles on them. They are all hotshot trucks.

Sorry about the long post.