Engine/Transmission (1998.5 - 2002) intermittent boost gauge problem, MAP sensor?

[johncameron]

For the past few weeks my boost gauge has been acting funny now and then. Sometimes the boost will become non responsive and hover around 5-7LBS at idle and slowly come back to 0. The truck is driving fine without any codes, could it be a map sensor failing? I've had to change 2 sensors in the last 2 months so that is what I'm leaning towards.



Any ideas for troubleshooting.



Thanks,



John

 

[CBeeman]

I wouldnt think an after market boost guage would have anything to do with your map sensor. If you dont have low power and everything else seems normal I would make sure your boost line isnt kinked or that your gauge isnt malfuntioning.

 

[NoSeeUm]

Is the Big Hoss where you are getting your boost indication? Because it likely uses the electrical signal from the OEM MAP sensor.



If so I would think you are on to it, but it could just likely be a wiring problem or the Big Hoss itself. I don't think the failure rate on MAP sensors is all that high.



If not and you are using a mechanical gauge then its are way off. At least for me it is impossible to get any boost at all on a pressure gauge when at idle. The turbo is just not spinning fast enough to put out much air. I bet the pressure is not more than a few inches of water.



How is your boost when you are working the engine?



Jim

 

[johncameron]

Yes I have the Big Hoss that takes it's boost reading from the map sensor, it also takes it's main power from that sensor. I am getting the proper boost (no more smoke) and the engine is not performing any different from normal, it is just the strange readings now and then.



It seems that when towing and this condition occurs, the boost will hover 2-5lbs higher than normal until I push the boost over 20lbs. When I do that the gauge becomes more responsive and reaks my normal peak boost of ~35lbs. When I let off it drops quickly as usual down to ~10lbs and takes a long time to get to 0.



The fueling seems normal even when this situation occurs, I was wondering if my SMARTY is omitting the boost readings and that is why I'm not having driveability issues?



thanks, John

 

[NoSeeUm]

I am not familiar with the Big Hoss. Does it tap the pump wire?



Not many people know exactly how the Smarty does it boost thing and I am not one of them. But I am certain that it does not mess with the signal from the MAP. It just changes the way the ECM deals with whatever MAP signal it is getting.



The Big Hoss on the other hand, will likely mess directly with the signal. How it works is like this. The BH connection should go first on the MAP sensor, then the OEM connection on top of that. The signal from the MAP is intercepted by the BH. Then the BH muddles with it and sends another signal to the ECM as to how it wants the ECM to react to that signal. Sending a signal of higher boost pressure might make the ECM think boost is high enough to fuel harder when it really isn't. The BH will also make sure that the ECM never sees a signal that would make the ECM think that boost is over 20 psi so that the ECM does not defuel on high boost. It could also send a signal of lower boost pressure and make the ECM defuel, but I am not sure in case of the BH.



At any rate, the boost you see indicated on the BH should be what is actually coming from the MAP. IMO it sounds like an electrical glitch of some sort and you might consider hooking up a mechanical gauge at least temporarily to use as a reference.



Jim

 

[johncameron]

Yes this big hoss only taps the pump wire and does no timing like the other model. (yes there are 2 different ones..... ) It is a great stack with the smarty because the BH only starts to fuel somewhere between 6-8LBS of boost. Thats how they keep their stuff "smokeless". The smarty takes care of the 0-8LBS lag:-laf .



If I were to unhook the BH completely, put the stock boost elbow back in and return to the stock SW will the ecm set a code if the map sensor is reading high boost? The only problem I see with that is I have DDII injectors so that would skew those readings. I'm having a hard time troubleshooting this problem. I really don't want to get rid of the Banks stuff as I like it, and I'd have to replace my boost-EGT gauge too#@$%! They both are hooked to the BH.



John