questtuner82 Posted January 25, 2014 Report Share Posted January 25, 2014 ok so im trying to find out what the factory fuel cut psi is in full boost on a factory 87 quest tsi. im kinda worried of engine going boom because i feel that my car is overboosting drasticly. i have an aftermarket vac/boost gauge and in full boost im hitting 18psi and not hitting fuel cut. so can someone please tell me what the fuel cut is supposed to be at. Link to comment Share on other sites More sharing options...
kidjc Posted January 25, 2014 Report Share Posted January 25, 2014 Do you have any modifications? 88-89' is higher 12.8 I believe. The 87' was lower if not mistaken, around 10.8? I'm sure that several on here can give you the exact FSM info, try looking it up here, I'm sure it's there. IMHO, you're running high if you have no mods to support it. GL Link to comment Share on other sites More sharing options...
questtuner82 Posted January 25, 2014 Author Report Share Posted January 25, 2014 see thats what im trying to figure out. my car is all original except for the engine itself. i built the engine 2k ago and the motor has a basic rebuild except for forged pistons marnel njv head with+ 2 mm oversized valves and a 292 crower cam. everything else on the car is original computer wise. it does have a header and t3 flanged 70a/r turbo with 44mm wastegate and manual boost controller. but no other mods. but my car doesnt hit fuel cut at all and ive had it cranked to 20 psi full boost. i turned it down but it still has alot of boost compared to what i always read Link to comment Share on other sites More sharing options...
speedyquest Posted January 25, 2014 Report Share Posted January 25, 2014 After reading your post my first instinct is to ask do you have a wideband installed? What are your air / fuel ratios? Link to comment Share on other sites More sharing options...
scott87star Posted January 25, 2014 Report Share Posted January 25, 2014 I don't believe it has a fuel cut. John aka starquestrescue has done the most work in figuring out what the stock ECU is doing and has never mentioned a fuel cut. The FSM never speaks of it, at least not my 87 FSM. What feels like fuel cut to most guys is the MAF signal getting really noisy and confusing the ECU, I guess that's a cut. Link to comment Share on other sites More sharing options...
Speedy2222 Posted January 25, 2014 Report Share Posted January 25, 2014 knock box pulling timing is almost confused with fuel cut Link to comment Share on other sites More sharing options...
Dad Posted January 25, 2014 Report Share Posted January 25, 2014 You really need a wideband so you don't blow it. It will tell you whats going on so you don't blow it up Link to comment Share on other sites More sharing options...
questtuner82 Posted January 27, 2014 Author Report Share Posted January 27, 2014 i know i need to get a wideband put in the car. car isnt on the road legally yet so i dont get to really drive it like i should. ive put 31 miles on it in the last 2 years. but back to fuel cut...... im told by alot of people that every factory turbo car has a fuel cut built in which is a failsafe so u dont blow engines. its read from the map sensor. which reads the manifold absolute pressure. ive read somewhere of a person using a fuel cut defender on a starion on the boards here to get to the 25psi mark. and im told that our cars in 87 at least have a fuel cut of like 12psi. im just trying to figure it out and i dont need to have the motor go boom Link to comment Share on other sites More sharing options...
TainterRacing Posted January 27, 2014 Report Share Posted January 27, 2014 No real fuel cut.. you can max out the mass air tho .... Now getting a wide band is a very very good Idea. Link to comment Share on other sites More sharing options...
StarquestRescue Posted January 27, 2014 Report Share Posted January 27, 2014 On the 87-89 it is load based like the dsm's and 3000 gt's. There is no map sensor on the 87-89 or the dsm or 3000 gt. The ecu looks at air flow and a few other things to determin the engine load. The fuel map ends about 2000-21000 hz. That amount of air flow will max out the injectors. Below 4000-4500? the ecu may shut off the injectors breifly if it sees high air flow. At higher rpm it is more tolerant of being run at the edge. Mas over run is a big problem with the stock and 1g mas and produces a simalare "cut" experiance. This is much more dangerous as the fuel is not cut off clean, but is cut back based on the bogas air flow signal I ran into what looks to be a dsm style fuel cut running E85. I was adding about 25% fuel at wot and 30% at cruise on top of my gas settings. The air flow was above 2000hz for about .5 seconds prior to the injectors shutting off. http://i237.photobucket.com/albums/ff45/StarquestRescue/Data%20logs/E85fuelcut.jpg Link to comment Share on other sites More sharing options...
StarquestRescue Posted January 27, 2014 Report Share Posted January 27, 2014 Note the ragged airflow in this log screen shot. Then it trends down, even though the car was still accelerating . The car likely lean misfired causing the "cut". This crap blows motors. http://i237.photobucket.com/albums/ff45/StarquestRescue/Data%20logs/Fuelcutdifferentview1-1.jpg Link to comment Share on other sites More sharing options...
scott87star Posted January 28, 2014 Report Share Posted January 28, 2014 im told by alot of people that every factory turbo car has a fuel cut built in Ignorant people because they're just guessing, John has data and is thankfully sharing it. Link to comment Share on other sites More sharing options...
markhansenconquest Posted March 24, 2014 Report Share Posted March 24, 2014 Thanks john , Good to see real data ........ Link to comment Share on other sites More sharing options...
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