Boost fuel cut?
 

I have searched but perhaps I am using the wrong keywords. I have just purchased a fd from a good friend who has too many on his hands(a dream). Whenever I boost my car above 7psi the car acts like it has a fuel cut and will not rev it just sputters and cuts out but keeps on when the gas is off. ANy idea what it might be? A vacuum leak? A ECU problem? Thanks for any help!

sounds like a vac leak. check your MAP sensor.

What rpm? what boost are you reaching
stock boost is 10-8-10
if you go over 12 ecu will cut fuel.

if it was the map sensor it would run like shit all the time, and it would still rev. you would have to keep your foot on the pedal to keep it running.

thanks for the input everyone! i just went outside to start the car to find out what was wrong and found out the starter bolt wiggled loose while I was driving it home. I had to put a starter in the car because the previous owner was troubleshooting one of his other fd's and tried this starter and never put it back on. ill let you know what the problem is when i find out what bolt i need. thanks again!

does anyone have a picture of the map sensor? i cant seem to find it...i cant find any vacuum leaks or anything either...thanks!

https://www.rx7club.com/attachment.p...hmentid=216328

The sensor has one vacuum line going into it, and a couple of wires. There is a sticker on it that says "boost sensor" or maybe "pressure sensor."

-s-

+1 for the pic

sounds like a vac leak which is making you boost over 11-12psi which is making the ECU cut off fuel.

could a exhaust leak cause any boost problems? i think it could but i dont know for sure. i have a hks downpipe but the gasket to the cat is ruined and leaks horribly but noone around here sells them. ive tested the map sensor and it is fine.

very easily possible.... exhaust leak = boost creep = ECU freaks out and cuts off

I think it would take a massive exhaust leak to do that. I'm talking ear against a vacuum cleaner loud exhaust leak.

Dave

It's probably the map sensor or a fuel pressure/pump issue.

an exhaust leak or boost leak won't cause fuel cut it reduces boost it doesn't increase it. It could however burn up your turbos hehe.

I've had an exhaust leak so bad the poor car only made 4 psi in 4th gear at red line.

The gasket on the wastegate door blew out.

i can get the car to kind of buck or lose power at higher rpms with less boost (1psi). i also found that i have no gasket between the hks downpipe and cat (aftermarket) that has a massive leak. im going to go get a new gasket soon but still cant figure out what is causing this problem. ive tested the map sensor and its good. maybe the tps is out of adjustment? i have replaced all the vacuum lines under the intake manifold also. any other ideas? thanks!

could it be a grounding issue?

did you try resetting the ecu that fixxed my bogging/bucking/backfireing prob

Alright I guess I should define my problem a bit more since I can't figure it out nor can any mechanic I've talked to. I am open to any suggestions on mechanics that work on rotary engines in the Raleigh, NC area too. My car idles great, starts perfectly, never floods, never stalls, and pretty much runs great other than one problem that may be more than one but I haven't figured it out yet.

I can be driving my car and whenever I happen to open up the throttle (pedal) and gain boost pressure the car will rev up fine and start to pull and just as it hits around 7 psi (varies depending on rpm and pedal input but generally between 4-7 psi) it will hesitate (bucking, jerking) and if I get on the gas hard at all it will backfire and loose all power but will be fine if I let off the gas. If I go back to hit the gas hard it will do the same thing and it is very consistent about when it happens and never fails to show its head.

I do not have any particular rpm range it fails at and I've been fumbled about this for awhile. I just bought this car two weeks ago but I haven't been able to see what it can do because every since I got the car it has had this problem. The previous owner has no idea what the problem is either. I had to pull the car around and put a starter on the car because it was off the car for one reason or another. After I put the starter on it started up but died because the coils had to be replaced and the previous owner told me so.

I replaced the coil and some vacuum lines and got it running fine. I put some new plugs in it and it drives great after a oil change. I can't figure out what the problem is but I have checked both the MAP sensor and the TPS. A friend said it could be the cat clogged but the exhaust flows great out the rear. Thanks for any help!

(I broke it up a bit for ease of reading!)

Swap out ecus and try that.

Sounds like it might be fuel flow. Have you tried replacing the filter yet?

Yeah, could be secondaries not switching in properly or the fuel pump not going to the higher voltage too.

This is pretty easy to check. Dale recently wrote a thread about upgrading the positive supply to the FP. You can tap into the wires at the FP (accessible under the carpet in the rear hatch area) and hook up a multimeter to them which you can view while driving. On my 94 touring FD, I found the voltage reading to be 9.x volts at idle or mild throttle settings. When I reved the engine it jumped to 12.x volts and would stay there as long as I was hitting the gas. I did Dale's upgrade and now get 13.x volts at the FP when it kicks into high.

If your pump isn't kicking into high, you will only ever see 9.x volts at the FP and this would act like fuel cut when fuel damand was high. I don't have the wiring diagram handy, but there is a high/low relay that the ECU triggers. Under low demand, by default a resistor bank is switched in to lower the voltage to the FP. When the ECU actuates this relay, the resistors are bypassed and the FP gets full voltage (almost). The almost part is what Dale's upgrade was about, to eliminate the resistance from the ignition switch so the FP does see nearly full battery voltage when it kicks into high.

Replace the fuel filter, if it hasn't been done recently.

-s-

Asked Scotty ^^^, but it turns out this is not his engine bay. I am trying identify the SMIC pictured in this shot. Also curious about the IC shroud, is that custom? Anybody?

https://www.rx7club.com/attachment.p...hmentid=216328

That's the Greddy SMIC with it's "duct".

Duct it is. So it comes with that, or is an option? Do you know about the pipes and elbow, are those all Greddy too?

yes and yes