I have a problem with the car fuel cutting only when the ECU goes to closed loop. When in open loop I have no problem whatsoever, but as soon as closed loop is realized cut comes around 5 psi or sooner. I have a stock ECU 1200 injectors, freeflowing exhaust (3"no cats) streetported engine, non sequential mod< boost controller 10psi, The car will run in open loop fine even to 15 psi, but falls on its *** when it warms up and assumes closed loop. Any ideas?

 

Are you saying that you are running all of those mods, including the injectors, with the stock ecu? Have you ever read this forum or done any research?

I don't know how you haven't blown your motor yet, but it will happen....get an ecu for @%@! sake!

BTW, the car does not stay in closed loop under boost, only when idling or cruising.

 

Yeah, that doesn't make any sense...I don't think its possible to be running closed loop at 5 psi!

jds

 

What would cause fuel cut when the car warms up? If it is even fuel cut at all. Which sensors actually tell the computer to go into defensive mode? The car runs great , until it starts to sputter when boosted and warm. I have changed plugs, and run 30% toulene to up the octane value just in case. I dont drive the car very often, because of the large street port and the fact that the car is only fun at WOT not a user friendly daily driver. I am just trying to pin the cause of this problem. Does the knock sensor come into affect under boost,, and how about the O2 sensor, does the ECU read this under boost? It is an engine temp related deal and it runs good when the coolant temp is 150 or below, but it doesnt idle as smooth as when it warms up.

 

Why the hell won't you spend $450 on a used Pettit Unlimited ecu? Seriously.

 

If I can definatively pin the problem on the ECU then i will spend the money, but the car runs fine when it is cold , so it leads me to believe the problem is not really the ECU especially after you say the car is in open loop during boost. The ECU treats the 1200s as if they were 850s, giving them the same duty cycle, although they are introducing more fuel. Does the ECU fire the secondary injectors when the car is cold and under boost? or does it just fire the primaries when cold. Like I said I would spend the money, although if it doesnt cure the problem then it wont be well spent. What does the Pettit ECU do that the stock one doesnt?

 

I take it back re: the Pettit. Just get a Power FC. I forgot about the injectors.

A couple of comments:

1) the stock ecu cannot handle boost above 10 psi. It will fuel cut above 10.7 psi (in higher rpms). When you say you are hitting 15 psi, it must be for a very short period or somehow the ecu is not enacting fuel cut.

2) the stock ecu cannot handle the timing changes necessary for a street-ported engine.

3) the stock ecu cannot handle larger injectors. Not only is there the issue of a shitload of fuel getting dumped when it's not necessary, there are lag times for the larger injectors involved.

4) the car restricts output when it's in warm-up mode by not opening the secondary throttle butterflies. You should not be boosting high when in warm-up mode.

5) as a member of this forum, why would you even try to run all these mods on the stock ecu? Even without researching, you should have seen enough posts to know better.

6) Seriously, get a Power FC. Today. I really don't understand how you haven't blown your motor.

 

It doesnt have secondary butterflies they are removed. I agree a power FC is probably the right thing to do, but I dont understand why the damn thing runs so well when cold. I have limited the boost to 10 PSI for the time being, but have run the car through 4th gear at 16 PSI without a hiccup, when it was cold. What is the resale value of a power FC, after a year or so? If I keep the car i probably wont need the power FC, and can sell it.

 

I assume you're not getting any error codes?

The knock sensor is not likely to be doing anything. Supposedly the stock ECU will retard timing a bit if it sees excessive knock, but it is pretty widely accepted that this feature is of marginal usefulness in the stock ECU. The O2 sensor is definitely not read under boost. Its not read at idle either...this doesn't sound like your problem. You've got some variables there that the stock ECU is not built for, but again, I doubt that your problem is that, given that you have bad idle when the car is warm but not when cool. Some things to check, based on personal experience: air pump, if you still have it, temperature sensors (there are several...intake air, fuel, I think one other one) and of course, depending on its age, your engine wiring harness. I recently had major problems with the car NOT entering closed loop ever, running rich and fouling plugs, smoking, backfiring and just generally running like crap. No error codes. We finally decided to replace the wiring harness and pray. One of those two things did the job.

jds

 

What timing changes are necessitated by a street port? I've been running Pettit's standard streetport rebuild for a while, and while I usually use a Pettit ECU, when I first got it I used a stock ECU, and lately I've gone back to it temporarily since the Pettit stopped controlling AC a while ago. Then again, I've heard that the standard Pettit street port is about as mild as you can get and still call it that, so maybe that's why it still works well.

jds

 

No error codes and the car has 60K on it. The engine astually idles bad when cold, but good when warm. I am wondering if the secondary injectors even fire when the engine is cold, but if I were boosting just on the primaries it probably wouldnt run very well either. I was going for the fact that the 1200s would not let the car run lean and would richen the car up with the modified engine and flowing exhaust. If the car is running too rich does it stumble as well?

 

The car can definitely stumble if its running overly rich. Mine would do that ever time I'd take off from a standstill.

jds

 

Yea it ust falls on its ***, and backfires through the exhaust when coolant temp goes above 150 or so, and runs great when coolant temp is cold. I would do the power fc if I thought it would work, and I could get most of my money back out of it in 8 or 9 months. Ported rotaries arent extremely friendly to drive around town anyway, but I like the WOT runs.

 

The resale value for the Power FC is high. I'm not sure why you wouldn't want to keep it, but if you bought one and decided to sell it you should have no problem getting most of your money back.

 

I guess I DON'T think a new ECU would necessarily solve your problem...it sounds like something is simply not working properly, and it might be a bitch to diagnose (e.g. wiring harness). However, I do think you should get a PFC or some such for completely different reasons (e.g. not blowing your motor once you do get it running right).