Engine cuts out at high RPM, under power, and only after running
03-05-16, 08:48 PM
#1
Full Member
Thread Starter
Join Date: Jul 2007
Location: Tokyo
Posts: 181
Likes: 0
Received 0 Likes
on
0 Posts
Engine cuts out at high RPM, under power, and only after running
Okay, I've generally called my 7 Christine, due to the fact I'm pretty sure she's possessed by the devil, but I'm thinking of renaming her Clarkson, due to the fact she seems to be allergic to hard work now.
To begin with, I did search the forums using keywords like "sudden," "power," "loss," "dies," "WOT," "engine," and the such, and wasn't able to find a solution that I already tried.
The patient:
1985 GSL-SE, completely stock.
The symptoms are:
-Engine will only rev to 4500 after warmed up
-When trying to accelerate, engine just nopes out, and says "I feel like idling."
-Will maintain RPM and even accelerate a little when going downhill at 4k+, but when it flattens out or starts going uphill, her hard work allergy kicks in.
-Will accelerate and pull nicely up until the 4000 RPM mark, but will then hit that and get a little rough and try to die.
Secondary symptoms:
-Will run, accelerate, rev and do everything perfectly fine when the engine is cold, and for about 5 minutes after a hot start
-It will accelerate smoothly at WOT until 4000, then refuse to do more work than that.
-When it has this power/rev issue, and i'm on the freeway, put it in neutral, and then start the engine again, everything works perfectly for like 5 minutes, and then I have to repeat.
What I've done so far:
-Igniters are less than 1000 miles old.
-Brand, spanking, new fuel filter, and the fuel pump is less than 1000 miles old as well.
-Compression and vacuum lines are good.
-New spark plugs and I've checked the wires.
-Throttle body seems to be in working condition.
-Fuel is brand new, and all fluids are good
-Injectors cleaned, but not replaced
The only things I haven't checked yet are the sensors, carputer, and exhaust. Could it be one of those things and is there an easy way to test these to see if everything is working properly without having to take EVERYTHING apart?
Alright, Rotary Gods, differential diagnosis please! Any suggestions you have would be much appreciated.
Thankyouthankyouthankyou.
To begin with, I did search the forums using keywords like "sudden," "power," "loss," "dies," "WOT," "engine," and the such, and wasn't able to find a solution that I already tried.
The patient:
1985 GSL-SE, completely stock.
The symptoms are:
-Engine will only rev to 4500 after warmed up
-When trying to accelerate, engine just nopes out, and says "I feel like idling."
-Will maintain RPM and even accelerate a little when going downhill at 4k+, but when it flattens out or starts going uphill, her hard work allergy kicks in.
-Will accelerate and pull nicely up until the 4000 RPM mark, but will then hit that and get a little rough and try to die.
Secondary symptoms:
-Will run, accelerate, rev and do everything perfectly fine when the engine is cold, and for about 5 minutes after a hot start
-It will accelerate smoothly at WOT until 4000, then refuse to do more work than that.
-When it has this power/rev issue, and i'm on the freeway, put it in neutral, and then start the engine again, everything works perfectly for like 5 minutes, and then I have to repeat.
What I've done so far:
-Igniters are less than 1000 miles old.
-Brand, spanking, new fuel filter, and the fuel pump is less than 1000 miles old as well.
-Compression and vacuum lines are good.
-New spark plugs and I've checked the wires.
-Throttle body seems to be in working condition.
-Fuel is brand new, and all fluids are good
-Injectors cleaned, but not replaced
The only things I haven't checked yet are the sensors, carputer, and exhaust. Could it be one of those things and is there an easy way to test these to see if everything is working properly without having to take EVERYTHING apart?
Alright, Rotary Gods, differential diagnosis please! Any suggestions you have would be much appreciated.
Thankyouthankyouthankyou.
03-06-16, 12:23 PM
#3
84SE-EGI helpy-helperton
The '6-ports' are unlikely to kill power output at 4k RPM, as they'd just hurt top end performance, but it will still rev and accelerate.
My guess is two things, given the hot-engine and timing on when this happens; intake air temp sensors (2), or Airflow Meter. The weird timing indicates to me that the computer is running injection in open loop mode during cold startup, which it does to allow warmup and once that intake temp sensor goes out of range, it tries to modify fuel injector pulse map for an overly hot reading, which would lean out the top end to the point that it would starve out - VERY bad for the engine at higher RPM, or any RPM for that matter. Shutting it off and restarting will reset the computer and allow you to go to the startup fuel map for another interval. There are 2 intake air temp sensors, one built into the Driver side of the RE-EGI airbox, below the idle compensation circuit, and another at the Air Flow Meter. Which brings me to,...
Aif Flow Meter (AFM) needs to be checked to ensure the flapper door is moving freely and not binding. Do this by removing the air filer lid, the filter, and with engine off, use a pencil or a stick to push GENTLY on the air door. Feel for a nice, smooth movement, with no hitches or stoppage until you hear it clank on the stop pin. Any binding could allow the door to get stuck when heated by the exhaust on that side, preventing the air door from moving. This would 'fix' the amount of metered air coming in as reported to the ECU, and the computer would map injector pulse to match that limited flow. This would result in power loss, and kill acceleration as you described.
As an aside, the intake air temp sensors are compared between the AFM and Intake airbox to help the ECU map fuel, as a hot engine will show a greater differential between the two readings, indicating a leaner fuel map. One sensor out of range will screw this up and cause weird problems.
Lastly, and just throwing it out there, the coolant temp sensor on the rear of the waterpump also sends a signal to the ECU for fuel mapping purposes. Thats easier to replace and locate a replacement, as the intake air temp sensors are expensive and tend to break at the wire inlet to the sensor. Good luck, and post back with what you find,
My guess is two things, given the hot-engine and timing on when this happens; intake air temp sensors (2), or Airflow Meter. The weird timing indicates to me that the computer is running injection in open loop mode during cold startup, which it does to allow warmup and once that intake temp sensor goes out of range, it tries to modify fuel injector pulse map for an overly hot reading, which would lean out the top end to the point that it would starve out - VERY bad for the engine at higher RPM, or any RPM for that matter. Shutting it off and restarting will reset the computer and allow you to go to the startup fuel map for another interval. There are 2 intake air temp sensors, one built into the Driver side of the RE-EGI airbox, below the idle compensation circuit, and another at the Air Flow Meter. Which brings me to,...
Aif Flow Meter (AFM) needs to be checked to ensure the flapper door is moving freely and not binding. Do this by removing the air filer lid, the filter, and with engine off, use a pencil or a stick to push GENTLY on the air door. Feel for a nice, smooth movement, with no hitches or stoppage until you hear it clank on the stop pin. Any binding could allow the door to get stuck when heated by the exhaust on that side, preventing the air door from moving. This would 'fix' the amount of metered air coming in as reported to the ECU, and the computer would map injector pulse to match that limited flow. This would result in power loss, and kill acceleration as you described.
As an aside, the intake air temp sensors are compared between the AFM and Intake airbox to help the ECU map fuel, as a hot engine will show a greater differential between the two readings, indicating a leaner fuel map. One sensor out of range will screw this up and cause weird problems.
Lastly, and just throwing it out there, the coolant temp sensor on the rear of the waterpump also sends a signal to the ECU for fuel mapping purposes. Thats easier to replace and locate a replacement, as the intake air temp sensors are expensive and tend to break at the wire inlet to the sensor. Good luck, and post back with what you find,
Last edited by LongDuck; 03-06-16 at 12:26 PM.
Thread
Thread Starter
Forum
Replies
Last Post