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Engine stumbles bad when you decelerate and then try to accelerate

Car: Honda, CRX HF, 1991     -    Back to Fix-It    -    Honda CRX HF Repair Manuals

Q.1991 crx hf -all stock. Engine stumbles bad when you decelerate(come down hill) and then try to accelerate. It will idle fine, and when you try take off it stumbles untill thottle is blip several timesand then runs fine untill next decel. any help PLEASE

I already checked/done: plugs cap rotor

Answer Greetings! You could have a bad oxygen sensor. The oxygen sensor is very important to control not only the cars emissions but it also helps the vehicals performance! If it is not working properly it can result in a number of problems like rough running stalling hesitating bucking and jerking. But more common than that if it is lazy, the cars gas miledge can drop considerably, and sometimes not even set a check engine light on the dash!
The fuel control Heated Oxygen Sensor (HO2S 1) is mounted in the exhaust manifold where it can monitor the oxygen content of the exhaust gas stream. The oxygen present in the exhaust gas reacts with the sensor to produce a voltage output. This voltage should constantly fluctuate from approximately 100 mV (high oxygen content - lean mixture) to 900 mV (low oxygen content - rich mixture). The heated oxygen sensor voltage can be monitored with a scan tool. By monitoring the voltage output of the oxygen sensor, the PCM calculates what fuel mixture command to give to the injectors.

Addition If o2 sensor was bad wouldn`t that through check engine light ???

Answer Eventually it should.
Also, your throttle body may be carboned up and need to be cleaned! This can cause all sorts of idle and hesitation problems. This is caused by the throttle plate not seating properly. The First thing i would do is clean out the throttle body with some throttle plate and intake cleaner and a small brush. Another common cause would be the Idle Air Control motor. It may be bad causing your condition. This is very common on older cars. The IAC motor gets lazy and cant keep up with the fast idle changes. Also when the IAC motor is out, I rec to check the passages for carbon build up. If they are plugged they need to be cleaned out.
Check for the following conditions:
Poor connection at PCM or IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Diagrams.
Damaged harness. Inspect the wiring harness for damage.
Restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system.
Throttle body. Check for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate. Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects which will not allow the IAC pintle to fully extend.
Vacuum leak. Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at EGR valve and EGR pipe to intake manifold, leaks at throttle body, faulty or incorrectly installed PCV valve, leaks at intake manifold brake booster hose disconnected, oil filler cap, oil level indicator loose or missing, etc..

Addition Throttle body and plate was cleaned all vacumm ports also cleaned. Egr removed cleaned- new gasket -diaphram working good. Also brand new Bosch o2 sensor installed. Checked for vacuum leaks- None. Intake from filter to throttle body free and clear. Still has issue.........

More Info required Have we checked for codes in the computer?
What is engine vacuum at idle?
WHat about ignition timing?

Addition No codes- recently baterry disconnect. I don`t have vacuum tester or timing light. Since engine runs great 95% of the time, wouldn`t think these are my issues. Agree or not ??? I`ll drive it more, hopefully it will give code.

Answer Engine vacuum would not normally come and go. However, I have see the key way on the crankshaft sheer and the harmonic balancer be way off. Because this key way holds the timing belt pulley and both the harmonic balancer in place, if this one thing if off, it can cause two problems. Not only that, when the engine is running, the two can be shifting around causing an intermittent problem. That is why I just wanted to get a big picture of what is going on here.
I know you said it idles fine, but this sounds like the IAC motor is starting to get lazy.

Addition Still have no codes, no check engine light. If key sheared off crank balancer it would move freely. No play there..I`ll see if my book has specs on IAC.

Answer Well the vehicles that I have come across with the key way sheered, the balancer was still pretty tight. It just moved when there are severe engine speed fluctuations like starting and stopping.
Did you get a vacuum gage?

Addition I`ll double check balancer tomarrow. No vacuum gage yet. Work is busy. I`ll get there...thanx.

Addition Still no codes, drove car with timing light in car, when she hesitated timing light went black. I`m thinking distributor, since all grounds and connections are clean and good. What do you think??

Addition new distributer still falls flat -after coming down long hill and try to accelerate.

Answer I know this may be hard, but does it help if you where to spray some starting fluid into the intake when this happens? Try to get ot act up when you are in park. Sounds silly, but maybe if you can duplicate the same conditions and then have somebody spray starting fluid into the intake when this happens. If it helps and the engine comes alive, then we know its a fuel issue.

Addition This problem only happens when driving down the road. So spraying ether is out of the question. Is it possible ecu sparatic miss fire ??

Answer I would lean towards no. I have never seen that happen or heard it it either.
If you can back probe the o2 sensor and get a volt reading from it when this happens, we might be able to find out if we are running too lean causing your problem. Just run a small wire along side of the hood/fender while driving. I do this all the time. Just be sure the voltmeter is grounded.

Addition Hooked wire to o2 sensor, meter reading fluxuated greatly while driving. Under hard throttle when up to (.945) dcv. Usaully under coast in gear would drop (.125)But these readings would fluxuate. And under stumble it would read (.578).Only would be consistent after key off-it would slowly and steady drop .

Answer The first two reading are perfect! That is what we are suppose to have! The other fluctuations are going to be normal.
As far as the .578, this would indicate not too lean or too rich. Now if you had the gas pedal all the way to the floor when it was reading only .578 that would be a bit too lean. Why? Because you need a lot more gas to accelerate so the exhaust should be rich. You are going to want to see full rich .900 or more.
Even with the o2 sensor disconnected, does it still stumble on acceleration after coasting?
Try disconnecting the o2 sensor and see if it still happens. This should put the computer into closed loop which should give us more gas.

Addition o2 disconnected, drove car all day NOT ounce did she fall flat, slight hesistation in 1 and 2 gear unless foot was deep in pedal. Much better what does this mean? Check engine light on as expected....

Answer Are we sure the o2 sensor has been changed? Your not fibbing me are you? If it has not been changed, we need to change that 02 sensor!

Addition Brand new bosch, back when we first talked

Answer Did you put that o2 sensor in because of this problem?
Maybe its bad? Do you think you could get it warrantied for testing purposes?

Addition I put new o2 in. It was $35 and I figured it`s worth a try. Electrical parts are very hard to return, I dought they would. If nothing else could be the issue, I`ll purchse another one. Just don`t want to waste money.

Answer NO.. I just was not sure if the problem has happened ever since the o2 sensor was put in. But since the problem was there before the o2 sensor and did not change when the o2 sensor was replaced, then chances are its not the o2 sensor.
One idea is that the o2 sensor grounds itself through the exhaust system. Even though the exhaust is bolted to the engine, sometimes it needs an extra ground. Look on your exhaust system for a small wire that clips onto the exhaust from the body. They do this in the early 90's.
Assuming the o2 sensor is good because it new, the reading that it comes up with when the stumbling occurs is too lean. Its only .5 volt. Now, if fuel pressure is good when this happens, that would rule out fuel pump, filter and voltage to the pump. The only other things that could be left is the injector, or not enough injector pulse wight. To look at injector pulse width, you would need access to a scanner. While this problem happens, you would need to look at injector pulse width on the scanner and be sure it matches injector pulse width when you are under full accel and everything is working just right. If those two match and we still are not getting enough fuel, my money is on the injector in the throttle body. But if the injector pulse width is low, we will have to look at the inputs to the computer such as map sensor and tps sensor very close.

Addition I`ll throw xtra ground on, my injectors are multi port not throttle body. My thinking is it never stumbles under hard acceleration wich would rule out fuel pump. I`m thinking electical somewere, and does not throw a code. Everything electrical thats not happy, sends message to ecu. TPS I belive does not throw a code, if so can I check this? I`m just not well equiped with a arsenal of meters and gauges. Hope I can keep car out of Local Honda center.

Answer You can sweep the tps with the key on.
The Throttle Angle Sensor, connected to the side of the throttle body, is a rotary potentiometer. It is connected to the throttle shaft. As the throttle angle changes, the throttle angle sensor varies the voltage signal to the ECU. The ECU uses this voltage signal along with the MAP Sensor voltage signal to determine engine load. The typical output voltage at idle is approx. 0-0.5 volts and at wide open throttle approx. 4.5 volts.
If there is any spike or sudden abnormal voltage change when your slowly opening and closing the throttle, the tps is bad.

Addition Sweep with key on, does this mean check with key on engine off? Also TAS has three wires (green red stripe)(red blue stripe) (yellow). Which one. Also do I strip a little of jacket? Also what I thought was TPS my book says is EAVC. Were is TPS? It also gives me resistance #`s that it should be at. I`ll check tommorow night. If I`m talking nonsense please set me straight. Thank you for your patience.

Answer NO... check with key on.
Red and blue wire.
Tps is on the throttle body. No resistance... voltage specs we are interested in.

Addition Red&blue .8 volts closed = 4.6 wideopen. I also check voltage EACV plug, blk&yelw = ble&yelw 12 volts which my book says no voltage should be present. Possible ecu faulty. What do think??? Also 21 IN vaccumm at idle (constant)

More Info required Vacuum sounds good!
Is this blue & yellow wire the signal wire or ground?

Addition book says black/yellow (+) blue/yellow (-) EACV.

More Info required Didn't we replace the eacv?

Addition NO...Dealer part fairly expensive....

More Info required Maybe this is your problem?
Can you get one from a junkyard just to try it?

Answer If we can get access to a scanner, I have a neat little tool that will narrow your problem down. Its called the flatter test drive. I know it works well for obd2 cars, but I don't know how well it will work for obd1 cars. But its worth a shot. Here it is
Wide open throttle for at least 5 full seconds.
Pre cat o2 sensor should go full rich.
Baro pressure should remain the same.
engine load should go to 100%
RESULTS
1. Poor acceleration, rich exhaust, good baro = restricted exhaust.
2. Poor acceleration, rich exhaust, low or decreasing baro = restricted intake.
3. Poor acceleration, lean exhaust, good baro = fuel delivery concern.
4. Poor acceleration, lean exhaust, and low baro = air flow measurement error.
(This is a rule of thumb. Not always the case) But I have found it to be very Acurate. We must find out which one of the 4 yours fits into when this problem happens.

Addition I`ll try some junk yards, that might be easier for me than flatter test .

Answer Sounds good!

Addition Having trouble finding a yard that has one. There`s one on EBAY that came off d16 motor mine is d15. I think difference is 1.6 ltr versus 1.5 ltr. Do you think there the same part (eacv)

Answer NO... I would think they are different.

Addition Here`s what I did, new fuel pump-used ecu-used fuel pressure reg.- all wich did nothing. I unplugged TPS (throttle angle) and car ran great for days no stumble and idle was steady only problen engine light on.

Answer Well with the tps sensor unpluged, the check engine light will be on.
Sounds like the tps might be bad.
Did you try a new one?

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