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Hello, and excuse me for my english in advance. The car is 2002 Honda Accord 1.8l, engine code is F18B2. The problem is, that my car jerks/hesitates when I fully depress gas pedal and then floor it. It does not matter if the engine is cold or hot. The car violently jerks a few times, then accelerates normally. It happens at any rpm. It is more felt in low gears, less in high gears. Another thing is, that when i try to keep constant speed in low gears (1-st ant 2-nd at 1000-2500rpm) it hesitates and it’s hard to drive in traffic jams, because i have to use the clutch very often. Idle is a bit rough, engine seems to misfire from time to time. When cruising at high speed nothing wrong is felt. Also if changing gears very softly and not accelerating hard everything is almost o.k., almost no jerking/hesitation is felt. CE (MIL) light is NOT on. Changed: air filter, fuel filter, plugs NGK, wires NGK, cap/rotor/coil, then tried another distributor from salvage yard. Nothing changed. Cleaned EGR valve and ports. Did put in the new O2 sensor (NTK). Did the valve adjustment. PCV valve is O.K. Tried disconect any sensor that is present in this engine (TPS, MAP, IACV, IAB, EGR, KS, so on), reset the ECU/PCM, then test drive – nothing changes or gets worse. Cleaned IACV. TPS reads 0.5V at closed throttle and 4.5V at WOT. Voltage transition is smooth. Tried another MAP sensor. No luck. Engine idle rpm ‘s are OK, they do not jump around. Compression in all cylinders is 14.5-15bars. No white smoke, coolant level is constant. Eats some oil, but the eating rate is constant and it allways ate some oil. Ground wires to the engine are cleaned and ok. No vacuum leaks I did found. Maybe somebody here knows the solution?
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If you have or can get one, hook up a scan tool and check for codes (I know the MIL light is off, but you still may have codes (light only comes on if the engine is polluting 1.5 times the maximum allowed standard)) also see if you can get fuel trim numbers (long and short) for idle, 1,500 rpm, 2,500 rpm and 3,500 rpm.
It has been hooked to the scantool. No exesive engine pollution found, CO & NOx numbers are ideal. No error codes even with scantool hooked up. Timing is ok, 12 degrees as it should be at idle. Timing is controlled only by ECU, there is no way to change it by rotating the distributor, cause it does not rotate when the two bolts which holds it to the head are losened. I will try to hook up a scan tool again to get fuel trim numbers, but it can take some time, i don’t own scantool. Mileage is 157.000km.
Normally bucking on acceleration is a secondary ignition issue, but you have replaced all the secondary ignition. In cases where it is not related to secondary ignition, I have seen MAF sensor issues trigger a bucking acceleration.
To see if that is it, I kinda need the fuel trims and MAF grams/per second PIDS at idle and wide open throttle. Unplugging it won’t let you know if it is the problem on a Honda because the PCM does not have a back up speed-density subsystem to relay on. On a GM if you have a suspected bad MAF you can unplug it and the PCM will revert to using a speed-density formula, if the vehicle runs better the MAF was bad, cant do the same on a Honda. On a Honda the PCM substitutes a fixed calculated valve and goes into a limp mode which is no where near as smooth as a properly running system.
You could have a MAF that is under reporting the amount of air coming through the engine. So when you give it gas the computer does not advance the timing enough and add enough fuel to meet the demand. That would cause the spark to come to late and the power would fall off. You replaced the MAP already, but if the MAP works fine, but the MAF is off the PCM will have a hard time controlling its idle.
If the MAF is off it should show up in the datastream, when you mash the throttle down at idle the MAF should show more than 100 grams of air per second.
I have never seen MAF sensor on Hondas, but maybe in newer models they started to show up. Mine certainly has only MAP, and i have tried to replace it, but nothing changed. When ignition is on, but car is not started, MAP sensor gives about 3V on output to PCM, on idle about 1V, just like it is stated in the manual. One more thing – if gas pedal is fully released, then pressed a little bit, and only then floored – there is almost no jerking. But if I fully release it and then suddenly hit the pedal, jerking is quite violent. Also I am considering to buy some scantool on ebay – it would be nice for it to be not too expensive and work well with Hondas, i quess some freeze frame/data logging thing would help in this situation, so maybe there is some scantool of certain brand/model that you would recommend?
Spark plugs look like this now: http://i39.tinypic.com/2vxlqu0.jpg http://i40.tinypic.com/2evqeex.jpg I guess cylinder 2 runs lean. But i can’t find any air leaks..
Check for air leaks in the tube that goes from the air filter housing to the throttle body. Any air leaks here can cause performance problems. What you describe is almost a classic indication of this problem. As you accelerate the engine moves, and opens the hole wider which lets in more air that the MAF sensor did not account for.
More info here.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted.
[quote=”origami” post=80986]I have never seen MAF sensor on Hondas, but maybe in newer models they started to show up. Mine certainly has only MAP, and i have tried to replace it, but nothing changed. When ignition is on, but car is not started, MAP sensor gives about 3V on output to PCM, on idle about 1V, just like it is stated in the manual. One more thing – if gas pedal is fully released, then pressed a little bit, and only then floored – there is almost no jerking. But if I fully release it and then suddenly hit the pedal, jerking is quite violent. Also I am considering to buy some scantool on ebay – it would be nice for it to be not too expensive and work well with Hondas, i quess some freeze frame/data logging thing would help in this situation, so maybe there is some scantool of certain brand/model that you would recommend?[/quote]
You are right, I looked up your engine code and there is no MAF.
Looks like the UK version of the Accord is a MAP speed density system and the American is the MAF controlled design.Have to tried to get a fuel pressure reading yet?
Tube from the air filter housing to the throttle body is in mint condition, no cracks, holes or whatsoever. No MAF, MAP sensor only. Lean misfire happens in cylinder 2 as I understand. Look at the spark plugs: http://i39.tinypic.com/2vxlqu0.jpg But I can’t find any vacuum leaks, injector seals are good, intake manifold gasket is o.k. too. So I suppose problem is in the valves most probably. But then – why compression is good in all cylinders? Fuel pressure and injectors are o.k. Maybe PCM/ECU sends leaner mixture to that particular cylinder? But I think it’s hardly possible. Resistances between ECU connector and fuel injectors are good and even. So I quess the best option is to try leakdown test in some shop, because I suppose compression test does not 100% warrant that cylinder 2 really seals properly…
[quote=”origami” post=82055]Tube from the air filter housing to the throttle body is in mint condition, no cracks, holes or whatsoever. No MAF, MAP sensor only. Lean misfire happens in cylinder 2 as I understand. Look at the spark plugs: http://i39.tinypic.com/2vxlqu0.jpg But I can’t find any vacuum leaks, injector seals are good, intake manifold gasket is o.k. too. So I suppose problem is in the valves most probably. But then – why compression is good in all cylinders? Fuel pressure and injectors are o.k. Maybe PCM/ECU sends leaner mixture to that particular cylinder? But I think it’s hardly possible. Resistances between ECU connector and fuel injectors are good and even. So I quess the best option is to try leakdown test in some shop, because I suppose compression test does not 100% warrant that cylinder 2 really seals properly…[/quote]
Best way tyo determine if you are running lean is to get a scan tool that can read fuel trims.
Fuel trims tell you if the ECM is adding fuel or removing fuel to compensate for a rich or lean condition.
The fuel trim value will show LT (long term) and ST (short term).
this video should help you understand how fuel trims work.
If you are trying to diagnose drivability issues but don’t have any trouble codes to chase, take a closer look at the vehicle’s “fuel trim”. When analyzed properly, it can be a valuable diagnostic tool, a window to the heart of the Fuel control system and how it is operating.
Understanding Fuel Trim
A vehicle’s computer system uses Fuel Trim to help maintain the ideal air/fuel ratio for complete combustion (stoichiometry) – 14.7 parts air to 1 part fuel. Three way Catalytic converters need the mixture to be constantly driven rich/lean around this ratio in order to work at maximum efficiency. Fuel trims can compensate for other vehicle issues. That’s why fuel trims are so useful. They can provide an overall picture of what is causing the problem such as an intake manifold vacuum leak (positive fuel trim – lean) or a stuck open fuel injector (negative fuel trim – rich).
Short Term Fuel Trim
Short Term Fuel Trim (STFT1 and STFT2) is the computer’s immediate response to adjust the air/fuel ratio. In positive corrections, fuel is added to adjust for a lean condition, while negative corrections respond to a rich condition. STFT corrections represent the current engine run cycle and react very quickly to O2 sensor input. If you were to create a large vacuum leak at Idle by disconnecting the PCV hose, the computer would immediately add positive fuel trim to balance the mixture. Short Term Fuel Trim is not stored in Keep Alive Memory (KAM) after shut down and automatically resets to 0 for the next start/run cycle.
Long Term Fuel Trim
Unlike STFT, Long Term Fuel Trim (LTFT1 and LTFT2) is learned over time while in closed loop operation. It is stored in the KAM and also used for open loop fuel calculations (like start up and wide
open throttle). LTFT is a coarser adjustment and also works to keep STFT within specification.
Diagnosing with Fuel Trims
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
Diagnostic Tip:
For a suspected vacuum leak, note the fuel trims at idle and increase engine speed to 2500 RPM and hold. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, you have a vacuum leak. After the repair, reset the KAM and start the vehicle. Monitor the fuel trims to make sure they are within the normal ranges. It could take up to 10 miles of driving for an accurate LTFT reading.
Collecting and Understanding Scanner Data
In live data, find the Long Term (LTFT 1 and LTFT 2, etc/) and Short Term (STFT 1 and STFT 2, etc.) Fuel Trim information. In OBD II GLOBAL, the fuel trim data will be presented as a positive or negative number with ZERO being the center point (1). A fuel trim of 0% is perfect, but unrealistic, some amount of trim will always be acceptable, and even required by the ECU (electronic control unit) or PCM ( power train control module).The OBD II parameters for fuel trimming are generally 25% either positive or negative before setting P0171, P0172, P0174 or P0175 codes, but catalyst codes will be set long before the trim gets to those numbers.
When adding the long term trim to the short term trim, you obtain a basic “total trim number”. This number should be very close to zero, never exceeding 10% positive or negative.
For example, A LTFT of 3% and a STFT of 1% would give a total trim of 4% which is within the normal range.
Negative numbers can work in your favor as well; for instance, the STFT is 4% and the LTFT is -2%, the total trim number would be 2% which is near perfect. The same thing if the total trim number wound up in the negative.
A number close to zero is fine, but 10% negative or positive is out of limits.
Now, besides the total trim value being well below the 10% threshold, the spread between the long term and short term fuel trim values must be as well.
As noted above, adding a negative number to a positive number can get you closer to zero which is a good thing, but if the spread is too large, you need to find out why.
For example, LTFT is 7% and STFT is -7%, well that would give a total trim number of zero which is “perfect”. However, the spread between the numbers is 14% which exceeds the target “10%”. While it is true the total trim number is zero, it’s a bad way of getting there. It is an indication that the PCM (power train control module) is not in complete control of the fuel injection, it’s scrambling to make up for an issue that is nearly out of its control. If the vehicle utilizes mass air flow (MAF), this condition STRONGLY suggests Mass Air Sensor issues. If the vehicle utilizes MAP (manifold absolute pressure sensor), check the vacuum at the MAP sensor.
Suppose that the numbers are all well within the target 10% limits at idle (remember, that doesn’t mean 9% is good, just that the numbers may not have exceeded 10% yet). You should now make certain that there is no fuel starvation issues occurring.
Hold the engine RPMs up around 2500 for a minute and observe the trim data once more. (Hint:) if the numbers don’t change, that would be very suspect. Short term trim will usually be moving all the time, but if your Long term trim doesn’t change from idle to 2500, you need to investigate further. (This does not hold true for VW and Audi, their Long Term Fuel Trims will not change unless the vehicle is moving at a cruising speed).
Now check your results.
If the numbers are well within 10%, replace the converter along with the upstream oxygen sensor — you should not encounter any further problems. Remember, oxygen sensors have a useful life of approximately 80,000 miles. Even if you went to the trouble of connecting a digital scope to the signal wire and observed the sensor switching across 450mv within the 200 millisecond parameter during a drive, what happens when the sensor exhibits a slowness to switch due to age and deterioration, allowing the vehicle to run rich for too long a period? It could destroy the new converter. So, ALWAYS replace the upstream oxygen sensor when replacing a converter unless you personally know the sensor has much fewer miles on it.
If your results are NOT within the 10%:
A positive fuel trim denotes a lean condition. A lean condition can mean too much air (un-metered air), or an insufficient amount of fuel.
A negative fuel trim denotes a rich condition. A rich condition can mean too much fuel, or an insufficient amount of air.
If your fuel trim # keeps increasing (leaner) as your rpm increases, you should suspect fuel delivery issues or a massive amount of unmetered air. (ex. bad Evap Cannister).
If your fuel trim is lean at low RPM, but decreases with an rpm increase, a small vacuum leak could be suspect.
Good call on the fuel trim data, and thanks for the info on the MAF sensor. Just for the heck of it, try spraying the ignition system with water while the engine is running. If it starts to act up, perhaps there is an ignition system problem and not a fuel system issue.
Tried this before I put in new NGK plugs, NGK wires, cap, rotor, coil. Then tried another distributor. Nothing changed. Mechanical timing is ok, all marks are where they supposed to be when cyl n.1 is at TDC. Scan tool shows 12 degrees on idle, as it should be. Timing is advanced or retarded only by ECU. I’m almost 100% sure that problem is not in the ignition system. I’m thinking about leakdown test, but I’m not sure if it’s worth to waste money doing it because compression test shows about 15 bars in all cylinders (~217PSI). I did repeat compression test a few times. Coolant level is constant, so gasket is not blown i suppose. Maybe valves or rings? Maybe compression test is not 100% guarantee that cylinders seal properly? Idle is rough, but when I give it some gas on idle, engine smooths out. All cylinders work, tried power balance test. Mosly I’m concerned about spark plug color in cylinder 2. looks like this: http://i39.tinypic.com/2vxlqu0.jpg It’s alot brighter than the other three, indicating lean condition in that cylinder. When i release gas pedal and then give it some, it bucks a few times like hell, then accelerates nomally. And when i suddenly release it, some bucking is felt too. And on low gears when trying to keep constant low speed, like in some parking lot, it hesitates too. When cruising on a highway at constant speed – everything is ok. Gas/mileage dropped, and some power too. Still waiting for a scan tool to arrive..
Well done ruling out the ignition system. It’s rare that Honda’s have fuel delivery problems. That said, they do have vacuum leaks from time to time. You might check for a vacuum leak at cylinder #2 intake gasket. Given that you don’t have a problem at cruse speed, this might be a good theory to look into. Intake leaks often cause issues with idle and low end performance but go away at higher rpm’s.
I’ve tried to spray carb cleaner pretty much everywhere around intake manifold – gaskets, injector o-rings, vacuum hoses – to no effect on idle speed. I’m almost sure there’s no vacuum leak too
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