Stumbled on this ignition timing vs. injector output vs. RPM table of a late model Chevy V8, specifically showing retarded timing with increased injector output.

 

So this table proves me that "Timing is advanced with increasing RPM and retarded with increasing manifold pressure (decreasing vacuum). When you ease the RPM up, timing will advance; when you snap it up, the first thing that happens is that it retards as the manifold pressure increases then advances as the RPM becomes the dominant condition." When throttle is suddenly opened manifold vacuum drops, injectors start to inject more fuel and timing is retarded (to avoid knocking I suppose). As rpm's go up timing is advanced. That's what I see in my scantool logs. So I'm pretty sure timing is not the issue

 

Did emissions check, passed with no problems. CO = 0, CH = 140. (Two years ago, when bucking problem wasn't there, emissions were: CO = 0,1 CH = 160). Still no resolution to bucking on acceleration problem, still waiting for any suggestions on what to check..

 

I've been on vacation for a couple of weeks w/o computer access (cruise) but have re-read the thread.

Will engine idle at all w/ IACV disconnected? Occasionally someone adjusts idle stop screw on throttle to change idle and this might cause idle stability problems due to air starvation at idle stop. Unsure if this would cause missing under load, but worth a try. Engine should idle at about 550 rpm w/o IACV. Manual does not specify a rpm w/ IACV disconnected.

Have fuel injectors been replaced?

Were you ever able to check fuel pressure under acceleration load? Missing/bucking under acceleration is definitely a symptom of low fuel pressure. Low fuel pressure under load could be caused by blocked fuel inlet screen, pinched fuel line, faulty fuel pump or fuel pump wiring, obstructed or fualty fuel pressure regulator.

You really need an advanced scanner to know whether miss is random or cylinder specific.

Finally, is it possible that there is no miss but only poorly restrained engine due to faulty motor mounts? Were they changed or inspected w/ engine swap?

Your perserverance is admirable and I'm confident it will be rewarded!

I can't wait to see the ending!

good luck

 

You posted some fuel trims with at different rpm. Was this at idle, or while driving? Try to capture LTFT and STFT when you try to accelerate under load and get the hesitation/misfire. Does you scanner have a misfire counter?

Was the fuel pressure regulator replaced when you did the engine swap?

If you clamp off the vacuum hose to the fuel pressure regulator, do you still get the hesitation/misfire?

 

LTFT at idle (@750rpm) is in 2.3 - 3.9 range. When driving @2500rpm LTFT is about 7. @3000rpm it`s about 0, if I remember correctly;

It's quite hard to get fuel trim data when car hesitates/bucks, because it lasts just a second or two, but O2 sensor clearly shows "rich" 0.9 volts at that moment, when I mash gas pedal to the floor, and it stays at 0.9V untill I'm at full throttle, so I highly doubt that fuel starvation is the problem, but who knows;

No, my scantool does not have misfire counter capability. But there is no CEL for misfire. When I disconnect injectors, I get misfire codes, so ECU can sense that for sure, I mean if it's a dead miss at least. I'm considering to buy honda HDS clone system, but still not sure if it will be money well spent. Took it to the Honda dealer a year ago to perform computer diagnostics with dealer tools (honda h.a.r.t. and HDS systems) - and they could'nt even connect to my car's ECU, which was fun, cause mine 10$ worth scantool has no problem there. ECU is not a problem, tried another one. They said maybe wiring between ecu and OBD2 connector is somehow broken, but I checked that and it's ok. And as I said, my cheapo scantool connects to ecu and reads data without any probs.

FPR was not replaced when engine was replaced, but: it's hose does not have fuel smell, when disconnected it does not have any effect on idle vibrations and bucking/hesitation when driving. But it has an effect on LTFT for sure - when FPR's hose is disconected, LTFT goes into rich mode (becomes negative to some degree) and that is normal as I understand - because fuel pressure increases with no FPR regulation at idle;

Engine will idle with IACV disconnected, but idle then becomes rapidly bouncy between 900 and 1100rpm if I remember correctly. Car becomes almost undrivable with IACV disconnected, there is no such thing as "idle screw" on F18B2;

Yes, fuel injectors were replaced;

I don't have tools available to check fuel pressure under load, but if O2 shows "rich" 0.9V under hard acceleration, and car can reach it's speed limit (like 205km/h or so) I just guess there's no probs here. One more thing - LTFT does not indicate "lean"condition;

Front mount was replaced with OEM one, others are in good shape. For sure no probs here;

Thank you for your support

 

Regarding idle control, throttle cable free play (lateral) should be 10-12mm). If not correct, adjust cable length (adjustment and lock nut) to obtain adjustment. Then adjust idle speed w/ idle air bypass bleed screw (TDC of throttle body) to obtain 770 +/- 50 rpm.

Above is unlikely related to your missing/sag response under load.

Your numbers for TPS (spec says 10% and 90%) look reasonable, but did you check for smooth change from idle to full throttle? A rough spot in the potentiometer of the TPS could cause rapidly varied TPS input and possible bucking/jerking.

All above is based on 98-02 2.2L Accord shop manual. I can't say if same for a 1.8L EU spec engine, but likely.

good luck

 

Well, throttle cable free play is just about right, so no problems here. F18B2 has no idle speed w/ idle air bypass bleed screw. IACV has full control on idle speed, which is just about right - 750rpm, and idle speed cannot be adjusted;

TPS voltage/resistance transition is smooth, checked that with DVOM and scantool. No dead spots.

 

Hello, sorry for my english.
Origami or solved this puzzle with a llamas because I have the same problem. I request information.
Regards

 

Hey did u find out what it is exactly yet because my 02 honda accord is doing the same exact thing