acceleration flat spots

[HondaFan81]

I've swapped out TPS on mine, it did not make a change. Also, I've tested the resistor box for injectors on mine and all is good, so I have not swapped that out. I have swapped out ignition coil with my other Accord that worked right, no change. I've swapped out fuel pressure regulators, nothing. Car has had a tune-up recent (dizzy cap & rotor, plugs, wires, fuel filter) and no change at that as well. I do not have an EGR system or vacuum box, except MAP sensor, so that rules those issues out. I sprayed everywhere in engine bay with carb cleaner and found no vacuum leak, my idle is consistent. I installed new OEM oxygen sensor, no change. Car runs leaner, gets better gas mileage like 2 mpg.

I have not swapped out MAP sensors, will plug in the other Accord sensor when I get a chance. I also want to do a valve lash adjustment, even though it is not due, just to make sure things are fine because that could affect vacuum being I have a Delta 272 regrind. I have to verify I have no exhaust leak, my car is fairly loud and I think it's louder than normal lately...I think.

[preludeman92]

I've swapped out TPS on mine, it did not make a change. Also, I've tested the resistor box for injectors on mine and all is good, so I have not swapped that out. I have swapped out ignition coil with my other Accord that worked right, no change. I've swapped out fuel pressure regulators, nothing. Car has had a tune-up recent (dizzy cap & rotor, plugs, wires, fuel filter) and no change at that as well. I do not have an EGR system or vacuum box, except MAP sensor, so that rules those issues out. I sprayed everywhere in engine bay with carb cleaner and found no vacuum leak, my idle is consistent. I installed new OEM oxygen sensor, no change. Car runs leaner, gets better gas mileage like 2 mpg.

I have not swapped out MAP sensors, will plug in the other Accord sensor when I get a chance. I also want to do a valve lash adjustment, even though it is not due, just to make sure things are fine because that could affect vacuum being I have a Delta 272 regrind. I have to verify I have no exhaust leak, my car is fairly loud and I think it's louder than normal lately...I think.

I decided to check the TPS before replacing it. It checked fine, even gave perfect reading while driving and when the problem occured.
I figured while I was at it, check the signal from the O2 sensor. The signal random, but never changes, even when the problem happens. The one thing I did notice though was the signal would range from about .2 to 1.8 volts. I thought they were supposed to range from 0-1 volts I'll go test the other hondas here when I get done with lunch. Oh, when the car went into fits, it the voltage from the signal wire was always about .56 volts May mean nothing though.
I may have to invest in the 14point7.com wideband kit so I can monitor the actual A/F ratio. It has the output of a narrow band sensor so the computer can actually use it to run.
I check the valve lash on 2 cylinders this morning, and it was well within spec.
I've checked for vacuum leaks... nothing. No exhaust leaks either.
I'm thinking the MAP isn't a problem, and I know the EGR isn't since mine doesn't exist either.
I changed the fuel filter, fuel pressure regulator, injectors, and resistor box, all to no avail. I checked the pump PSI, and it was spot on.
I put in new plugs, swapped wires with my accord, and check the cap and rotor for wear (there wasn't any). I just checked the coil for resistance readings, and it was perfect. I don't know or care I just want the car to be fixed.

[preludeman92]

Just got back from looking at the O2 sensor readings from 2 other hondas (90 accord and 91 prelude). They gave me readings I was expecting... ~.09 to ~.94.
That tells me that the other cars are perfectly healthy and the prelude that I'm having problems with has a bad O2 sensor or the wiring is bad somewhere. The wiring wouldn't really supprise me I had to hack it a bit when I did my 5 speed swap. However, I've checked my hacks multiple times and even removed them and made hard modifications to the wiring harness.

When I was monitoring the voltage of my prelude, the voltage started at about 10volts and slowly dropped to around 1 volt (+/- 1volt). It would idle about 1.1V and while driving would fluctuate between .34 and 1.7V but there would be extreme values outside that range.
When I monitored the readings from the healthy cars the reading started at about .03V and jumped around between 0 and 1 volt until the car warmed up. Once warmed up it would idle about .74V.
So to the 2 others that are having this problems, could you guys go check the voltage you're getting from the signal wire? It's a solid white wire going into and out of a connector on the shock tower. If your car is an original 5 speed the connector looks like an O2 sensor connector, but it will only have 2 or 3 wires going into it (it's also used for knock and IABs). It your car is an auto, the connector is a 12 pin one running the length of the car and is mounted on the side of the tower.

[preludeman92]

Sweet, I'm lost again. I swapped O2 sensors with my brother's prelude. His O2 sensor apparently dead since my car threw a code 1 within 3 blocks of my house. (I talked to him this AM and he confirmed it was dead before I touched it). I put my supposed broken sensor in his car and there wasn't a problem at all. I drove almost 55 miles on it yesterday and it never once acted weird or showed a voltage reading out of the ordinary.

[NAiL05]

Wow thats wierd. Something maybe wrong with wiring? Thats odd but yea usually stock o2 bounces from 0-1v unless y ou got some sort of wb its 0-5v. But thats just wierd.

[HondaFan81]

Sweet, I'm lost again. I swapped O2 sensors with my brother's prelude. His O2 sensor apparently dead since my car threw a code 1 within 3 blocks of my house. (I talked to him this AM and he confirmed it was dead before I touched it). I put my supposed broken sensor in his car and there wasn't a problem at all. I drove almost 55 miles on it yesterday and it never once acted weird or showed a voltage reading out of the ordinary.

Yea, that rules out the component, but o2 sensor wiring could still be the culprit. I'll have to monitor my o2 sensor readings as well, haven't done that. I've checked everything I could for a fuel related issue on my car. I'm more convinced that it is an ignition related issue. I'm going to swap out the distributor with my white Accord one (known good) and see what happens. If that doesn't help, I'll check o2 sensor readings.

When my engine power temporarily cuts out (always taking off from a stop) and I hear the engine/exhaust sputtering while cruising at times, it seems more of an ignition problem than fuel. I would think with fuel it would be more on/off.

[preludeman92]

I'm completely lost. I took my prelude down to the hardware store today and it was popping and backfiring like non-other. No smoke though. Maybe the cat stopped that though? I guess I really need to go beg my tuner make me a decent basemap for my hondata so I can datalog the car. I still haven't gotten it to work.
Also, I'm debating on buying the 14point7.com wideband to monitor what's going on and use that to feed the computer the narrowband signal.

Cisco, be sure to let me know if the distributor helps things. I would but I don't want to mess with wiring on my prelude or my accord since the accord is internal coil and the prelude is external.

[19accord92]

gahh... so no answer? i still think it might be the o2... im too lazy to change my o2 but i might sometime....

[preludeman92]

I ordered a wideband on monday. I'm going to intall it and and try to monitor what the a/f ratio is when the car throws a fit. I can use its narrow band output to substitue the honda sensor.
I haven't been in the car in better than a week. I'm just pissed off at it.

[ChIoVnIdCa]

I ordered a wideband on monday. I'm going to intall it and and try to monitor what the a/f ratio is when the car throws a fit. I can use its narrow band output to substitue the honda sensor.
I haven't been in the car in better than a week. I'm just pissed off at it.

I am having the same issue.. I lean out. I have done everything you have done and have a h22 though for some reason im thinking map..

[preludeman92]

Can't be my fuel map. 5 different stock honda ECUs all do it in this car but not others.

I've replaced the MAP sensor with another unit to the same results. I suppose I have to go read the voltage from the MAP sensor when I get a chance though.

[19accord92]

I am having the same issue.. I lean out. I have done everything you have done and have a h22 though for some reason im thinking map..

you have same issue and your car leans out? see... i got a fuel presure regulator and it doesnt have that acceleration flatspot as much as it used to... though it still has those spots... the car was running way rich b4 the fpr. and i turned fp to about 32 psi and it passed emissions, whereas before it was not passing emissions... but then again, i think that o2 controls whether or not we lean out or not right? gah i think i will finally splice that o2 sensor...

[203Cree]

If you're 02 sensor or wiring was bad it would automatically default the computer to open loop mode and make the car run on the rich side as a fail safe measure. So unless you're puffing black smoke like it's going out of style, I doubt it's that. Not to mention you'd get a code for it if it wasn't sending the signal it should.

Tell ya what, I have two theories that maybe you haven't looked at. Number one is the ingnitor box in the dizzy, number two is a possibly clogged catalytic converter. Normally if the cat is clogged it will produce too much back preasure in the higher rpm bands and cause the motor to fall over on it's face. You've got access to a spare car, try swapping the mid pipe. As for checking the ignitor, I'm not sure how to do that. You may also check your IAC valve. That could cause a lot of the issues at idle you mentioned. Without a PCV delete these things dump oil into the intake track like it's free.....

I'm interested to see what you find.

[preludeman92]

Cat is fine. It's new 10k miles ago and I took it appart as my first guess. I also know it's not my ignitor. I've switched them between 2 other running hondas and never had a problem. My problem HAS to be with the O2 and its wiring. The car has problems with known good sensors. However, as soon as I put in a known bad sensor (has a steady voltage out of .139V on 2 other cars, I get a steady voltage reading of 1.153ish volts in the prelude) the car no longer has issues. This is because (my theory anyways) the ECU stops looking at the O2 for a reading and subs in its assumed values. These values let it run well enough but doesn't get any of these weird flat spots.
I've got to have a voltage leak somewhere in my harness. The suspect bad sensor that I had in my prelude would give weird readings (up to 10V), but as soon as it's put in another car the voltage readings are perfectly normal. Once more, known bad sensors will give different steady readings in my car. WTF is wrong with that? I don't know, but the car is driveable right now.

[ChIoVnIdCa]

okay I just fixed mine. It was the IAT. Made a huge difference and no hesitation anymore