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Old 02-21-2002, 07:25 AM   #1 (permalink)
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Loss of power at after 3,000 rpm?

I seem to have this weird problem with 4th gen VTEC. After the car warms up and some driving, when I accelerate it pulls to 3,000 rpm and then all of a sudden it feels like its not accelerating as hard so I give it more gas and it just doesn't want to accelerate then it reaches 4,000rpm and picks up the power. This does not happen when the car is not fully warmed up. There are no weird sounds or vibrations while all this is happening. What could be a problem here?
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Old 02-21-2002, 07:31 AM   #2 (permalink)
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No check engine light?

What year?

Sounds like a fuel delivery problem. Try disconnecting the O2 sensor and see if the problem gets better or worse. I'm not sure "where" the car starts paying attention to the O2, but it's common for the ECU to dump a lot more fuel in during warmup. It might be that there's an a/f problem and the added fuel at warmup makes it better. This doesn't indicate the O2 as a problem, but it would tell you if it's a fuel problem (more than likely).

You might also try swapping MAP sensors with someone and see if the problem tracks with the MAP.

Other than that... make sure plugs/cap/rotor are OK, but it doesn't sound like ignition. I doubt it's the O2, it would probably lag all the time if it were.
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Old 02-21-2002, 07:47 AM   #3 (permalink)
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No check engine light. Also it doesn't happen all the time. This is a '94 VTEC. I seem to noticed this when I installed the DC header. I even reset the computer after install. I have new Magnecore plug wires and bosch spark plugs.
If it was my O2 sensor I would have gotten a code or something. A while back the car would throw code 13 or 23, not sure but I think it was 13, it never did since.
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Old 02-21-2002, 08:21 AM   #4 (permalink)
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I had somewhat of the same problem. Does the car kinda bog a bit? If it is your O2 sensor, you might not trip a code. Mine went and I didn't trip any code.

I would check the timing first. I basically replaced everything (O2 sensor, plugs, wires, cap, rotor, fuel filter, etc..) and nothing helped. Then I just decided to advance my timing, I got rid of problem. And yes, the car felt fast when it was cold, but when warmed up, it wouldn't pull at all. So check the timing, it's a free and simple fix.
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Old 02-21-2002, 08:21 AM   #5 (permalink)
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Quote:
Originally posted by vtecprelude
No check engine light. Also it doesn't happen all the time. This is a '94 VTEC. I seem to noticed this when I installed the DC header. I even reset the computer after install. I have new Magnecore plug wires and bosch spark plugs.
Did you do the wires/plugs at the same time? You might try going back to stock (if you still have them) just to try and isolate the problem.

Quote:
If it was my O2 sensor I would have gotten a code or something.
Not necessarily. You can foul an O2 so bad that your mileage goes to **** along with power... and the ECU will still think it's OK. The ECU is pretty bad about what it considers a "bad" O2 sensor.

My reason for unplugging it was to keep the car running open-loop. It's likely something with the a/f metering running a little lean in that region (or way too rich). If you go open loop (like when you're warming up) that might narrow it down. If not, it might be temperature-based, such as the engine coolant temp (ECT) sensor or the intake air temp (IAT) affecting the a/f ratio.

How bad is it? Are you sure it's not just a loss of low-mid power with the header? Does it pull nice and hard (harder than before) after 4 again?
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Old 02-21-2002, 10:30 AM   #6 (permalink)
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The plugs and wires were replaced wey before I noticed this problem. My timing is also advanced about 5deg. Most of time it pulls good but then all of a sudden the power just dies out it's not really that bed I can feel, so when I give it more gas it does not respond well then it hits 4,000 rpm and its though vtec came on it pulls really good. I seem to noticed this when I installed the header. I'm wondering maybe because the DC lower pipe is wider causing less exhaust flow over the O2 sensor therefore telling computer not to put more fuel in. But when there is no power loss the headers deffinetly added a nice gain over stock.
By the way the exhaust on the car is racing, it has no resonator, and the hole in the muffler goes straight into the pipe, so it has absolutely no pressure. Maybe adding the header causes too much back pressure loss.
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Old 02-21-2002, 11:21 AM   #7 (permalink)
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I would say no on the backpressure bit, only because the DC should present a fair bit of it at the collector. The wider pipe might be an issue, though.

The lagging could be knock, excited by something odd (like the header vibrating, or something). This might be improved by the additional fuel at warmup. You might try backing off the timing 5 degrees (back to stock), then maybe less than stock. This would at least help in narrowing the problem down.

If the plugs/cap/rotor were done a while ago, how many miles was it? You could have been close enough to edge with detonation that the plugs aging has increased the likelihood of knock. Slim chance, but still a chance. Maybe aggravated by the header and improved airflow.
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Old 02-21-2002, 12:07 PM   #8 (permalink)
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i'd go back with the oem wires and check the gapping on the plugs.

make sure the bracket for the header is secure as vibration can cause havoc with the knock sensor. had it happen with my hybrid accord and it wasn't fun.

i'd do a minor tune-up also, cap, rotor, possibly ignitor if you haven't replaced them out in a while.

check the o2
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Old 02-21-2002, 01:08 PM   #9 (permalink)
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The header bracket was well secured, I made sure of that but while I was installing the header I noticed the cat. heat sheild bolts were rusted on both sides where the exhaust is connected, so the heat shield was not holding on to well. During installation, I tried to move it and caused the to break loose, so now it is only being held on the header side and nothing securing it on the cats exit side. Sometimes when I hit the gas I hear a funky raspy sound, maybe it is heat sheild loose.
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Old 02-22-2002, 12:52 PM   #10 (permalink)
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UPDATE:

I went under the car and secured everything so there is no more vibrations coming from anything. While checking the plugs, I noticed that the spark plug from the cylnder that's closest to distributor had a very white tip and insulator when compared to all the others which were brownish color. From what I know this plug indicates that this cylinder is running too hot. What I also noticed is the plugs that were on the left side had the most wear on electrode. I would say the plugs needed replacement, and this is about 6,000 ml. on them. They are bosh platinum, I sure wan't be buying them again. I also went ahead and retarded the timin a few deg. After all this, the lagging that I'm experiencing still exists. This just sucks, I hate to know that my car is not running to full potential.
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Old 02-22-2002, 01:19 PM   #11 (permalink)
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if your plugs did have a white tip while all others were brown, be careful.

replace the fuel filter if you haven't done so in a long time or never since you have owned the car.

then have your injectors balanced and cleaned. you may have a clogged injectors. i've seen this happen with honda before. not a big deal. rc balances and cleans for $100. you can also ask them for a flow rate before and after.
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Old 02-22-2002, 03:02 PM   #12 (permalink)
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Quote:
Originally posted by vtecprelude
UPDATE:
While checking the plugs, I noticed that the spark plug from the cylnder that's closest to distributor had a very white tip and insulator when compared to all the others which were brownish color. From what I know this plug indicates that this cylinder is running too hot.
I can't tell w/o driving it, but you might be experiencing an anomoly with the header and your mods, interacting with the ECU. A V-AFC would be a good investment regardless, but it might really help you with eliminating this dead spot.

I think you're right on the plugs, though the brownish residue would make me think of something in the gas. Brown, not black? Sounds like octane booster or some other gas additive. A light great sooty appearance is normal.

Was the gap even on all of them (I know you said it looked like the LH side ones wore more)? I would be suspicious of the wires, at least enough to swap with another set. If that "hot" plug has a bad wire or mediocre contact... that might have something to do with the plug's appearance. Not too sure about the hesitation, though.
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Old 02-22-2002, 05:55 PM   #13 (permalink)
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Thank you all for your help.

I replaced the wires with Magnecore about 2 weeks ago, because one of the old wires was shot, so when ever I would accelerate it would hesitate and sound like one of the cylinders was not getting a spark. But this was fixed with new wires, so maybe uneven spark plug wear was due to bed old wires.

When I bought the car the first think I did was replace the fuel filter with Honda original fuel filter.

I have one of those haynes manuals which I bought for my integra, it has all the different plug symptoms. So by looking at the plugs and the pictures, the plug that came from the cylinder closest to distr. the white substance over it suggest that it is running very hot, cause;wrong plug, advanced timing or lean fuel mixture. Anyways, I switched the plugs and see if this happins again, I also put in Redline fuel system cleaner. I'll see how things go.

Something wierd I noticed, since my SRS light is on sometimes in that rpm range it very slightly dims and then goes back to normal.

Does anyone know if VTEC injectors same as SI?

If can't solve the problem I just might have to bring it to Honda dealer have them hook it to a computer and see what they can dig out.
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Old 02-22-2002, 08:34 PM   #14 (permalink)
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Quote:
Originally posted by vtecprelude
I replaced the wires with Magnecore about 2 weeks ago, because one of the old wires was shot, so when ever I would accelerate it would hesitate and sound like one of the cylinders was not getting a spark. But this was fixed with new wires, so maybe uneven spark plug wear was due to bed old wires.
I've seen Magnecore wires cause a problem by not snapping on/down all the way. Something to consider, though with r/r during plug check I would think that would be eliminated.

I think you're right on the plugs. The brown stuff might have been the redline if it was in there at the time. The plugs should normally be an ashy gray color.

Quote:
Something wierd I noticed, since my SRS light is on sometimes in that rpm range it very slightly dims and then goes back to normal.
That IS odd. I would suspect an alternator or battery problem, causing the system voltage to drop. That would be odd, though, to occur mid-band and then go away up top. REAL wierd.

Quote:
Does anyone know if VTEC injectors same as SI?
I'm pretty sure they are not. The VTEC motor should require a good bit more fuel on the top end.

Quote:
If can't solve the problem I just might have to bring it to Honda dealer have them hook it to a computer and see what they can dig out.
I doubt they will dig out much, especially if it's OBD1; those computers stored/reported a lot less. I've taken in a car before for diagnosis, though, just to get the diagnosis ("Ah, no thanks, I think I'll just live with it." As I drive off to buy parts ).
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Old 02-24-2002, 07:55 PM   #15 (permalink)
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I've re-checkt the Magnecore wires and they all snapped in. Since it feels like something is retarding the timing and one of the cylinders running too hot based on the spark plug which probably causes the computer to sense a knock and retard the timing,

I was wondering can I drive the car if I unplug the knock sensor and also map sensor?
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Old 02-25-2002, 06:54 AM   #16 (permalink)
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You should be able to but you will run open-loop in "limp" mode. Chances are the car will run worse, but I don't see what doing that will do for you.

Now, if you swapped the parts in from known good spares... then that would tell you something, if it fixed your problem.
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Old 02-25-2002, 07:41 AM   #17 (permalink)
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I had this same problems for about 6 months. I had no idea what the hell it was. I had taken my car in to get the timing belt changed. While they did the belt i had them take out the AEM cam gears for my stock ones because AEM gears are cheap and i was not pleased with them at all. I also ordered a O2 sensor for them to put in while they were under the car as well. Ever since then, my car hasn't hesitated once. Even when driving it for hours. I had the same exact problem as you. My car was fine when it was cold/initially warm but once it started to warm up fully the car was boggin annoyingly after about 2500rpm all the way up to 4000. And when it hit 4000 it was like VTEC was kicking in like you said. If i were you i would try changing out the O2 sensor then reset your ECU after the install. It's a little bit of an expensive fix but it could work.
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Old 02-25-2002, 11:20 AM   #18 (permalink)
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Re: Loss of power at after 3,000 rpm?

Quote:
Originally posted by vtecprelude
I seem to have this weird problem with 4th gen VTEC. After the car warms up and some driving, when I accelerate it pulls to 3,000 rpm and then all of a sudden it feels like its not accelerating as hard so I give it more gas and it just doesn't want to accelerate then it reaches 4,000rpm and picks up the power. This does not happen when the car is not fully warmed up. There are no weird sounds or vibrations while all this is happening. What could be a problem here?
It may be the catalytic converter. Have you run a back pressure and temp test?
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Old 02-25-2002, 07:41 PM   #19 (permalink)
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I did not run a a back pressure and temp test.

I removed the oxygen sensor and then sprayed it with tb. and brake cleaner. After the installation, I took the car for a drive and it started bogging pretty bed after 2,000 rpm and after some driving it gotten a little botter but still I was back to the same problem. I think there is something wrong with the oxygen sensor. So I will be replacing oxygen sensor anyway since my car has over 100,000 ml. I will let you all know what happins.
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Old 02-26-2002, 06:24 AM   #20 (permalink)
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Sounds like the O2 sensor would need to be replaced then, if not just as a result of your "cleaning." Don't even bother cleaning O2 sensors... you can't do it (at least, it doesn't work).
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