Backfire/Studder under acceleration

Richard808:
The new coil came with a new boot. I have replaced all the boots anyway so i'm sure its not the boots. Also, I made sure the wires are in proper configuration, that's a different problem.

Drcoffee:
I have looked at rockauto.com and saw those but I think you have to buy them in sets of 6, I could be wrong though. I wish I had the money to do them all right now but i have a big trip out to North Carolina next month and cant spare that much cash, probably after though.

As far as the plugs are concerned, I have replaced those with brand new ngk double ground platinum's along new ngk wires.

I might give that method that spectre6000 mentioned later today if i can convince myself its not going to break anything lol. I disconnected a plug the other day and started it up and it was shaking pretty good which had be a bit concerned cause that was at idle. I'd have to rev it up to 2500 to confirm that that cylinder is at fault and I may have to do that up to 6 times, it gives me cause for concern.
 
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The problem I can see is that you don't know which injector is giving you trouble. And you can buy single injectors at rockauto. I bought 3 and sent the other 3 to witchhunter to rebuild. One had a dead coil so I only got 2 back in working order. I would prefer to send them to witchhunter but there is less down time with rockauto.

I wouldn't rev the engine with a plug wire removed. I think that's what you were suggesting.

With all 6 plugged in, you get a baseline for how the engine is running at idle. Then, one at a time, disconnect a plug wire from the plug and watch for any change in idle character. IT SHOULD MAKE THE ENGINE RUN WORSE. If you pull a plug wire and there is no change, then you found your dead cylinder.
 
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it runs perfectly fine at idle, it is smooth and normal all the way up to about 2500rpm, thats the problem. If i had one cylinder out this whole time I would have had this figured out a long time ago. The issue i'm having is it acts fine, drives fine but once i rev it up to and around 2500rpms, it hesitates and and shakes really bad.

I cant test it the way spectre6000 has mentioned because the problem does not exist at idle, it only exists around 2500rpm. If it is an injector, its acting like it is on its way out but hasn't quite made it there yet or one of them has gotten partially clogged and it can deliver enough fuel at idle and low speed driving but under higher pressures it cant deliver the fuel required.
 
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I didn't read thru all 5 pages of the posting, so someone might have already covered this, but thought I'd throw this in, as I had very similar symptoms on my '99 3.4 recently, after running the gas tank too low. (dumb to do, I know!)

I think I sucked some crap thru, to the injectors and it was doing the same thing- it would start/idle fine, but uner load (ie giving it gas while in park, or actually trying to drive it...), it would bog and chug along.

It was running really lean (ie no black smoke or fuel smell...) and I was also getting a 'backfire'/popping noise, coming off the down pipe/Catalytic area.

I used a bottle of Chevron Techron fuel treatment and I filled up w/Shell 93 octane and it still took a good 10-15 miles of driving, for the symtoms to go away.

Just throwing this out there, in case you ran your tank low like I did.
 
'99-4Runner:
that sounds pretty spot on what symptoms i am having. I have already added that exact same cleaner into the tank and have debated on whether or not i should try another. I'm also considering taking it to a local shop to have the injectors cleaned
 
T4RFool said:
it runs perfectly fine at idle, it is smooth and normal all the way up to about 2500rpm, thats the problem. If i had one cylinder out this whole time I would have had this figured out a long time ago. The issue i'm having is it acts fine, drives fine but once i rev it up to and around 2500rpms, it hesitates and and shakes really bad.

I cant test it the way spectre3000 has mentioned because the problem does not exist at idle, it only exists around 2500rpm. If it is an injector, its acting like it is on its way out but hasn't quite made it there yet or one of them has gotten partially clogged and it can deliver enough fuel at idle and low speed driving but under higher pressures it cant deliver the fuel required.
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I didn't quote the first comment about the old school method causing damage, but it won't. The condition would be far too short, and the damage you're causing by maintaining the situation over time is worse.

As far as giving my trick a go, you'll have to rev it up to the 2500 rpm mark manually at the throttle from the engine compartment. It'll run like it's missing a cylinder all the way up and then get worse at 2500 rpm (if not die) for every cylinder but the one that's causing the problem. That's how you HAD to do it prior to computers, even with catalytic converters. Give it a try, you've done everything else. It'll take a half hour and you'll know.

That said, I mentioned in my first response that I didn't see how you had ruled out the fuel pump; how was it ruled out? Have you tested it? It's still culpable in my book lacking evidence to the contrary.
 
Spectre6000:
I'll give your method a shot tonight if your confident its not going to do damage to anything else and it isn't still ridiculously hot out. The reason I had ruled out the fuel pump was because I replaced it with a brand new Denso pump and nothing changed.
 
I've never done it on an engine this new, but I've done it on dozens of others dozens of times. The potential damage is in the unburned fuel entering the catalytic converter creating a rich condition (like during warmup) for a very short period. The potential damage of maintaining the status quo is a lean condition in the catalytic converter which would cause it to run hotter and burn out. I'm sure it'll throw a code due to the obvious miss, but that's easy to reset with the EFI fuse when you've found your cylinder. Just be sure to let it warm up before you start (eliminate one potential variable), and shut it down while you're manipulating the spark plug wires. I said it earlier, but I'll say it again: the shock won't kill you but it won't be pleasant (you won't do it a second time). Also, be sure the unplugged cable is positioned such that it doesn't ground out to anything it shouldn't (i.e., the ECU). In fact, hold it with some rubber handled pliers and don't be a ground. You'll know quickly if you are, and again it won't kill you just be unpleasant.

Also, while you're in there just to check one other thing since you already have it apart, test the spark to the unplugged cylinder before revving it. A weak spark COULD cause these sorts of problems. It's probably not the cause, but you might as well know for absolute sure while you're in there. Before revving it up to 2500 RPM, take the plug wire that you're holding in your off hand with the rubber gripped pliers and touch it to something you know to be grounded (frame, body, block, etc. just not something with a computerized bit between where you touch and the negative pole of the battery) and make sure it's a good strong spark. Just let it spark 1-3 times; however many times it takes to SEE the spark (it'll be easier if it's dark, and it sounds like you'll be doing it at night when it's cool to boot, so that'll make it easy) but don't hold it there to erode whatever it's grounding on. It'll make itself known by being dimmer and/or a slightly different color than the other sparks. This is another of the old school diagnosis tricks; dozens of times, dozens of engines, won't hurt a thing save maybe your pride if you ground yourself with your drinking buddies watching (you're just about guaranteed to make an "EEP!" noise that your buddies will find hilarious and/or hit your head on the hood or something).
 
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I have already felt that quite enjoyable jolt from the spark plug wires and your right, it is most unpleasant. I'll start with the cylinders that are suspect based on the code that has been thrown previously and work my way from there.
 
I'm checking this thread periodically to see how it goes. If you have any questions, PM me and I'll shoot you my phone number. Please post results either way.
 
Alright, i spent an hour outside under the hood and managed to not shock myself which in its self is good news. Unfortunately that is the only good news. I removed spark from each plug and ran the engine for each plug and that yielded no significant result other than the hesitation/stutter/stupidengine problem is still there. I removed spark from each plug and started it up each time and there was no change, I also tested the spark of all the plugs since I was there (as suggested by Spectre6000) just to eliminate them, they all had good strong spark. So with that all in mind I'm inclined to think that this is not injector related unless all the injectors are clogged :shrug:

I will tell you this though, starting the engine with a missing cylinder is worrisome, but having to rev it up is all together alarming lol.
 
Haha! Yeah. If you're not used to it it can be pretty scary. I've done it with much older and more fragile engines many times though, and it doesn't hurt a thing.

So strong spark on all cylinders AND no delta from idle up past the 2500 RPM mark. Are you sure it went past 2500 RPM (i.e., someone watching the tach or an automotive multimeter set up to watch)? What did it do once past the 2500 RPM mark? Any change at all from the obvious miss on any cylinder?
 
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i had a friend observing the tach telling where when it would start doing it. Its strange cause I figured this would definitely yield some kind of result but each cylinder was fairly consistent having it happen right around 2500-3000rpm, no higher did it start and no lower.

I've been conversing with another friend of mine who's a mechanic up in alaska, he seems to think that its the MAF. I have cleaned it, using MAF cleaner from the parts store, every other time i clean my filter. It could be that but at this point its hard to say for sure.
 
You mentioned in post 23 you were going to have the shop double check the timing. Did you have that done? Sorry if I missed it.

To me it sounds like a timing issue, maybe not the belt but a sensor like the crank position sensor. Maybe you're not misfiring but firing at the wrong time. Like when spark plugs get so old they sputter and mis when slowly accelerating under 2K rpms. Also you mentioned it wouldn't start one time after driving it. I've also read about the CPS causing this but it's not common so.. just a thought.
 
MAF would throw a code, no? Same with any of the other fuel system sensors. If you're convinced this is the case, get a cheapie at your FLAPS and if it doesn't fix the problem return it (or return it anyway and get an OEM replacement).

Does it stutter when revved in neutral in the first place? I assumed it did, but the load might be a factor. If load is a factor, the test will work rolling as well (though it might be even freakier than revving it by hand).

One thing you might try is to drive it a little bit (fully in tact) and maintain the higher RPM for however long it takes to throw the code. I know it takes a while, but if you can get it to code, it could narrow it down. You have the problem then of the potential damage from the lean condition, but that's about the cheapest remaining diagnosis method I can think of and the bad cat can wait the month or so for your financial situation to open up. It sounds expensive, but it's cheaper than the several shop hours the average shop will take to diagnose something without a code these days (no one knows how to fix an engine if the computer doesn't tell them how anymore). Are these cats the stupid weld-in variety?
 
I had an appointment set up to go have it looked at but it wouldnt start so i had to cancel that. I multimetered the CPS and it read in the norm, that's not a for sure thing but but short of replacing it to see for sure, not sure how else to test that. Its possible if timing was cause it to misfire bad enough it might throw an ignition code but its hard to say. I still would like to have it looked at but I'm not sure when I'll get the chance again for a while. Its unfortunate that it decided to not start on that day
 
kball said:
You mentioned in post 23 you were going to have the shop double check the timing. Did you have that done? Sorry if I missed it.

To me it sounds like a timing issue, maybe not the belt but a sensor like the crank position sensor. Maybe you're not misfiring but firing at the wrong time. Like when spark plugs get so old they sputter and mis when slowly accelerating under 2K rpms. Also you mentioned it wouldn't start one time after driving it. I've also read about the CPS causing this but it's not common so.. just a thought.
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Overly-advanced ignition timing would cause it to run hot and would show up on the temperature gauge with no stutter and a pronounced ping. Too re****ed timing would stutter from idle to about 1500 RPM, then be sluggish once it smoothed out. Fuel economy would also be affected, and O2 sensors would throw codes. None of this has been noted.

A delta in valve timing would cause some pretty nasty stuff (anything from pinging to ignition in the runners). It would be a very obvious problem and would trip O2 sensors at the very least. Since it runs fine at lower RPM, this is not the case.
 
apparently the P1300 code that i have gotten a couple times already could be caused by a bad MAF. I found a cheap MAF on ebay that's "new" that i could use to be sure that's not it. I'm going to give that a try, if it doesnt work then i return it, if it does work, i return it and use the money to buy a quality MAF.

Last I remember when I ran it neutral the problem was present. I do know that load is a factor because when this all started hills were a problem, i couldn't push down on the pedal without it stuttering at a lower rpm going up hills.
 
T4RFool said:
apparently the P1300 code that i have gotten a couple times already could be caused by a bad MAF. I found a cheap MAF on ebay that's "new" that i could use to be sure that's not it. I'm going to give that a try, if it doesnt work then i return it, if it does work, i return it and use the money to buy a quality MAF.

Last I remember when I ran it neutral the problem was present. I do know that load is a factor because when this all started hills were a problem, i couldn't push down on the pedal without it stuttering at a lower rpm going up hills.
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yeah sounds like the MAF as well, i thought you already ruled that out at one point though? that would have been one of the first things i would have suggested otherwise as i was having this same issue, i just got lucky that i had 2 spare 4runners laying around so i could swap some maf's around to see if that was the problem.

that was the first thing i checked and it fixed my problem, i have a steep driveway and the truck would want to stall trying to back out in the mornings and kept throwing the p017xx code (run lean)

hope this fixes your problem man!
 
I ruled it out because I tested it with a multimeter which showed it was working fine and I ran the truck with it plugged in and without it just to be sure and it ran way better with it plugged in. But as a friend of mine has informed me those aren't for sure ways to test a MAF. Apparently you have to hook it up to some machine and blow air through it while monitoring the read outs blah blah lol. So I bought a cheap MAF to be for absolute sure. If it turns out has been the cause the whole time I might just go bang my head on a rock cause it is one of the first thing that I looked at lol
 
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