Car bucks/jerks going onto throttle, coming off throttle, and holding part throttle after warmup?

92GS603 · Aug 15, 2014

Let me just say that I've had this issue for a long time now, but it's become such an annoyance that almost 2 years after it started, I'm finally sick of it and seeking answers. Title says it all--If I quickly go onto or off of the throttle, or hold the throttle between 0-15% (guessing, but basically just enough to hold a steady speed), the car bucks. It does it in every gear, and is most pronounced when slamming the gas pedal to accelerate hard. It starts out during early warmup with a delay (let off throttle, then bucks after a 1-2 second delay). There is also an occasional instance of rough idle, but its fairly rare.

Since it started, the following parts have been replaced due to failure or out-of-range operation.
-MAF (IAT sensor was way off) --didn't help bucking at all
-IACV (flat-out died) --didn't help bucking at all
-Coolant temp sensor (was reading way off) --moderately reduced the severity of bucking
-Plugs and wires 2 times (20k miles, first set of wires rubbed on other parts til they started arcing) --little to no change
-O2 sensor (old one was dead) --little to no change

I have also replaced the PCV with a new OEM one, and have replaced the fuel filter and ran BG44k through twice. I have not had a chance to check the fuel pressure, but the fact that the bucking is delayed during the early warmup period makes me believe it's a sensor and also rules out it being drivetrain/transmission lash.

As for the other things I've tested, here is what I got:

TPS: 600-5000 ohms from 0%-100%, no weird spikes or dips but the low bottom end makes me suspicious, as it's supposed to be ~1100-5500.
With the harness attached it's putting out .48v at closed which is within the range that the Haynes says it should be, though I'm very tempted to adjust it up above .50v just to be safe.

Coil Pack: Primary resistance is around .9-1.0 ohms when cold and just slightly higher when hot. Secondary for both coil sets is around 13k cold and 15.5k hot. Seems slightly out of range.

Closed throttle switch: Operating properly

Vacuum system: No leaks that I can find, idle is VERY smooth for a DSM.

I have yet to check the CAS or power transistor, but my understanding is that either of these going bad usually causes you to lose 2 cylinders. Keep in mind that this is also a non-turbo daily driver, so I don't have any A/F gauges or access to tuning software to let me see all of my sensor values on the fly.

bmxfelon420 · Aug 15, 2014

Hmm there are a few things I can think of that may cause that sort of issue.

What plugs are you using and what are they gapped to? Turbo cars at least dont like plugs that arent NGK's
Have you checked your injectors? They may be dirty. Fuel filter is another thing to check.
I'd also look into what the exact TPS voltage is supposed to be as per FACTORY service manual. I dont trust haynes with specs like that.

Another real easy thing to do is pull the cover off of the ecus. Any blown caps or discoloration would mean it needs repaired. If you dont know that it has already been repaired very recently, it's very likely. Capacitors dont like to last for 20 years in cars.

92GS603 · Aug 15, 2014

I've been using NGK BPR6ES's gapped at .44, like NGK suggests. Fuel filter was replaced about a year ago and only has about 10k miles on it, all with Shell gas.

As for injectors, I was planning to clean them if I decided to adjust the TPS since I have to pull the rail off to do that anyways. Would be doing seals as well.

I know the ECU was replaced by the previous owner sometime during 2011, but I'll check that out and see if it looks like a junkyard part (yellow writing on the exterior and whatnot).

bmxfelon420 · Aug 16, 2014

Alright, yeah even my 95 ECU needed all the caps replaced.

92GS603 · Aug 16, 2014

bmxfelon420 said:
Alright, yeah even my 95 ECU needed all the caps replaced.

Well I checked the old ECU (which had TONS of cap leak damage) and matched its part number to the one currently in there (MD166255), and also found that the 5 speed and automatic share the same ECU, so no question of it possibly being the wrong one or something like that. I've got the next 2 days off so I'm gonna fully pull the current one out and check it for damage, and also going to check injector resistance since I haven't yet.

luv2rallye · Aug 16, 2014

I would say dirty injectors are the prime suspect.

For NT, spark plugs should be NGK BPR6ES-11 and gapped in .048-.053" range.
Spark plug diagnosis:
http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp or
http://www.gnttype.org/techarea/engine/plugs.html.

NT TPS between pins 1-3 should be constant in 3.5k-6.5k ohm range (this is the max value). Between 2 and "1 or 3" it changes with position and direction: <100 to max or max to <100 ohms.

Another possibility is a weak coil: Remove plugs and reconnect with casings clamped to engine, then crank and watch spark to see how strong a spark you have (even this isn't a sure test but if the spark is weak you know it's bad). Coils get weak with age. Often heating them with a hairdryer/heatgun while testing will help bring out a weak/bad coil.

92GS603 · Aug 16, 2014

luv2rallye said:
I would say dirty injectors are the prime suspect.

For NT, spark plugs should be NGK BPR6ES-11 and gapped in .048-.053" range.
Spark plug diagnosis:
http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp or
http://www.gnttype.org/techarea/engine/plugs.html.

NT TPS between pins 1-3 should be constant in 3.5k-6.5k ohm range (this is the max value). Between 2 and "1 or 3" it changes with position and direction: <100 to max or max to <100 ohms.

Another possibility is a weak coil: Remove plugs and reconnect with casings clamped to engine, then crank and watch spark to see how strong a spark you have (even this isn't a sure test but if the spark is weak you know it's bad). Coils get weak with age. Often heating them with a hairdryer/heatgun while testing will help bring out a weak/bad coil.

Just out of curiosity, where'd you get the .048-.053 specs from? NGK's site said .044 for n/t 4g63's last time I checked.[DOUBLEPOST=1408252098][/DOUBLEPOST]Nevermind, just realized that's what the factory manual states. Which source should I be following?

luv2rallye · Aug 17, 2014

Factory manual.

92GS603 · Aug 17, 2014

-11's are the ones I've been using--was just abreviating, haha. I'll definitely be throwing in some properly gapped new ones tomorrow, though. I'm gonna feel like such an idiot if this tiny error has been doing this all along.

luv2rallye · Aug 17, 2014

I doubt that little gap difference is your problem.
Not that it should make any difference but in my 99 Eclipse owners manual it lists Champion RC9YC5 as the recommended plug for the 420A NT. I can't imagine why NGK shouldn't work though.

wolf alchemy · Aug 17, 2014

I've always wondered why our cars love NGK plugs....I know its a question that's not really right at home, but eh. I wanna chat[DOUBLEPOST=1408262807][/DOUBLEPOST]Plus that should have been my 30th post. =D Or this is....

92GS603 · Aug 17, 2014

Well here's something strange...my catalyst sticker under the hood says the gap should be .039-.043, and not .048-.053 like the manual allegedly says.

I also found the box for this set of plugs learned they are actually just plain bpr6es's despite me asking the guy at the parts store for 11's...guess I should probably check the package next time, LOL

.

EDIT:

Found a pdf for the factory service manual at http://www.scribd.com/doc/15602877/dtm

They state .039-.043 as well, so I have no idea now where the .048-.053 is coming from.[DOUBLEPOST=1408304293][/DOUBLEPOST]Well, opened up the ECU. Doesn't immediately look like there's and damage to the board like the old ECU has, but the capacitors look much different and like they've been replaced at some point. There's also an abundance of what looks like dried glue all over the place, and the board as a whole is much less "shiny" than the old one.

Let me know if you guys have any input or see anything wrong or noteable that I missed, as I'm a nub with this stuff

You must be logged in to view this image or video.

luv2rallye · Aug 17, 2014

92GS603 said:
Well here's something strange...my catalyst sticker under the hood says the gap should be .039-.043, and not .048-.053 like the manual allegedly says.

I also found the box for this set of plugs learned they are actually just plain bpr6es's despite me asking the guy at the parts store for 11's...guess I should probably check the package next time, .

Found a pdf for the factory service manual at http://www.scribd.com/doc/15602877/dtm

They state .039-.043 as well, so I have no idea now where the .048-.053 is coming from.

Your link which states .039-.043 is for a 1g NT which uses a Mitubishi engine. The 2g NT engine is made by Chyrsler (420A) and states .048-.053 on page 00-40 here: http://www.scribd.com/doc/17887620/97-99ECB. Of course those with a 6 bolt swap will have the Mitsu engine so the gap will be for it (notice the turbo vs NT have different gaps however even for the 1g).

As far as the BPR6ES-11, the -11 is the gap designator (see: http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf), so you can either get them to have the gap preset (NGK sets to .044 in this case), or get the BPR6ES and gap them yourself to whatever you like.

A couple of Tuners tidbits on NGK plugs:
http://www.dsmtuners.com/threads/which-spark-plugs-to-get.72181/
http://www.dsmtuners.com/threads/spark-plugs.198308/page-15#post-1642842

92GS603 · Aug 17, 2014

luv2rallye said:
Your link which states .039-.043 is for a 1g NT which uses a Mitubishi engine. The 2g NT engine is made by Chyrsler (420A) and states .048-.053 on page 00-40 here: http://www.scribd.com/doc/17887620/97-99ECB. Of course those with a 6 bolt swap will have the Mitsu engine so the gap will be for it (notice the turbo vs NT have different gaps however even for the 1g).

As far as the BPR6ES-11, the -11 is the gap designator (see: http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf), so you can either get them to have the gap preset (NGK sets to .044 in this case), or get the BPR6ES and gap them yourself to whatever you like.

I have a 1G Eclipse GS, which has a N/T 4G63.

luv2rallye · Aug 17, 2014

Well there ya go. With this new site we never know what year/model a poster has unless he states it so assumptions get made. I thought you had a 2gNT.

92GS603 · Aug 17, 2014

No harm done! I'm used to seeing that information as well, which is why I didn't post the car info in the OP.[DOUBLEPOST=1408324287][/DOUBLEPOST]Okay, possibly big update! Went out and listened to the car idle after spraying my plug wires to check for leaks and noticed something I never have before. Every time I get an engine miss at idle my, #3 injector makes a very pronounced tap/click sound that you can hear over everything else. It's perfectly consistent with every little hiccup in the idle, and it was hiccuping A LOT after everything got wet.

92GS603 · Aug 20, 2014

Gapping some new plugs down to .41 helped a little bit, but it's definitely still there. I'm replacing plug wires tomorrow since mine are arcing again, but the plugs in there once again looked completely normal--if anything just with a little bit more white deposits on the ground electrode than a perfectly healthy engine would produce.

Question--is it possible that if my injectors were partially clogged, the problem would be less apparent during warm-up because the open loop operation is inherently dumping extra fuel into the system, making it easier for more fuel to get past the blockage and into the cylinders?

luv2rallye · Aug 20, 2014

Possible. Clean those injectors: http://www.dsmtuners.com/threads/cold-weather-engine-issues.448803/#post-153136134.

92GS603 · Aug 25, 2014

Well, new wires are in as the old ones were arcing. Engine runs a bit smoother now, and the I have yet to experience the part-throttle miss/bucking since the new plugs were put in. Bucking on and off the throttle is still there though.

Since I noticed I left it out while rereading my posts, I guess I should mention that I can avoid the bucking if I VERY slowly and gently get on and off the throttle.

So I'm still wondering (as its the only sensor that seems off) if my TPS might be causing this, as I'd like to be able to make sure whether or not it's good before I go ahead and pull the fuel rail off. I'd rather not have to pull it off twice if the TPS ends up being the issue and not one of the injectors.

As I said earlier, the stated range in the repair manuals says the TPS should read:

1100-5600 ohms between pins 2+4 from closed to open (I'm getting 600-5000)
3.5k-5.6k ohms between pins 1+4 (I'm getting 5k, in range)
.48v-.52v output at closed throttle (I'm getting .48, but multimeter occasionally jumps down to .47 for a second or so)[DOUBLEPOST=1409078100][/DOUBLEPOST]Adjusted the TPS to .50v. Bucking is still there, but it's not as harsh as it was before. It was actually reading .47v today before I did it, which is out of range. Resistance is still reading much lower than the manual suggests, so some input on whether or not that could still be affecting this would be great. In the meantime, guess it's time to order new injector seals

92GS603 · Aug 28, 2014

Adjusted the closed throttle switch today and the intensity of the bucking when coming OFF the throttle dropped dramatically. Idle smoothed out as well since it was holding the throttle plate slightly open before. Jerk/buck when slamming the throttle is still just as bad as before, though. In fact, unplugging the switch doesn't seem to make any difference in the way the car drives, despite it appearing to work properly and the green wirethat goes to it having 12 volts. My understanding is that unplugging it should actually cause a condition of no rolling fuel cut.

92GS603 · Sep 2, 2014

Well, I think I found it...went back out today to double check that all of the sensors were getting proper connection to the ECU and found this while checking the O2...

You must be logged in to view this image or video.

Ground circuit on pin 2 was reading something like 58.4 on the 20,000 ohm setting, and it would lose continuity from moving it around wrong, so I guess it's safe to say the O2 sensor hasn't been doing much of anything this whole time (no wonder replacing the dead oem one didn't do anything).

What are my options here? I wrapped that break with some electrical tape, but who knows how long it will last and if it will change anything.

MasterFrmMO88 · Sep 2, 2014

It's difficult for me to tell from the picture but is there a clean break there or just an exposed wire? If its just an exposed wire then electrical tape won't do a whole lot. With the signal losing continuity if you move it wrong, that tells me there is a clean break somewhere along the wire. Look in areas where it might be exposed to excessive heat. May be just me but if I run into these problems, I usually just cut and isolate the bad wire then run a new one in a safer route.

92GS603 · Sep 2, 2014

I fiddled with it some more and can't get it to lose continuity (probably just bad connection on the plug when I was doing it), but the resistance of that wire is still absolutely massive. Not sure whether or not the high resistance matters much as long as there's continuity, but since the sensor plays with voltages less than 1 volt I imagine any inconsistency in the wiring would probably mess with it.

The copper definitely doesn't look like it's damaged inside, but the insulation looks much thicker than on a lot of wiring I've worked with in the past, presumably to better help fight off heat soak from sitting right next to the radiating engine block? I imagine electrical tape probably does very little in the ways of insulating against heat, which is why there was virtually no difference in the way it ran after taping it.[DOUBLEPOST=1409766813][/DOUBLEPOST]I don't have my exhaust ground strap hooked up, and I've heard (unconfirmed) that it can help provide a better ground for the O2 sensor. Since the damaged wire is a ground, is there any chance that hooking it back up might help?

92GS603 · Sep 11, 2014

Well, I went back and checked over everything again. I tried testing my ISC using the key on-off method and it didn't move despite it ohming out properly. Replaced it with another known tested good one and it did the same thing. The original ISC the car had when I bought it stopped working due to a dead coil, so I'm guessing my ECU ISC driver is dead or damaged. The car idles pretty flat, but it likes to dip low and run rough when the cooling fans come on, and also likes to do it sometimes when coming to stop signs. Unplugging the ISC makes no difference in driveability.

The VFAQ also mentions that the ISC is supposed to be open during driving so that letting off the throttle doesn't cause the car to buck, which is why I started searching this route. I'm going to get another ECU and check back after I've tested the car with it.[DOUBLEPOST=1410492195][/DOUBLEPOST]Never mind, went and tested them again before biting the bullet and dropping >$100 on another ECU and now they both work.

92GS603 · Feb 4, 2015

5 months later and I'm still stumped on this. I replaced the ISC shortly after my last post with no change, and just installed and adjusted another TPS and replaced the throttle body gasket, ruling out yet another vacuum leak spot. I blocked off the EGR last month, eliminating the possibility of the emissions lines causing leaks as well. Engine still pulls perfect on acceleration, but the car still has issues near the throttle open/close threshold. Sometimes the bucking gets so severe, while holding the throttle barely open, that I swear I can hear a high-rate misfire for split seconds at a time, yet no CEL ever pops up. All the while, I'm still maintaining 30+ MPG mixing highway and normal streets.

Remaining list of things this could possibly be, based solely off of replacing parts and knowing how minuscule the possibility that parts were replaced with similarly malfunctioned parts:

-Coil pack? (possibly worn out, or overheating from the insulating paste no longer efficiently working)
-Injectors?
-ECU?

Any other ideas?

The Top DSM Community on the Web

Car bucks/jerks going onto throttle, coming off throttle, and holding part throttle after warmup?

92GS603

bmxfelon420

92GS603

bmxfelon420

92GS603

luv2rallye

92GS603

luv2rallye

92GS603

luv2rallye

wolf alchemy

92GS603

luv2rallye

92GS603

luv2rallye

92GS603

92GS603

luv2rallye

92GS603

92GS603

92GS603

MasterFrmMO88

92GS603

92GS603

92GS603

Similar threads

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds