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Author Topic: seemingly random bogging at low rpm, high throttle (mk1)  (Read 1695 times)

Offline SC S12

Been a long time since I posted.
I am once again asking for your support...

As stated I have a strange random loss of power, specifically in the 2000 to 3400 or so range. Sometimes it just falls on its face to the point of full throttle barely making it accelerate any faster.

But its not all the time, nor is it closed/ open loop Dependant.

Things ive checked : fuel system. New pump/check valve (ecu said it had a fault) new fuel filter. After warmed up fuel line pressure is a steady 37 or so psi, which jives with the manual. Keeps around 25psi in line when cut off with no leakdown.

Rotor checks out as fine via multimeter. Cap checks out as good via multimeter. Wires are about 3yr old, coils are about 2yr old, and still work independent, I never bridged the exhaust to the intake side. Pulled a few plugs randomly and they look good as well, no buildups. Ordered new rotors in case, have a stock pile of caps.

O2 sensor is relatively new, and reads out correctly (around .565v at idle with some light bouncing, nothing major)

Things I replaced and am not sure about : all vacuum lines were replaced about 3 months ago. I did not keep the filter/flow reducer sections that go from the throttle body to the TVV. Could this be causing it to suck too much advance and stumble? I had to drop the idle like 200rpm after removing these sections. Else it would idle around 1000 when you hoocked the vac line back to the dizzy.

Things I'm not sure on, haven't touched :
Chts : replaced when I got the car like 5 years ago, but seems fine.
Tvv : replaced a few years ago, did not ever let the vac advance work. New one never seems to kill the vac advance in my current testing(almost like its stuck open) ordered a new one, have yet to install.

Considered bad fuel, but it has persisted across a few fill ups of varying grades.

Another oddity : the exhaust side coil never stops firing. On my mk1.5 it cuts out at 4000 rpm or so. I drove the mk1 I'm messing with on both, e only, and I only coils all the way to redline without issue. Seems odd. Book says that they both fire any time chts says 59f or less, but other temperature related things are working (fuel injector cut off)

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Offline kelso840

Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #1 on: 02:16:24 PM / 11-Mar-20 »
Try swapping the lead wires between ignition and exhaust coils and see if you notice any change. Also check to make sure there's no corrosion building up on the ground wires coming off the coils.

I haven't had a CA for a long time but the coils always seemed to be a source of funny business.
Infrequently driving an s12.

Offline BOSSMAN

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Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #2 on: 02:44:03 PM / 11-Mar-20 »
I had similar issues with bogging at high rpm with my turbo.  One time was a cut with my primary coil wire to cap, wires were three months old at that time, on the second time it was reversed primary plug wires between cylinder 1 and 2 after I put new plugs in.  Like you said the secondary coil should stop work when the engine go pass 4000 rpm under heavy load so in both cases there was a problem with my primary ignition side when my secondary side stops working.  One member I helped out a long time ago with bogging turned out to be his newer fuel pressure regulator he just installed.  I'm not sure how the NA pressure regulator works but for the turbo under boost (no vacuum) the regulator will open to let more fuel in but the guy put a regulator from a CA18det and that one works in reverse.  The newer regulators are place in the outlet side of the fuel rail controlling the flow going out whereas our older cars have the regulator in the inlet side of the rail controlling the flow going in.

Post Merge
PS: see kelso840's reply and double check all the ignition wiring.
« Last Edit: 02:46:30 PM / 11-Mar-20 by BOSSMAN »
86 CA18ET....owner since 1990.
The name is Bossman, but you can call me Mr. Panda....My other car is a Buick....
My Skyline is here!  My Skyline is here!

Offline SC S12

Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #3 on: 11:01:55 PM / 11-Mar-20 »
some update with a mostly fixed issue:

on a whim, I kept all the old vac lines i took off in the past.
spliced the flow restrictors from the two manifold vacuum lines into my new lines. Re-adjusted idle again and re-timed for the new idle speed.

As it turns out, at least on this car, If you dont have those flow restrictions in feed lines for the TVV, when you set the based time to 4* BTDC, when you hook the vacuum line back to the dizzy your idle time is around 22*btdc, Any slight blip of the throttle makes the timing marks totally vanish from sight like it just maxes out the vacuum advance instantly. Though it never sounded like it, i suppose it was misfiring or pinging like hell when was getting no throttle response.

with those back in the loop, after you set the base time to 4*btdc and hook it back up to the dizzy you are sitting around 14-15 BTDC. I still have a small miss or stumble here or there but nothing like it was.

Gonna just do the standard coil/rotor/wires/plugs and a Italian tune up and see where it falls after the weekend.

need to get this turd ready for radwood
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Offline SC S12

Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #4 on: 07:12:35 AM / 01-Aug-20 »
New updates.

Did Timing Belt and water pump+thermostat (stock temp), front main, and front cam seals, plugs +wires + dizzy cap and rotor like 2 months back.

Drove the car roughly 1k miles since, And it was doing great. Too good honestly. 28MPG first tank with AC on. Tanks on this last Trip where 27 (73MPH) and 36MPG return (67mph)

At the end of a 450 mile road trip where it functioned perfectly, it started doing this crap again about 3 miles from my house so badly that foot to the floor in 3rd gear it would slow down.


Engine takes FOREVER to warm up (like 15 minutes idle) It only reaches 1 bar into the operating range. Suspect timing is just too far advanced. I don't suspect that its a thermostat as its a new one.

Very low/rough idle when cold. Sometimes nearly stalls when clutching coming to a stop. Ocassional misfire at 40-50MPG in high gear at moderate acceleration. Cannot hear if its pinging.

Base Timing checks out perfectly at 4-5* BTDC. HOWEVER Vacuum advance at idle is about 22* again, instead of 14-16*. The lightest blip of the throttle pushes the advance i'm Guessing all the way to max (maybe 40* ?)

Will replace TVV and Update later today.
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Offline weitrhino

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Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #5 on: 02:41:42 PM / 01-Aug-20 »
Pulled any ECU codes?

Offline SC S12

Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #6 on: 07:42:00 PM / 07-Aug-20 »
Pulled any ECU codes?
Only one is the fuel pump (wrong sending unit so it always is in the current/history and my fuel gauge does not work properly, but the pump itself is a new JECS unit)

I replaced the TVV and it helped out a lot, especially in the low end and just off idle. No More stalling Coming to a stop.

I just barely touched the nipples and the whole top of the TVV shot off like a rocket. I'm Not sure why this thing failed, it was only 2-3 years old. Found all the springs and valves and it looks like it was dragging on the little pin too hard on one side, And I guess was stuck or the housing was cracked.

After Thinking about it, I just replaced the Primary and secondary coils and that seemed to fix the high end breakup. They were both about 1000Ohm too High on the secondary circuit.

Its back to running well, and running at temp for now. It seems odd that id have two failures at the same time, but... who knows.
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Offline weitrhino

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Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #7 on: 09:55:03 PM / 10-Aug-20 »
Good diagnosing. With a 35 year old car I've tried to stop thinking in terms of a single problem - single fix. It's not always so easy though.

Offline SC S12

Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #8 on: 10:39:42 PM / 08-Jun-21 »
Bumping again on this.

Misfire at idle is still there, but not under load. Just got done with a really extensive tune up fixing EVERYTHING the voltage spikes killed.
the slightest load ( turning on parking lamps) will for the most part entirely remove the random idle misfires.

it will pur at idle but randomly you just get hmmmmmmmmmmpfthmmmmmmm sort of transient misfire.

for

Replaced Items :
1. Plugs -gapped at .0475 (for reasons)
2. Wires
3. New Coils ( accel Super Sports. .6ohm/11.2k ohm, 45kv)
4. new Fuel Pump ( original was leaking at the wire pass throughs)
5. new injectors ( a few were Ohming out when hot causing stumbling, subie sounds complete with full crackles)
6. cap and rotor with Brass contact versions
7. Extra Motor/efi harness grounding
8. Alternator ( rectifier Failure)
9. Fusable Link

Verified:
1. TVV is functioning properly
2. Repaired vacuum lines to egr/BPT/fuel throttle up solenoid. ( bottom feed to BPT was fully torn)
3. EGR is functioning and moving properly.
4. Idle Up solenoid seems to be working properly
5. Cold start/fast idle valve is not really working, but also not leaking air into the intake either. Failed Closed. (shouldn't Matter)
6. ECU has no Error codes most of the time(44). Neutral switch occasionally stops working, but does not seem to impact the misfires
7. Throttle Switch is correctly set and working, as is dashpot.
8. Idle Mix according to ECU is okay ( both LEDs blink in unison)
9. Base time at 4btdc, Vac time when hot 15BTDC
10. Fuel Pressure at idle is 30PSI, Pressure at WOT load is 37psi

Yet to Verify :
1. Cam Timing Jumping a tooth? (unlikely)
2. o2 Sensor reads .55-.58 Volts at idle, seems a little rich and I'd expect .48-.52 or so.
3. CHTS functionality ( though it is new as of 3 years ago)
4. MAF not checked, but seems to be working.
5. Minor leak Between Cast Header and the Y portion of the downpipe.
6. Possible bad fuel ( cut with water?) due to the artificial fuel shortage a few weeks back. I have not actually tested it though.


Sort of stalled out of ideas on things that could be causing this.




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Offline rednucleus

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Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #9 on: 11:35:04 PM / 08-Jun-21 »
The thing that helped my random misfires the most was to pull the ECU board and touch all the solder joints with a hot fine solder iron. I found I could push/wiggle some components, especially capacitors, worsening the misfires. Has been as close to perrfect now since that repair a few years ago now.

Offline SC S12

Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #10 on: 11:01:49 PM / 09-Jun-21 »
The thing that helped my random misfires the most was to pull the ECU board and touch all the solder joints with a hot fine solder iron. I found I could push/wiggle some components, especially capacitors, worsening the misfires. Has been as close to perrfect now since that repair a few years ago now.
I'll check that in the coming days. I don't have a spare black top ECU in case I bugger it up.

More troubleshooting.
1. CHTS reads out correctly ( ~300ohm) once warmed up to operating temp ~ 175-180 F indicated by my gauges, as measured at the ECU connector.
Cam has not jumped a tooth.

2. Cleaned the heck out of the throttle body and the two hard nipples that feed the TVV at the throttle body. a ton of sooty junk was dislodged from them.

3. I am unaware how it works with the black tops, but the MAF seems to be working. Press on the vane and idle does change, even if the throttle plates not moving( flood out I guess). Will not run with MAF unplugged unlike my silver top car ?

4. Odd sucking sound from the idle adjust valve and its piping area. I've not ruled out a leak here. pinching it off by the battery stops the sucking sound, but of course also kills the engine. Is the idle speed valve really noisy normally?

5. Went through entire diagnostic procedure and all sensors report to the ECU. fuel mix at 2000 RPM is spot on. Fuel mix at idle is sometimes good, some times not. When its not, only the green lamp is blinking, or it blinks, with the red lamp trailing a second or two behind.

6. Misfires are worse the hotter the car gets, which to me makes me think leaning out as it warms up. either a vac leak, or a leaking/sticking control valve somewhere.

7. Misfire is random, in duration, and frequency. Sometimes its dozens in a span of a few seconds. Others it might idle 20 seconds between "puffs". I think this rules out a hung/burnt valve as that would be consistent.

8. Checked Oil for water/ Coolant for oil. I can't see any contamination. I don't blow smoke out the tail at idle, or load, of any color.

9. re-verified spark : both intake and exhaust plugs will spit a blue-white ark across an airgap ~2-3 inches to the closest ground. I get no spark cross talk through the rotor/cap ( something that's caused bad idles for me in the past)
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Offline rednucleus

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Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #11 on: 11:30:51 PM / 09-Jun-21 »
Have you ever changed the module in the distributer? You mention it worsens as it gets hot; that module may start acting up when hot. I think rockauto has them on closeout.
« Last Edit: 11:31:16 PM / 09-Jun-21 by rednucleus »

Offline SC S12

Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #12 on: 11:39:44 PM / 09-Jun-21 »
I have not, but did order one as they were only 50 bucks on rock auto, and a new reluctor  since those are only 5 bucks and it has to come off anyway.
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Offline weitrhino

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Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #13 on: 06:33:12 PM / 10-Jun-21 »
You might be wise to check the coolant temp sensor, the one under the 3" rubber intake hose at the intake manifold. A poor connection there could cause the ECU to alternately think "hot engine" or "cold engine" and futz with your fuel/air ratio. Those old EV1 connectors get brittle with age and are easy to replace.

Offline SC S12

Re: seemingly random bogging at low rpm, high throttle (mk1)
« Reply #14 on: 08:39:40 AM / 11-Jun-21 »
You might be wise to check the coolant temp sensor, the one under the 3" rubber intake hose at the intake manifold. A poor connection there could cause the ECU to alternately think "hot engine" or "cold engine" and futz with your fuel/air ratio. Those old EV1 connectors get brittle with age and are easy to replace.
I actually checked it back at the ECU pins since that is easier to do, it checks out fine @ 70f to & 180f or so. I think this is good, and really want to minimize taking the temp sensor connector off as its brittle as can be.

Have you ever changed the module in the distributer? You mention it worsens as it gets hot; that module may start acting up when hot. I think rockauto has them on closeout.
I hooked my oscope up to the intake (red?) and exhaust trigger (blue/white) wires from the ICM with the car running. Granted this is through the insulation.
its the UGLIEST waveform I've ever seen with a ton of noise and flapping around between the spike, sometimes it pulls a massive negative spike too, and never even getting to 4volts out.

As the engine gets hotter, this becomes more erratic, and occasionally either compresses going from 290hz or so to into the thousands of hertz( but with much smaller spikes) or totally blanks out dropping for a fraction of a cycle. ( might not be hitting my sense trigger voltage)

Something does seem to be screwy here.
Post Merge
Misfire Solved.

1. ICM was not tightly secured. Ground had no continuity according to a multimeter. Pressing on the ICM or the screw that holds it in would fix that. Removing the screws, scuffing them up really well and putting a small bit of copper antiseize on them and running them in and out a few times fixed the continuity issues. Really cleaned up the waveform on the oscope too. Cruising at 60 is smoother now too, with a lot less vibration and less noise.

2. Valve lash was too tight across the board. Found On a whim by testing with the dollar bill/paper trick at the tail pipe and slomo filmed on my phone.   after the above fix I was still getting random idle misfires, but they were spaced apart much further and rather than a popcorn-ish sound, it would just be a PFT sound like a dead cylinder. It was back drafting exhaust through the valves on 2 and 4. Loosening the lash to .013" instead of the stock .3mm removed the issue. Here's to hoping I did not burn them up. Its been over a year since I did the lash, Maybe it was not fully warmed up when I did it.

Car warms up significantly faster now, and reaches proper 187* or so in steady cruising, reaching up to 200 during extended idle where the E fan kicks on like its supposed to. No more wasted fuel smell either. So what I learned from all this is I am still an idiot.
« Last Edit: 09:13:17 PM / 11-Jun-21 by SC S12 »
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