combatcarl

Ok. This ain't a cry for help. More of a slow elimination of what isn't wrong. If you've got ideas, chime in, otherwise I'll leave updates, hopefully until it's fixed.

A few weeks ago, headed up freeway on ramp, third gear, pulling at 2.5-3k rpm, and get a single buck, no backfire, little cloud of smoke, and continued on with no issues. Like a switch, on/off/on, 'bout as fast as you can say "pop".
A week ago, same place, same scenario, same thing. Just one snort, and on down the road.
Yesterday, on the way to work, (driving like a meathead) pulling hard in third about 2.5k rpm, bucks n snorts several times in rapid succession, not violently, but definitely there. Slow down a little, second, pull hard, (seeing if I can replicate it in different gear) and bucks a little, then winds up clean, to 4k, shift, and no weirdness.
-no CEL
-no stored codes
-TPS shows no dead spots in sweep range
-truck is warm, but gauge not quite always in warm range when it occurs
-no vacuum leaks, perfect vacuum at all rpm
-TB needs cleaning
-injectors could be serviced, for sure
-plugs are relatively new, may replace, cheap
-dist. cap, rotor, & wires are about aged out

I need to set/check TPS, it ohms smoothly, but not quite in spec. Intermittent throttle sticking, idles up until you bump pedal, then drops down. Time for thermostat, coolant flush. One other thing, the clutch is getting old, but usually slipping clutch is a little different feeling. Still pulls hills in 5th/4th fine. So, I'll be updating as I eliminate or fix issues.

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combatcarl

Ok, so through testing and retesting, have established that TPS is within spec, and that it's working, as idle drops when check plug is jumpered. Still a little suspicious of it. Hopefully today ill order/pick up cap, rotor and wires. May do TB cleaning today as well.

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combatcarl

So to eliminate the easy fixes, I replaced plugs, wires, cap, and rotor. It's better, but I still felt a slight stumble when under hard throttle up the uphill on ramp where I noticed it first. Rechecked TPS, it's good. Timing dead on at 5* BTDC, check connector jumpered. Dead on 8* removed, advances and retards smoothly with decel/accel. Here's the plugs, look ok to me, anybody think different? iPhone only gets so close with pictures.
All:

No 1:

No 2:

No 3:

No 4:

So tomorrow, if I get up early enough before work, I'll check out the VAFM per 4crawler's write up, and maybe give it a couple hard throttle pulls, and see if it's still there.

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combatcarl

Didn't get up early, no checks on anything. Stumbled n snorted when still cold at about 2.5k rpm, third gear, under half throttle. Didn't seem to do it warmed up. So this weekend, (wed-fri) I'll be checking more stuff, and probably removing and cleaning the TB and maybe even upper intake, given enough good weather and time.

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osv

you replaced the plugs, since they were already out, correct? they all look like they are firing, fwiw.

so many things can be wrong here, it's difficult to know where to start, but i wouldn't tear apart the intake right off the bat.

maybe replace the old cap/wires/plugs first, they need it and it's simple.

also check for vacuum leaks, check egr operation.

Gevo

I am paranoid about any of the vacuum lines being bad and causing difficult to resolve issues... I haven't even really driven my 4runner anywhere, but I went ahead and ordered an air/vacuum hose kit to prevent any problems from the vacuum hoses. I would suggest changing all of yours as well. It's relatively cheap, $50. A user here pointed to lcengineering which I used. But you said your vacuum pressure checks out, so..

Reaidng through the thread, I didn't see anywhere where you considered the fuel filter. A starvation of fuel can cause this symptom. Although you may have good fuel pressure, the high rate of flow required all of a sudden may be restricted somewhere. Seems you got the spark end of things covered.

I'm not entirely familiar with the EGR and related emissions system, but if a malfunction in this system can cause performance issues, that sucks.. adds a whole system of pipes, sensors and vacuum gauge/valves to deal with.

combatcarl

Fuel filter isn't a big consideration. Was replaced four years back, with long block swap. Was in the tank a year later, no rust, very low appearance of sediment. I'll poke in that direction though if nothing else pops up. I'm thinking FPR, VAFM, or distributor. Time to do a valve check anyhow, too.

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combatcarl

To clarify, I'm not ruling out the fuel supply system at this point. Just need to do a fuel pressure test before picking it apart. The reason I'm not too worried about fueling is that it starts. Every time, just a bump of the key hot, and maybe 2-3 crank revolutions cold. Y'know, you hear maybe three cylinders roll over TDC and then it's running. Even before plugs, wires, cap and rotor replacement. I've got a little time coming this weekend, I'll poke everything and see what my meter says. Everything is original, fuel pump, lines, FPR, VAFM, TPS, EGR, coil, distributor, etc. I've got the black tar goop in the intake, which, if it's plugging off a port somewhere, could partly cause some issues.

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Gevo

combatcarl, as I mentioned earlier, a 'fuel pressure' test may not fully show that proper volume of fuel is being delivered. Unless you do an open system fuel pressure test which I've never seen on a car but that would be conclusive!

combatcarl

Yeah, there's no way I have the stuff required for that. I'm pretty sure I can sort it out with the basics, and maybe a fuel pressure measurement. Just a bit of troubleshooting to do.

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1%_Spawn

It sounds electrical to me with the stumble being intermittant, in a specific RPM range and not happening when its warmed up. I bought an 86' runner with a reman'd engine that had a stumble. The previously owner had the long block replaced, but bolted on the old components. It ended up being the 26 year old coil that caused the stumble.

combatcarl

Well, everything checks out on the ignition component side of things.
Coil is good, primary and secondary.
Signal generator is good, but rotor clearance is a little tight.
AFM checks out fine.
TPS rechecked and good.
No intake tract leaks.
So next I'll futz with the EGR side of things, then the fuel supply/pressure side of things.
Things I noticed-
Lots of black goo in intake
Distributor is about maxed out for advance, but shows dead on 5* jumpered at warm idle
Truck has been running a little warmer lately, radiator level was down just below top of tubes
Dipstick is fitting pretty loosely in tube now.
Today, stumbled and snorted getting on freeway. It takes less provocation to make it do it, but it's still a little random. No codes. Running at freeway speed, 5th gear, step into the throttle, and I can hear it rattle/ping. Sounds like marbles in a can being shaken. But no bucking evident. Maybe related to distributor air gap, or being about maxed for advance.
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combatcarl

EGR is functioning properly. Now just fueling.
One thing I wonder about, is the accuracy of my timing light. It's a harbor freight, one of the adjustable ones, the knob came off, and I put it back, taped it on to prevent it falling off again or moving. I could have too much advance on it, and the light is lying. Could be the apparent ping under load.

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combatcarl

Haven't gotten around to getting a fuel pressure test done. I'll do one soon as soon as I have a gauge that reads high enough. What I did find after reconnecting the battery after checking the coil resistances, was that my positive terminal on the battery may not have been tight enough. I haven't really had the opportunity to stick my foot in it, but it may have been some of the issue, if not all. Still need to find a good accurate timing light to check mine against, to see if my timing is off due to a crap harbor freight timing light.

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combatcarl

Well, did it again today, not sure if I got it to do it the second time or not, but the second time, it did the on/off/on switch thing. Saw the CEL blink, as I glanced at the tach, right at 2.5k. Thought "oh yeah, maybe a code for a little direction", but no. Checked as soon as I got home, no codes. Steady blinking light. So this week, I'll dig through everything again, check all my grounds and major plugs. Almost felt like I lost power for a split second.

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osv

so there isn't hardly any room left to turn the distributor in one direction?

something wrong there... I just got back from the rubicon trail, i'm too burnt out right now to think of what could cause this(timing chain off a tooth?)... but check out the pic in this thread... also the comment by snobdds:

"The timing will be exactly on when the adjusting bolt is dead center of the adjustment range on the dizzy"
https://www.yotatech.com/forums/f116...27/index2.html

combatcarl

Yeah. Has plenty of power. Timing chain/cam timing is correct. I'm starting to think my gun is junk. Just have to borrow a known good one to verify. Idles good, starts with a bump of the key, cold or hot, better now after finding the loose terminal on battery. Still the intermittent fart on acceleration though. Time to chase wiring.

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combatcarl

Still no closer to a fix. Ran it down to North Bend and back home, pulls hills and cruises just fine. Stick my foot in it, still a hiccup at 2.5-3k, not an ongoing stumble, just a single hiccup, and on down the road. Did oil change, filter, and coolant flush and fill today. Rechecked timing, used an old gun for it. Waaay better strobe, and I think it's dying, wouldn't always stay on. But it told me I was a degree or two advanced from what I should be. Here's the hookup. I used this when I was a kid, no idear how old it is.


Had to use a paperclip under the boot, as I couldn't find the spring that goes on top of plug, under the boot. It works. Pretty damn well, too. Thanks, old farts that gave me the idea.
As I was re-timing it, I could see the mark wandering, even with E1-TE1 jumpered. Anybody else think that ain't quite right? Not a bunch, but a half degree to a degree. Maybe I'll try getting some video, if that doesn't make sense.

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osv

it wasn't perfectly steady when I set it on mine, you kind of have to wing it.

the spec is for the timing to be set at a certain rpm... I got a new timing light just so that I could do that, because it including a tach... it was reasonably cheap.

there is still something wrong with your distributor setting, because there isn't any room to turn it, to advance the timing... that is not right.

combatcarl

Well, there is room to advance it. Just not a lot. Most of the distributors I've seen sit around the middle of the slot for advance/retard. And most of the stuff I've set timing on doesn't have any variance in the mark. The 76 351W I used to do would sit rock steady. Same for the old 360 and 390. It may be a distributor issue, I think the things made about 700 billion rotations, and the bearing seal doesn't look so great. I'll figure it out, just posting to keep things updated. Most of what I found for threads just kind of die, with no solution or results on a fix. Kills me.

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