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Thread: Weber carb hesitation under load...

  1. #26

    Dr_Snooz's Avatar
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    Re: Weber carb hesitation under load...

    If you remove the hood, would you be able to see FP gauge while driving?
    Dr_Snooz

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  2. #27

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    Re: Weber carb hesitation under load...

    I got it on the dyno this weekend. I'll have to post the chart. You can see the power completely disappear at 3000rpm. The air/fuel ratio starts getting a little bit more rich as the RPMs climb, even while it's hesitating, but it's not out of whack enough to cause the huge power loss. We were able to watch the fuel pressure on the dyno, and it looked good too.

    What you can see on the chart over 3000RPM is power spikes, where its completely unsteady and climbs and dips. The tuner at the shop said it's definitely an ignition problem when I showed him the dyno chart, long before I ever mentioned it was carbureted. So I need to somehow test the pickup sensor on the trigger wheel, or replace it, and take the wiring apart and redo it. I think there's gotta be a bad ground or loose connection or something somewhere in the harness I built for the Megajolt. Maybe this is why you should use butt connectors instead of solder?

    Sorry the thread has been so hard to follow, it's just this long, retarded chain of events that I can't even keep straight in my head. I let some of these problems go too long after they started popping up.

  3. #28

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    Re: Weber carb hesitation under load...

    As I understand it, your A/F ratio should get slightly richer as you approach WOT, so that's working fine. Very interesting problem. I can't wait to see what you find.
    Dr_Snooz

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  4. #29
    2.0Si User Hazwan's Avatar
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    Re: Weber carb hesitation under load...

    Solder > everything else, as long as its done properly it should last forever. I have yet to see any of my connected/spliced wires/connectors fail even after 3+ years of use.

    I've seen many failed poorly crimped terminals and of course, twisted and taped wires before soo

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  5. #30

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    Re: Weber carb hesitation under load...

    I could see at least part of the spikes being carb transistions, generic powr valve parameters, sec idle jet selection, air correcter and emulsion tubes that may not be ideal for altitude or other enviornmental properties.
    That is awesome you were able to see it on the dyno, I bet that is exciting to know your car has power & performance yet to be unleashed!

  6. #31

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    Re: Weber carb hesitation under load...

    Well, the power doesn't just drop off a little bit, it's completely gone. Torque goes from ~95lb-ft to about 30lb-ft. Can't be a jetting issue. Couldn't even get the car to pull up past 4000RPM until I got it down to 2nd gear.



    And check out the air-fuel ratio on the blue line. That was the run where I was able to pull it higher up in the RPM range. It's pretty damn spot on, and just starts getting richer with the misfiring. But it's not rich enough to cause that kind of power loss. I mean at 4000RPM, it's still well above 13:1AFR.

  7. #32
    3Geez Veteran Rendon LX-i's Avatar
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    Re: Weber carb hesitation under load...

    Just as a witness is my prospective. its a ignition issue for sure. has to be with the hall effect or wiring. one of the two you did mention that the air gap is dead on from what you told me was 1mm correct? but most certainly a ignition issue. Lmk what happens john.


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  8. #33
    2.0Si User Hazwan's Avatar
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    Re: Weber carb hesitation under load...

    Dat torque o.o

    I would love to see how much you're making with a properly running engine now ahh!

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  9. #34

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    Re: Weber carb hesitation under load...

    The shop said they'd let me have an hour of free time with their tuners there to help out. So once it's running right, and with the help of the MegaJolt and my jet kits, should have it tuned in to perfection.

  10. #35

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    Re: Weber carb hesitation under load...

    good good (Y)

  11. #36

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    Re: Weber carb hesitation under load...

    So I'm still having this strange problem. I'll try to re-summarize what I've got going on at this very moment:

    Hesitation under heavy "load." I say heavy load, because it requires a lot of throttle at low speeds, but on the freeway, even a little bit of extra throttle, like going up and incline causes this hesitation.

    My other symptom is flickering lights. Like the cabin lights, dash lights, and headlights. I feel that this electrical problem is likely what's causing the hesitation, and a bad spark that can't ignite the denser air-fuel mixture... or possibly no spark.

    I replaced the alternator, main grounds, and tried 3 different voltage regulators, and this light flickering still seems to happen. Only thing left to check is wiring? I'm not really an expert at that part...

  12. #37
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    Re: Weber carb hesitation under load...



    200+ ALL MOTOR LS VTEC

  13. #38
    2.0Si User Hazwan's Avatar
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    Re: Weber carb hesitation under load...

    ^ good links.

    When you say flickering lights, are they only when the engine is running or doing the same even with the engine off? Whats the voltage reading like?

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  14. #39

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    Re: Weber carb hesitation under load...

    Thanks Josh! That Voltage Drop testing looks like the fucking ticket. I had no idea about the multimeter actually measuring the voltage difference between the leads. Damn, that is super fucking helpful. And now that gives me a lot more ability to go through and test my wires! I've been tearing apart harnesses and looking at wires, but having no actual idea if the circuit is any good deep down in the harness. I can't wait to start testing stuff tomorrow night. I figured even a shitty connection I'd see 12v, but not know if it was actually a good connection or not. This is awesome.

    Hazwan, the headlights only flicker when the car is running. I actually even started the car with the plug on the alternator disconnected (the 3 pin connector) and there was no light flickering then. The weird thing is that the voltage actually looks steady with my meter, but it is the cheapo $3.00 meter so maybe it's not fast enough. Around 14.5 volts or so when charging and like 12-13 when the engine isn't running. Maybe I should borrow the Fluke from work.

    What alternator did you wind up using on your car that has the built in regulator? I'm guessing there are a million that will fit, but when I eventually do the wire tuck (yes asking for more wiring hell) it will be nice to not have the voltage regulator over by the battery, and it would be nice to eliminate all the unnecessary wires.

  15. #40
    2.0Si User Hazwan's Avatar
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    Re: Weber carb hesitation under load...

    That sounds a lot like alternator issue to me or the regulator issue I don't know >< Knowing these cars I wouldn't be surprised if the 3 wires from the alternator to the voltage regulator is old. You did bypass the stock main charging cable with the jumper cable before too right? One more thing left to do would be testing each of the 3 wires from the alternator to the regulator for resistance, if its too much then it might be possible that the alternator didn't know the exact battery voltage and would kept trying to charge like 15v and then realized oh nvm its too high, going back to 14ish and it would go on forever causing your flickering lights issue. I'd check the main charging wire for resistance too.

    I used a Sentra B11 alternator or at least thats what the parts guy said. Everything lines up perfectly, minus the 3 pin plug, its 2 pin for the Nissan alternator I think? idr lol but yeah you just gotta bypass the external regulator obviously and boom (Y)

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  16. #41
    2.0Si User Hazwan's Avatar
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    Re: Weber carb hesitation under load...

    One more thing since you said you multimeter shows a rather steady voltage.. I would check the underdash fuses/main battery cable (fat white single connector) going to the dash harness. Thats the main power cable for the rest of the cars electrical system, lights, fans, engine etc.

    It could be old and been causing every single of your problems too. Check for the resistance for that fat cable and the positive cable or at the main 55A fuse too. Or check the voltage at the fuse box/fat white cable and see if you get anything weird.

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  17. #42

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    Re: Weber carb hesitation under load...

    All awesome ideas. I'll probably have to wait until tomorrow night. Also, I need longer leads for my meter!

  18. #43
    2.0Si User Hazwan's Avatar
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    Re: Weber carb hesitation under load...

    Some random wire connected to the end of the lead will do the trick

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  19. #44

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    Re: Weber carb hesitation under load...

    Quote Originally Posted by 2ndGenGuy View Post
    The weird thing is that the voltage actually looks steady with my meter, but it is the cheapo $3.00 meter so maybe it's not fast enough.
    An analog meter would be better for capturing fluctuating voltages.
    Dr_Snooz

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  20. #45

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    Re: Weber carb hesitation under load...

    I should probably have an analog meter...

    So I went through and did the voltage drop tests. All my ground points seem solid, there's no voltage difference at any of them that I can find.

    I tested the 4 connectors on the alternator. Worst drop I saw was 0.3v on one of the wires, and something like 0.1v on the rest of them.

    I tested the power connections in my harness I made to the coil pack and to the EDIS ignition control module. Got strong voltage there. Ground to that seems to be excellent too.

    I tested every circuit in the fuse panel. 0.3v drop was what I saw on everything, except the headlights, I saw a 1v drop. Doesn't seem to be anything of a concern.

    I did do a voltage test on the VR sensor. Supposedly, you're supposed to have 2.5v AC when cranking the engine. I only got 1.3v. So I'm not sure if that means it's bad or what. I did re-solder the connections to it, since I did a shitty job on one of the wires, and the car is a LITTLE better now, but not much.

    My other question is, can the spark plug wires be a concern if they are close to a ground or anything? They do run a little bit close to the alternator, but they don't touch it... It wasn't a problem before though, but I do want to eliminate everything. They are brand new though and they don't shock me when I touch them, so I don't feel like it could be the problem.

  21. #46
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    Re: Weber carb hesitation under load...

    Seems to me like either the coil can't keep up (and is putting out too weak of a spark) OR your total timing isn't "broad" enough. I've had the dead spot issue before, I.E. She just WOULDN'T go over 4000, no matter what, the problem was basically I had the timing advanced (or retarded?....can't remember) and essentially the timing wasn't advancing enough for the engine to actually work any faster than 4 grand, it was acting like a governer.

    I would either try to tweak your timing curve or check for lack of movement in your advance mechanism, BUT you don't have a Distributor anymore do you? I guess I'm not much help but I really do think it's either a spark strength or spark timing issue.
    Have you changed the octane rating of gas you use?
    It seems trifling, but assuming you tuned your timing by using a particular octane rating, buying a higher octane fuel would move/change the ideal ignition moment. As for the spark plug question, yes, spark will always take the easiest path to ground, so even a tiny little crack in the wires can cause big problems.

  22. #47

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    Re: Weber carb hesitation under load...

    I know a lot has been done since #1 so can you say exactly what the symptoms are now and which one is unchanged without varience? I know on my Ford the set up stays the same but sometimes it won't get out of it's own way, the variables are fuel quality and air temp. Sometimes it runs great , had a certain tone in the engine that sounds right.
    My B20 carbed does the same thing but the air temp is a huge deal with it, i should have never drilled those divots in the plenum floor. These carbs really need spacers o even swirl spacers like they make for toyotas. The fuel/air charge needs to build or disperse a little more before leaving the plenum. Of course heating it accomplishes a lot of that, makng more gas than liquid... This is where the fuel blend differences come into play I suspect. A real cool humid day the car runs like crap.
    It also makes a lot of sense that an ignition problem could affect the carb mixture transistions, especially timing curves. It would be chasing gremlins to keep making changes on both ign and carb without documenting each action and timeline.
    Last edited by 2oodoor; 05-04-2013 at 05:43 PM.

  23. #48

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    Re: Weber carb hesitation under load...

    So, what 5 months later... I finally got off my ass to try to figure out what's up again. I've been using the car pretty much exclusively for short trips around town, but I can't commute to work, since 50mph is about my top speed.

    So I threw a distributor in the car, to try to isolate the problem, and see if I was right to suspect the MegaJolt. And it turns out that the EXACT SAME PROBLEM is still happening. While I'm super glad that I did a proper job, and that my MegaJolt wiring was not the problem, I am bummed as I can't figure this issue out for the life of me.

    I mounted a fuel pressure gauge out on the cowl of the car that comes up through the hood. Fuel pressure does seem to dip down to about 1psi after a sustained load on the engine. So maybe I should get a different type of fuel pump, or maybe my wiring to the fuel pump is weak and the pump isn't getting enough juice. I'm going to run some fresh wires on a dedicated circuit to the fuel pump and see if that does anything. The stock pump never had problems keeping up with the engine for the last 4 years...

    Also as a side note I do still have the headlight pulsing when the alternator is kicking in to the high output mode (IE, RPMs over 1000). So I'm still suspecting some kind of major electrical issue with the car. Maybe today is the day to rip the harness apart and see if there are some broken wires or something...

  24. #49
    2.0Si User Hazwan's Avatar
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    Told you to put a fuel pressure gauge before lols but good luck!

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  25. #50

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    Re: Weber carb hesitation under load...

    Quote Originally Posted by 2ndGenGuy View Post
    Maybe today is the day to rip the harness apart and see if there are some broken wires or something...
    Oh... goody!
    Dr_Snooz

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