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S14 hesitation at WOT

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  • Pavel
    started a topic S14 hesitation at WOT

    S14 hesitation at WOT

    Long time E28 M5 owner, jumped over at the S14 side for a short while now, while helping a friend get his car baselined.

    I have been fighting this E30 M3 for while now, and can't seem to find the problem. Sort of. The car ran fine before valve adjustment, cap/rotor, sparks and new wires. This is when I got it, with the issue below. None of the original components are available to swap back over.

    At WOT the engine will hesitate and take a good 2-3 seconds to rev. Upon load, taking off from a stop it will even die. If i do partial throttle, the engine is accelerates fine.

    So far, I have replaced the ICV hoses #16, 17 as they had signs of deterioration https://www.realoem.com/bmw/enUS/sho...diagId=13_0285

    Also cleaned the ICV.

    JB Welded the elbow at the throttle bodies. The elbow at the intake is fine. Smoked the engine with a fog machine, no clear visual leaks. I haven't checked the brake booster elbow, but might do that next.

    ITB balance and sync, valve adjustment (redone, no issues found), fresh o-rings on the ITBs and the adjustment screws. Two different 028 AFMs tested (from a good known car). Adjusted the orignal AFM to the car, to read roughly 0.5V at the 02 sensor.
    a
    Spark plugs are NGK, and bremi wires. Idle set at 850rpm with bridged TPS. It goes up to 910-20 rpm when TPS reconnected.

    Different TPS tested too (verified good as well).

    At one point, I thought I nailed the problem as a vacuum leak at the valve cover. But today after swapping from a good set of Bosch X5DC back to the NGK, and redoing the smoke test, I ended up back to square one. Just replaced the airbox to intake elbow. Now i can't get it to run normal again.

    I get about 10-12cmHg when reading vacuum at the ITBs. So i attribute it to vacuum leak still, but why it changed so abruptly from being OK back to hesitation, I am not sure.

    Any pointers will be appreciated!

  • proctor750
    replied
    I would still try swapping in stock ECU with confirmed factory chip along with the stock cam gear with correct timing and see what happens as a last ditch. Definitely sounds like the motor is due for a refresh though...

    Also you could do a wet compression test and compare the numbers to dry. I believe you just need a tablespoon of oil down the cylinder then crank 6 more rotations per cylinder and if the numbers go up the rings are probably no good.

    Leave a comment:


  • irdave
    replied
    Originally posted by basketcase View Post
    Been thinking about this. I've had over the years bikes and cars with low compression/bad rings that have similar symptoms to you. Like under any type of load (ie AC on) the engine would die once clutch is let out. At high revs the engine would operate fairly normally.

    Low compression = low torque.
    Your leakdown figures and compression figures are to me obviously an issue with this engine. 160 psi compression? Mine was 230 after a rebuild, and that's a common figure for s14s. 160 psi is stock figures for a e30 325i M20 engine, which has 8.8:1 compression from factory.

    Also your leakdown figures of 25-30% to me indicate an issue. I regularly do leakdowns at work (I am a BMW technician) and the norm for a engine with no issues is 5 or 10%.

    You have replaced everything on the engine... Maybe address the mechanical issues and retest after. Ie new rings.
    I'm new here so forgive me for jumping in, but this. I mean, you're rolling each piston to TDC compression for each individual leak down test and locking it there, yes? If so and 25-30% loss of pressure- the engine needs love... Flip side, engine will run WAY better.

    Leave a comment:


  • Pavel
    replied
    Terence237 Yeah I swapped coil early on.

    basketcase I have been going back and forth with this same thoughts - rings. I am not sure my else is left. Quadruple checked all my work.

    I borrowed a friends' M3 to try a few things. Swapped ICV last night (which I had previously done as well) between the cars. ECU next (stock chip). I am going to get compression and leakdown on the said car, as well just for comparison. Log some of the data plots, i did earlier.

    Leave a comment:


  • basketcase
    replied
    Been thinking about this. I've had over the years bikes and cars with low compression/bad rings that have similar symptoms to you. Like under any type of load (ie AC on) the engine would die once clutch is let out. At high revs the engine would operate fairly normally.

    Low compression = low torque.
    Your leakdown figures and compression figures are to me obviously an issue with this engine. 160 psi compression? Mine was 230 after a rebuild, and that's a common figure for s14s. 160 psi is stock figures for a e30 325i M20 engine, which has 8.8:1 compression from factory.

    Also your leakdown figures of 25-30% to me indicate an issue. I regularly do leakdowns at work (I am a BMW technician) and the norm for a engine with no issues is 5 or 10%.

    You have replaced everything on the engine... Maybe address the mechanical issues and retest after. Ie new rings.

    Leave a comment:


  • Terence237
    replied
    Did you try to change your coil?

    Leave a comment:


  • Terence237
    replied
    Hi Pavel,

    what a frustrating issue. Hopefully you Can find the problem soon!

    Leave a comment:


  • Pavel
    replied
    It's a cheap test, worth a try. I did test with a different ECU, very early in the game but w/o knowledge if it had stock chip or not. Thanks for the suggestion.

    Leave a comment:


  • stevesingo
    replied
    Put a stock chip in and try it.

    I don't have any faith in chips. Ill the advance curves I have seen over the years are obviously over advanced. No wonder there are so many big end bearing failures.

    Leave a comment:


  • Pavel
    replied
    Originally posted by stevesingo View Post
    Do you know how much ignition advance it runs at idle?

    I think we may be on to something here.

    If the ignition is retarded, then for a given load, you need more air. More air is needed the lower the vacuum.
    That is an interesting point! I wonder if that is available anywhere, as a spec for the chip.

    I personally have noticed no difference off idle on a S38 with Evo gear Advanced with stock chip, Jim C, or Dinan. I have tried all three chip variations, on the same engine.

    Leave a comment:


  • stevesingo
    replied
    Do you know how much ignition advance it runs at idle?

    I think we may be on to something here.

    If the ignition is retarded, then for a given load, you need more air. More air is needed the lower the vacuum.

    Leave a comment:


  • Pavel
    replied
    Originally posted by stevesingo View Post
    When you say Dinan, what do you mean?
    It has a Dinan Chip.

    In the S38 world, the Dinan Chip paired with a Retarded setting on EVO gear, allows for the torque shift. The JimC chip was designed for the Advance setting of the gear - per Fahey. My understanding is there is no point in shifting the torque to the top in a S14.

    Leave a comment:


  • stevesingo
    replied
    When you say Dinan, what do you mean?

    Leave a comment:


  • Pavel
    replied
    Originally posted by stevesingo View Post

    From the canister purge vac line.

    To be honest with you, the response to the throttle does not look too bad with AC off.

    If you hold the engine at 2000rpm and snap the throttle open to WOT, how does it respond?

    These engines are pretty highly strung compared to a modern engine or indeed a larger engine. What did you drive before this car?
    My experience with 3 other S14s is not similar - stock M3, 2.5 M3, and S14 swapped 2002 (with an aftermarket engine management). My personal cars are all 6 cylinders - S38, S50, M106. I have built two E28 M5s at this point. Hence the reason I donít believe the leakdown is the problem, but that is the only thing I can go by.

    The car drives fine at speed. I would actually say not bad at all. Response at 2k and to WOT is good.

    Not sure, but this is the first EVO geared + Dinan M3, and maybe that is affecting timing and idle vacuum.

    Leave a comment:


  • stevesingo
    replied
    Originally posted by Pavel View Post

    Where would you measure vacuum with a gauge?
    From the canister purge vac line.

    To be honest with you, the response to the throttle does not look too bad with AC off.

    If you hold the engine at 2000rpm and snap the throttle open to WOT, how does it respond?

    These engines are pretty highly strung compared to a modern engine or indeed a larger engine. What did you drive before this car?



    Leave a comment:

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