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1G JMF manifold

Posted by TK9er, Nov 23, 2020

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  1. TK9er

    TK9er Proven Member

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    Hey, I installed a JMF street manifold and some kelford 272s as well as set of feal coilovers on my car. I had a guys come do a idle tune for me and we are having a horrible time. We got it good enough to get the car to run, but the idle is all over. I had a few things to fix with the throttle body (it wasn't returning to zero in link), and a couple other non throttle related items. So, I fixed the throttle body and did a boost leak test. I had some air coming in around my new throttle body elbow. I replaced the gasket, sanded the elbow so it was flat, and I'm still getting air from around the bolt heads. So, after that long explanation, is it normal to put thread sealer on the throttle body bolts on a JMF manifold? And secondly, why does my car go from 1500rpms to 500?!?!?!?
     

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  2. iugrad92turbo

    iugrad92turbo Supporting Member

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  3. TK9er

    TK9er Proven Member

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    I guess I should have explained more. I have replaced the isc motor with the new black one (and double checked the coils) rebuilt the throttle body with new seals, have a FIAV bypass plate on, the biss doesn't leak (though I'm having trouble getting this set right following the online instructions), new injectors with new seals, I have the tps set right, the car does hold boost when tested (no major leaks), but I'm getting leaks around the bolt heads. I will run through the trouble shooting again, but it's not the first time I have gone through it.
     

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  4. TK9er

    TK9er Proven Member

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    Also have new coolant temp sensor.
     

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  5. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Is your Idle Stop Switch also adjusted correctly or simulated in LINK via TPS adjust?
     

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  6. TK9er

    TK9er Proven Member

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    I'd have to double check, but to think it is simulated... Does that sound right?
     

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  7. bastarddsm

    bastarddsm Proven Member

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    Unplug the isc, and work on the tune to get a stable idle. Might have to turn off closed loop. You will probably need to end up at 1100 or so warm idle with those cams/intake. Once the tune is good, plug in the isc, cycle the key and readjust the biss for correctly.
     

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  8. TK9er

    TK9er Proven Member

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    That's a lot higher than I thought, but that is fine with me. Would you be worried about the small leaks around the throttle body bolt heads?
     

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  9. TK9er

    TK9er Proven Member

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    And a question about the ISC. How does unplugging it help? When unplugged is it in the "neutral/middle" position?
     

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  10. iugrad92turbo

    iugrad92turbo Supporting Member

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    Small leaks around the throttle body, then you have a boost leak, any leak will be relevant fix that leak, i have a jmf with a stock throttle body, i had some leaks, simple fix, my bolts werent tight. No need for anything else in that area,. but your gasket. Sounds like you have boost leaks. You may have to do it, again and, you could have bad coil, did you test your isc to make sure its in spec?
     

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  11. TK9er

    TK9er Proven Member

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    I did check the coils they tested good.

    Did you have to make an adapter to mount your stock throttle body? The bolt pattern was the same, but I had to make a piece to cover up the larger opening. I have replaced the gaskets like 2 times . Gonna go broke paying shipping on gaskets! I have been making my own out of generic gasket material. Might get the actual gaskets this time...
     

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  12. Vegas Smith

    Vegas Smith Proven Member

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    It's pretty clear that you have a vacuum leak at your bolt holes that's causing this problem. I've heard of people using rtv or whatever sealant for the Sheetmetal tb bolts. Something about the way the bolts go into the manifold plenum to cause a leak whereas the stock manifold has studs that bottom out into the flange. Fix all your vacuum leaks then go through this entire page. https://www.sixsigmatuning.com/dsm-idle-control

    If the car has vacuum leaks then it's not even worth responding to any other questions about the idle because leaks mess with it so significantly.
     
    Last edited: Nov 23, 2020

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  13. iugrad92turbo

    iugrad92turbo Supporting Member

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    Nope no adapter needed for my jmf, and stock tb, i had leaks at the gaskets tightened it up and done. No more leaks.
     

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  14. TK9er

    TK9er Proven Member

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    I wish mine was that easy. I have had the throttle body off probably 5 times now... Tightening, replacing, and inspecting...
     

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  15. TK9er

    TK9er Proven Member

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    Thanks, that is why my initial question was about thread sealer. I might try some teflon tape.
     

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  16. TK9er

    TK9er Proven Member

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    Thread tape baby! No more leaking bolts. I got it up above 25 psi. I then blew off the tester. I do have bubbles coming from the adjustment screw on my fuel pressure regulator. Is that normal?
     

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  17. DSMPT

    DSMPT Proven Member

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    Don't you have a 90 throttle body? If you do, aren't you using a 91-94 throttle body gasket? If so, you may have a massive boost leak at the bottom of the flange where the green circle in the pic. The first pic is a 90 throttle body with a 91-94 gasket. Please refer the pics.
    Or I don't remember if the JMF intake has a flange that fit with a 90 throttle body. Perhaps the flange doesn't have enough area to cover the 90 throttle body.
    DSC_2546.JPG
    DSC_2544.JPG
    DSC_2545.JPG
     

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  18. TK9er

    TK9er Proven Member

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    Thanks, I swapped it over to a 91 and up throttle body.
     

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  19. bastarddsm

    bastarddsm Proven Member

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    The isc is a stepper motor, and it will be in whatever position it was in when you unplug it. That's why you need a key cycle when you reconnect, so the ecu will "home" it and remember where it is. You might need to cheat the idle up with the biss, and or the closed throttle switch if the isc is closed too much.

    Basically the idea is less knobs to turn. The ISC is really slow to react to changes in idle speed. Couple that with a tune that isn't stable and you get surge. The tune makes the idle sag, the isc starts opening, and opens too far, idle speed rockets, isc slams closed process repeats. For someone like me who has a good handle on things it's not a big deal to get it straightened out, but for someone with less experience, having the isc moving around and changing things can make it harder to see what's going on. Closed loop fueling can drive this as well for the same reasons. Big cams don't generally don't play nice with the o2 sensor at idle since there is so much overlap/reversion, and it kinda skews the readings and can drive oscillation through fueling changes. I'm not super familiar with this side of ecmlink, but on my ecu for example I can change the pid gain vs rpm and load to make closed loop less sensitive at idle.

    It pretty much boils down to if the car won't sit and idle stable without an isc, it's not going to be stable with it. Obviously things like the fans kicking on, or a/c or power steering draw will pull it down. You need to have the tune up so you can put the car on the 2 step, let it build boost, and then chop the throttle shut, and it snap right down to 1100 a little undershoot is ok, but it shouldn't die. If it can't do that, the isc won't save it.


    Think of this whole deal as a ball sitting on a surface, and the center of that surface is your target idle speed. Say you have an absolute perfect tune, that surface is flat, and if you disturb the idle off target just a bit, the ball doesn't keep rolling - it stops and is easy to put back in place. Say the tune is all boned, and we will represent that with a convex surface - disturb it a little bit, and the ball can run away down the hill and you might not catch it. Say you do, and you get it back to target, but maybe just go a little far, it runs away this other way. This is called positive feedback, and it drives oscillations.
    What is possible a better approach is a bit of negative feedback, make that surface just a bit bowl shaped, so if you disturb the ball, it has a natural tendency to return to center. You can pretty easily do this with timing. Keep the map flat in the area you idle in, and possible take a little timing out above target, and add a little below. It's probably possible to accomplish this with fuel as well, but harder since torque is not very sensitive to fuel until you get way far out, then it drops like a rock so keep the fuel flat.. With those cams I'd probably disable closed loop till say 2000ish, and try to target just a little richer than stoich at idle, and try to keep the afr flat in that area.

    All this hinges on having the mechanicals in order. If you are on speed density a small leak probably won't matter much, but it's prudent to correct it. I don't think I'd use teflon tape. I'd probably go for something like a small dab of ultra grey, or permatex moto seal, or even red loctite should seal threads up well.
     

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  20. bastarddsm

    bastarddsm Proven Member

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    Got a picture of your intake, and intake opening. Sounds like something there isn't right. I had a billet JMF drag on mine for a while and it sealed up just fine with no f***in around at all.
     

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  21. TK9er

    TK9er Proven Member

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    Attached Files:

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  22. bastarddsm

    bastarddsm Proven Member

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    Looks like mine. Has the 70mm opening? That's what mine is and I'm running a 91 n/t tbody on it.
     

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  23. TK9er

    TK9er Proven Member

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    That's it before installed it.
    Yep, my TB is a 91 turbo throttle body. I must of deleted the picture, but without the spacer I made, the throttle cable side of the opening was not covered. I made a 3/16 spacer to cover the gap.
     

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  24. Vegas Smith

    Vegas Smith Proven Member

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    I had that same leak on my Fuelab regulator and put some sealant on it. I doubt it does much but can't hurt.
     

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  25. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    I wish I had looked at the thread earlier. Sorry OP.
    One problem I am sure was the 90 TB. On my Evo3 mainfold, that thing leaked HORRIBLY. Switched over to the 91+ TB and fixed it. The 90 TB has a different cutout area on the back side that usually never seals on the other flanges. I don't know why, didn't dig into it, just addressed my problem and put the 90 TB on a shelf. Now I have a 90 GSX build that needs that TB so it all worked out good.
    Just some of my 1990 experiences that are weird.
     

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    1967 Chevrolet Camaro RS
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    1990 Eagle Talon TSi AWD
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