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Old 09-19-2011, 09:14 AM   #1
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Default Car Bogs Out before 4k RPMS

Hi Everyone,

So as some of you may know, I have been trying to get a MSPNP to work in my car but as soon as i put it in, my car doesnt start and doesnt get spark. Regardless that is not the reason for this thread. I went back to the stock ECU and whenever I try to get on the car at low RPMS, the car just bogs and cuts out...If i give it gas slowly until 3500-4k rpms and boost comes on, I can punch it and it pulls great all the way to redline. Is this a timing issue where the timing is off in low gears? My car is a 1991 miata with the greddy turbo kit, a FMIC, blue top injectors (out of an rx7 i believe) it has the Vortech fuel regulator. When the car does bog out the AFRs seem good and then just peg lean...So it almost seems like the more gas i give it just bogs it out? I dont know why the wideband then goes lean? Any input you guys have on this would be helpful. Also I just recently put new spark plugs and wires in the car so i know its not those. Put the ngk blues in it like people on these forums suggested when i searched. I would love to find a way to make this car run well, and as i said the MS I have does not seem to want to play nice with my car.

Thanks for any help.

Tyler
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Old 09-19-2011, 11:24 AM   #2
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Post a datalog of this happening. Post your msq.

without those, we can mostly just guess wrong and send you on a wild goose chase.
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Old 09-19-2011, 11:27 AM   #3
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thats the thing, i cant get the car to run with the MS installed no matter what I do. Could be something wrong with the MS unit i purchased, im not sure. So as of now my car is on the stock ecu with just the vortech fuel pressure Regulator. So I was wondering if there was anything i could do with the stock ecu in the car...?
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Old 09-19-2011, 04:32 PM   #4
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Any chance this could just be due to timing for some reason? Aside from the Vortech unit I dont believe there is anything controlling the timing on my car from on to off boost...As I said i just bought this car so I am trying to make it right...
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Old 09-19-2011, 04:45 PM   #5
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So what exactly happens when you attempt to start the car with the MS installed? How much boost are you running? Does the exhaust smell rich, or does it look black?

If the MS is a DIY maybe the person who put it together did something wrong?
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Old 09-20-2011, 11:26 PM   #6
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Dont worry about the MS...For right now im curious why my car just BOGS out before 4k rpms. The car has new plugs, wires and a new O2 which was not fun to remove and was eve more of a pain to put back in but thats another issue. The same bogging was there and if i give it too much gas anywhere below 4k rpms the car literally goes full lean and just cuts out as if it is starving for fuel, which it seems like it is...but its weird because im giving it alot of throttle. Thoughts?
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Old 09-21-2011, 11:06 AM   #7
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Going to be checking the timing again tonight and seeing if that makes a difference. Do you think there could be something wrong with my crank? I have 8 slots on the pulley so i believe i have the long nose crank so i dont think that is the issue
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Old 01-09-2012, 11:45 AM   #8
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Hello Everyone. I am wondering if I can resurrect this thread I have and see if ther are any other suggestions for why my car is still not running right. I tried to install an o2 clamp from olderguy but am still not getting enough fuel below 4k rpms. Could this be related to the AFM? Could I need bigger Injectors? It is just odd to me because above 4k rpms the car runs well and does not bog. This makes me think it is electronic.... I refuse to believe that I am the first person with this issue. I am not looking to get a new ECU yet and am just looking to band aid fix this for now. Any input is appreciated.

Thanks
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Old 01-09-2012, 12:44 PM   #9
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Timing. FPR installed incorrectly. Both. Vacuum leak. Lots of things brah.
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Old 01-09-2012, 12:47 PM   #10
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It seems to be a FPR issue or fuel pump. Have you even messed with the fuel pump? Also, if you want to install the MS, then you need to uninstall the Vortech to do it correctly.
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Old 01-09-2012, 12:58 PM   #11
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Checked for vacuum leaks and did not find any. Vortech FPR seems to be hooked up correctly. Have checked the timing and that is correct.... What is weird to me is that above 4k rpms it is fine. If I want to enter a corner fast I have to downshift to make sure the car is above 4k rpms or with any load and giving it gas it will bog and go lean. I am wondering if it could be the engine temp sensor? I know there is one that goes to the gauge and one that goes to the ecu. Could it be possible that this sensor is bad and causing the ecu to think it is running too hot and then it is pulling fuel below 4k rpms? And then maybe at the 4k mark it disregards the signal? I am researching this as much as I can and it definitely seems electrical because the AFR is OK above 4k rpms. Is it perfect? No but above 4k rpms under boost about 5psi it is around 13 ish... I know it could be lower but that seems OK to me. Doesnt this seem electrical because of the night and day difference between below 4k and above? Is the temp sensor a possible culprit?
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Old 01-09-2012, 05:25 PM   #12
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I have been doing some more research and my problem seems very consistent with the Surging issues that are associated with a bad TPS. I know that on my miata 91 1.6 Manual it is just a switch but if there is something wrong with it it could be causing the ecu to go nuts? The only thing I am still struggling with is why it is liked to RPM and not nessecarily to Throttle position. Because above 4k it is fine. Thoughts?
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Old 01-09-2012, 05:36 PM   #13
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My thoughts are without actually testing things, you will just end up replacing an *** ton of parts. A great start would be to put your car back to stock and see how it runs. Or at least wire wastegate open so you run no boost and see if the problem persists. Removing the FPR would be great as well, although it technically shouldn't be doing anything if you run no boost.

You should in no way be taking turns fast if your car is running like ----. What CC are the RX7 injectors you have? What wideband do you have? Like y8s mentioned this probably won't get far without you running your MS so we can see a datalog.
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Old 01-09-2012, 05:40 PM   #14
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Quote:
Originally Posted by daytona675 View Post
If I want to enter a corner fast I have to downshift to make sure the car is above 4k rpms or with any load and giving it gas it will bog and go lean.
How lean? (IOW, do you actually have a wideband EGO sensor, or are you just guessing?)


Does this happen only below normal operating temp, or is it an all-the-time thing? I ask only because I've come to regard this behavior as normal on 1.6 cars running the stock ECU when the engine is cold. Both of mine did this- virtually no power at all below 3-4k until the temp gauge was at the normal position.

Wasn't related to the AFM reading (the '92 continued to do this after I removed the AFM while still running a Greddy EMU). Hard to imagine how TPS could be causing it, as you don't really have one. (Well, I suppose a 1.6 TPS locked at "idle" might potentially have some weird effects, but that's difficult to imagine.)

Megasquirt solves all.
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Old 01-09-2012, 05:47 PM   #15
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I have removed the FPR and the issue was still there but the car was running much leaner. I have sold the MS because the one I had would not work with my car (I dont know if it was the unit or what the deal was). I am running an AEM Wideband. And the injectors have a blue top. So from what I have gathered those are the stock 1.6L injectors. So I am monitoring the AFR not just guessing and what is weird is that if I give it barely any throttle... it will be fine but I mean BARELY any throttle. just very little...till 4k rpms...then I can give it gas and it goes. If I try and give it gas below 4k RPMS it will get to a point in the throttle and then feels like the ECU is just pulling fuel and I can see the air fuel guage go lean...sometimes it will almost bounce and go nuts...lean rich, lean, rich...like the ecu is pulling fuel then allowing fuel.
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Old 01-10-2012, 11:06 AM   #16
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When I get home from work tonight I am going to disconnect the TPS and see if that makes a difference. Until then does anyone else have any suggestions or ideas as to why this bucking / surging could be happening?

Thanks
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Old 01-10-2012, 11:34 AM   #17
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Anytime you misfire, for any reason, your WBO2 will read lean. The WBO2 is an oxygen sensor, and if you misfire, oxygen will be present. When you're not misfiring, what does the WBO2 read at idle . . . at 2K . . . at 3K. Also, have you retained a NBO2 for your ECU?

Bottom line, you haven't given us much to work with. The one suggestion to return to stock and go from there is a good one. I will say that acceleration enrichment is much more critical at low RPM's than at high RPM's to avoid bogging -- but that's just a stab in the dark.
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Old 01-10-2012, 11:38 AM   #18
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As I am still using the stock ecu it is using the stock nbo2 and the afr is OK at idle and 2k ed. Obviously it changes based on how much throttle I am giving it....
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Old 01-10-2012, 08:55 PM   #19
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Ok, its not the TPS...I am thinking it is one of the following. Let me know what your guys thoughts are. 1) Stock fuel pump may be going bad and just not able to deliver the amount of fuel the ECU is trying to deliver at low rpms. 2) Clogged fuel filter (This I suspect because after I went for a drive i heard a clunking sound coming from pass side by the rear wheel. Its odd and I thought it was electrical but im thinking it could be the fuel filter) 3) Bad ground to the ecu could be causing the car to not run right and have this hesitation? And then when it is above 4k rpms it works fine? Any other thoughts are appreciated. Thanks.
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Old 01-10-2012, 09:51 PM   #20
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1. No. Fuel pump is delivering plenty of fuel for high RPM, therefore it can deliver plenty of fuel for low RPM.
2. No. Fuel filters don't clunk when they're clogged. But, they should be changed out as part of regular maintenance. However, given that you run OK at high RPM, the filter is probably OK.
3. No. Bad ground would be intermittent and not traced consistently to an RPM range.

What about your stock fuel pressure regulator? Have you measured fuel pressure?

Also, what is your definition of "afr is OK at idle and 2k ed." You have a WB. Give us numbers.

I don't know why AFR would "obviously change based on how much throttle you give it." The stock ECU with NBO2 targets 14.7. It shouldn't be changing dramatically from that when you're in closed loop.
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