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Car spiking to 4k RPM's on start and can't figure out why
Car has a 1999 1.8L FMII Turbo and Hydra EMS.
The second I start the car it throttles up to 4k rpm and sounds like hell. Prior to the two things below it ran fairly well and had a solid idle at 850rpm's.
Pretty sure the issue is related to one of two things that I just did to the car.
Installed a new Skunk2 throttle body and I ported the factory upper intake manifold to match up to it. I did recalibrate the TPS in the Hydra, so technically this shouldn't be causing it. Not sure though. The idle control screw (red) is all the way in. I figured that would be safer to start and then adjust from there, but obviously the car is just going on throttle immediately. The throttle body cable slack is also set properly and bottoms out just as the butterfly fully closes.
Just replaced my old Flyin Miata Injectors with Flow Force injectors. Sent the FM injectors out for testing and cleaning and they came back as being pretty far off and was told they are no longer a matched set and to replace them. Checked for a fuel leak on the injectors and no gas anywhere, so it looks like they are seated perfectly.
Could fuel injectors cause a weird idle spike like that if the settings are wrong?
I did my best to set the injectors up properly in the Hydra, but there is no documentation on this and I already reached out to Ken Hill to get his help tuning the engine. Do you need to do anything other than change the flow volume and set the injector response?
Injector Response Chart - I tried to match it to the MS3 settings on the Flow Force site, but I have a feeling I screwed this up. You can see how it went super lean when I started it for a quick second (21.6 AFR).
I think the only thing that's going to make the car rev that high at idle is a leak between the throttle body and the motor. There's a lot of air getting past the throttle body that shouldn't be; either a leak in the intake manifold, big open vacuum port (like the brake booster), or a leak at the throttle body.
Yeah it's pretty easy to put the iac adapter on in such a way that makes a giant hole. You can try screwing the bypass valve all the way in, and make sure there's no stretch on the throttle cable .
Does it eventually settle down to a normal idle or does it continue at 4K ish ? My first thought is major vacuume leak. Fredb
That's weird, I thought that immediately too and does it does make a weird vacuum whine. Would a vacuum leak cause a spike like that?
I didn't want to wait it out to see if it settles. Scared the **** out of me to be honest haha. The super high AFR also made me not want to let it go for a minute. I'll go look over all the vacuum hoses to be sure everything is hooked back up fine.
Yeah it's pretty easy to put the iac adapter on in such a way that makes a giant hole. You can try screwing the bypass valve all the way in, and make sure there's no stretch on the throttle cable .
Can you please elaborate on that? The Skunk2 instructions for the IAC adapter were pretty rough and it took me a few tries to where I thought it was on right and not leaking.
I can't find a picture of the SKunk2 Miata TB with the IAC installed. Just want to confirm it is aligned correctly.
Woohoo! Making progress. There was a massive leak on the upper intake manifold from the front corner not seating all the way. Didn't have it lined up correctly with the fuel rail and it's a tight fit!
Car starts now and doesn't spike! It does idle for a sec and then dies. I think my injector settings just need to be corrected now and I'm good.
The injectors are roughly the same size, but completely different model.
Okay, went back and looked at the injector response (dead time) and found my numbers were off. I was looking at the MS3 numbers and getting confused. Nigel had the chart on his site right in front of me. Doh!
Anyways, here is the updated Hydra injector response chart and the values I used for anyone looking. Going to test them on the car now. Will update if this works.
Gahhh!!!!! Now the car won't start with the updated injector response settings. It's turning over and getting spark, fuel and air so I'm not sure where to go from here.
Select the whole response table and add .25. It'll probably start. If it does, go back to the above settings then start retuning the fuel table for the new injectors.
Select the whole response table and add .25. It'll probably start. If it does, go back to the above settings then start retuning the fuel table for the new injectors.
Thanks for the help! Going to try it now.
Where do I even begin tuning the fuel table for the new injectors? Doesn't the long term trim do that automatically?
If you've got that feature, then technically yes, that'll work. It's like any tune though, you ideally want to look at your long term trim table in a few months and see all zeros. Any trim means your fuel table isn't right. My guess is you'll have to drastically change your fuel table for the new injectors. The FF behave much differently than I'm guessing the RC injectors you had before? FM doesn't make injectors.
Like I said, if more response time helps, than you need to adjust your fuel table. Go back to the old dead times, and multiply your fuel table by an arbitrary number, lets say 1.1 for 10% more fuel. Keep going until it idles well. Then divide your current AFR by your desired AFR, to get your final percentage to multiply the fuel table by. Then maybe let long term trims figure it out from there, but a professional tune on a dyno is the real answer.
If you've got that feature, then technically yes, that'll work. It's like any tune though, you ideally want to look at your long term trim table in a few months and see all zeros. Any trim means your fuel table isn't right. My guess is you'll have to drastically change your fuel table for the new injectors. The FF behave much differently than I'm guessing the RC injectors you had before? FM doesn't make injectors.
Like I said, if more response time helps, than you need to adjust your fuel table. Go back to the old dead times, and multiply your fuel table by an arbitrary number, lets say 1.1 for 10% more fuel. Keep going until it idles well. Then divide your current AFR by your desired AFR, to get your final percentage to multiply the fuel table by. Then maybe let long term trims figure it out from there, but a professional tune on a dyno is the real answer.
You rock!!!! Thank you so much and I plan on getting it dyno tuned very soon. Just trying to get it idling and running for now.
The new dead times worked great. Thanks for the advice on the base fuel map Curly! Ended up having to go really rich after a few tries of the 1.1 multiplier on the fuel table didn't work. A 1.5 finally did it! Car idles now at a 9.7 AFR, so I'll fix that asap.
What is an ideal target AFR to use? Currently it is 14.7.
Thanks to Ken Hill for working on this with me too. He gave me an updated map and has been helping get the car running so we can tune it.
Glad it's working, but 9.7 is way too rich. By my previously mentioned rough calculation, you need to take 35% fuel out. Honestly it sounds like these new injectors respond completely different, requiring a completely different fuel table, but it sounds like that's already in your plans. It's going to be fairly undrivable until then.
08-06-2017, 01:11 PM
Car spiking to 4k RPM's on start and can't figure out why
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