Really need help with the last small issue with my 90

[Corvette95]

My car will hesitate and stumble and die ONE TIME on cold start up...rest of the day, even back to back start up is fine...here is my post and I am adding video with Tech1 data. When my 90 sits overnight or longer, on the very first start of the day it will start immediately rev up to over 1000 rpm stumble down to 600 ish and 9 out of 10 times die. Now, I know what it sounds like BUT....did this before injectors were replaced last week. Did a leak test on the old and new injectors while on rail, old injector on #6 and a tiny drip so I replaced primary and secondary injectors. New fuel pumps (part of a restoration), have fuel pressure gauge on rail (Carters Y, new lines and clamps), with key on pressure goes to 49 then down to 42 and holds during start. Used fuel pump jumper wire, both pumps work and even tried starting with jumper wire to both pumps-no change. Fuel pressure hold steady 2 plus hours after key off- no leak. After first start and stumble or die, restart is perfect...idle to 1100-1200, smooth then idles slowly down to 650 ish smooth idle. TPS is .54 . Throttle body rebuilt by Haibeck last month. IAC count could is around 150 before start up cold then slowly moves down from 50 to single digits. Coolant temp sensors are working both ambient air and water temp. No wire arcing, wires were ohmed good. No vac leaks, secondary runs 2 seconds and holds 4-5 minutes before short cycle. No codes ECM/CCM. Runs perfect other than that. Intake accordian has sleeve to prevent collapse. Engine is low mileage, recently top end port (Pete) and refinish. Stock new Delco air filter with open lid. Just added oil catch can to PCV. Marc Haibeck says he has never seen this and likely could not tune it out. Again, this will happen once...no more that day. Hopefully someone can help and maybe some of the Lotus engineers still here since it is a very low production number with steel half shafts. Replaced cam sensor due to plastic broken when I replaced oil seal. Again, no codes. I would say it sounds like an air leak in the intake but none found. Fuel pressure - every test in the FSM is good. New FPR from Jerry's anyway during restoration. A/C on IAC adjusts idle correctly. See addition post for additional new information about fuel bypass mode....

https://vimeo.com/446827957

[Ccmano]

Have you watched the IAC counts when this happens on a Tech1 or such?
H

[Corvette95]

Hans, the IAC when cold and KOEO, is 150, when it starts it goes to 50 then progressively lower to single digits then 0. What I have been researching is on start up the knock sensor retards timing 3 degress as it shows a start up only spark knock after that, I cannot get any knock at any rpm. Now according to the FSM, the car starts on backup fuel below 400 RPM. after start up spark advance is steady at +8 degrees, throttle blip will lower advance for split second then advance it up to teens and lower twenties. Car runs like a top after first start. NOW INTERESTING THING I FOUND is if I select backup fuel when it is running fine hot or cold it runs like crap on backup fuel...that could be something. Fuel pressure at first ignition cycles runs both new pumps to upper 40's then bleeds off to low 40's, start up fuel pressure drop to 39-40 for split second during crank revolutions then back up to low 40's. If I cut the car off pressure holds in 40's for 2 hours. Now the FSM says both pump should re-energize on new key cycle with coolant temp under 100 + degrees - don't remember exact temp both pump quit being energized and only the primary energizes when warm but a new key cycle with coolant temp under 100 will only activate primary, but either way fuel pressure is over 40. Map sensor is giving good info. I reset the fuel block learn and it runs at 118/119 and has a short term learn factor of 5 so it is rich but rich should make start easier? No codes at all. I would appreciate help on this matter as I have researched every avenue I know of. Anyone know if a quick measure of spark knock on start up is normal?

[grahambehan]

I saw your video showing -3 degrees of spark on your initial start up, there is a rudimentary form of cat light off spark if the car is started within certain coolant Temps, emission territory. This table has a max authority off -10 degrees. Does your calibration have this addressed?

Graham

[Paul Workman]

I wish I could add something to the discussion on the 90. Your data on the Tech-1 is very similar to my results: nothing different enough to mention, even.

However, my wife's 91 acts exactly the same way on first startup of the day, UNLESS I blip the throttle as it stumbles down to idle. (Oh, and the 91 also has a elevated idle when it fires, but more like 1400 to 1500 rpm (instead of 1900 ish rpm for 4-5 second for the 90) before settling after 2-3 seconds.)

Other than that, it runs like a top. So, now I anticipate the stall on first start of the day, and a quick blip of the throttle is all it takes to avoid it. After that and on subsequent starts during the remainder of the day, she fires up almost instantly - with gusto (Pete's cams in her car).

I get no codes, and because that blip is all it takes to cross over the stall, I just shrug and never give it another thought.

Your mileage may vary!

P.

[Corvette95]

So this morning, pulled the wire from the knock sensor before starting so no retard on startup...no difference. First crank engine fired up to 1000+ rpm stumble then dies..all with 40 psi for fuel pressure. Verified MAP sensor was giving correct readings before start up. Second start up fine. Now, on cold start up Tech 1 shows desired engine speed 3187 until first engine revolution then changes to 875 or so. I don't know if that is something or not.. It will repeat the same desired RPM on restart as well and it starts and runs fine. OK, new detail this morning. If I set to backup fuel on tech 1 the fuel pressure bounces from 40-50 (see video https://vimeo.com/447820587 ) . It will also pop/small backfire on heavy throttle blip on backup fuel only) . Any ideas?? Graham.... low mileage 90 with stock calibration. Recently bought and have restored..only mods were top end porting by Pete, open air lid, and cat back exhaust. When on closed loop it shows a BLM of 118 with short term trim of 128 both banks.

[Corvette95]

I wouldn't think plug wires or coils since it runs so well after the first time and no codes. I did not replace the coils,as they were not original. I did replace the #8 wire only..other ohmed good.

[Corvette95]

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[Ccmano]

What I'm interested in is what the IAC is doing when it stalls. Is it showing a reading or is it at zero? I prefer to analyze things from the perspective of "Accams Razor", looking at the simple things which are more likely before we get carried away with a multitude of complexity.
H

[grahambehan]

Prev post said 150 iac, park position prior to start, 50 counts at start, dropping to single digits/0 counts.