Really need help with the last small issue with my 90 - ZR-1 Net Registry Forums

Corvette95 · 08-12-2020

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

08-12-2020	#1
Corvette95 Join Date: Jan 2006 Location: Decatur, AL Posts: 1,121	Really need help with the last small issue with my 90 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 Last edited by Corvette95; 08-14-2020 at 08:51 AM.