Really need help with the last small issue with my 90

[Corvette95]

So this morning...same temps and humidity as yesterday, I wanted to get another video of the cold start before changing idle air and or IAC reset. NOW THE ONLY DIFFERENCE IN TODAY VS YESTERDAY IS THE TWO NEW FUEL PUMPS that I replaced out of frustration, the Airtex pumps had less than 10 miles and 30 minutes of idle on them (they were new). I replaced with over the counter Autozone pumps with a 53 GPM flow. The first ignition cycle of the day gives a 2 or 3 lbs higher readings than the Airtex. Todays video is of the first morning cold start and IAC readings at start up. TODAY IT STARTED FINE, do note the fuel pressure gauge drops into the upper 30's with ignition immediately turned off then rebuilds to 42+ after about 5 seconds? Cut off and restart was fine...long 2-3 seconds crank time which is normal and once fired, ran fine on all subsequent starts. I am NOT going to do anything else today to see if I can repeat a good cold start tomorrow. Fuel pressure with Airtex pumps was within tolerance but on the low side and held pressure. I don't know but maybe was a bad pump- knock on wood. The IAC counts on start up and other of todays cold start parameters can be seen here. Sorry for the shaky video. https://vimeo.com/448080466 Fuel pressure has held steady for 30 minutes now with engine off at 44 psi. Thanks!

[XfireZ51]

One other thought. With the top end taking in more air, the cranking PW may not be enough initially. However, once it starts and then dies, there still may be enough residual fuel so that it, along w second crank, is sufficient to keep motor running for startup

[Corvette95]

Originally Posted by XfireZ51

One other thought. With the top end taking in more air, the cranking PW may not be enough initially. However, once it starts and then dies, there still may be enough residual fuel so that it, along w second crank, is sufficient to keep motor running for startup

I get your point and understand but I wonder if this could be help with a custom tune? I did for the sake of doing it tried cranking in flood mode (full pedal) turned ever but never did start up in ten seconds of cranking in flood mode. It was just a shot in the dark. Aren't you running the MegaSquirt? I look at the parameters need to run that...way over my head.

[XfireZ51]

Not running MS. Using stock ECM. I would suspect flood mode wouldn?t work because I?m suggesting the Crank PW is lean. With second crank attempt, there may be enough fuel in chamber to start motor allowing it to transition from crank mode to startup enrichment. Many times, w short duration shutdown, mine will start at key START almost immediately, and I believe it is due to fuel in the cylinder ready to light up. Anyway, that?s what led me to suggest this other hypothesis.
So yes that is something that could be addressed in tune.

[Corvette95]

Alright....almost 24 hours of sitting. Went and tried to start this morning after a single good start yesterday with new pumps..... nope... cranked,started, chugged and died. I have video of initial fuel pressure, initial Tech1 readings and a IAC reading continuous at the first start - again, sorry for shaky video, only had one chance of getting all the cold condition in one filming...so new pumps were not the answer... https://vimeo.com/448270325 IAC started at 150 went to 118 at aprox 1100 rpms then the stumble it went back to 150. So is the consensus here to adjust the idle air screw on the throttle body to give it a higher idle (turn clockwise) and do an IAC reset and relearn? I am ready to buy a chip, was going to do that anyway. I did order a DataCat so I can record all the parameters on one screen. Suggestions???? Thoughts??? I welcome all and any chip advice.

[Ccmano]

I would do the Minimum Air Adjustment (Throttle idle air screw) there is a good discussion of that in the thread referenced below. Although I use method in the Emissions and Fuel System manual (picture) I would also install a bolt, as outlined in the thread, to make adjustments easier.
https://www.zr1.net/forum/showthread...&highlight=IAC



For datalogging I use either TunerProRt on a laptop or ALDLDroid on an Android tablet. For a chip (tune) Haibeck, Dominic Sorresso or Pete the Greek (can never remember his last name) all in the Chicago area are the go to folks. In Texas, Crossed Flags Performance, Steve Schroeder is also very good. I recommend a custom tune given your issues.
H

[XfireZ51]

Dynomite has my Min Air adjusting procedure documented
here.

http://www.zr1.net/forum/showpost.ph...63&postcount=2

As Hans has pointed out, u?ll want to replace the allen set screw on the TB w a hex head one. GM never intended for the Min Air to be adjusted. At least not the way I have it laid out which comes from my experience doing same and balancing
Xfire TBs.

[Corvette95]

Yes, thanks. I just adjusted my minimum throttle setting approx 1/2 to 3/4 turn. Changed my TPS reading from .54 t 0 .52 . I also did the IAC reset per the exact instructions as above. Requested idle is 675 and the idle is 675-690 with an IAC count of zero. With A/C on rpm request is 710 and the iac is at 18 to 19 counts. I also did a nitrogen smoke test before any of that...zero leaks...smoke only came out the open air lid through the filter. I hooked the smoke to the brake booster vacuum as my source line.

[Corvette95]

So a well known tuner we all know and love, seems to think I need to try a different ECM. Anyone know a source of a ECM or the possibility of loaning me one? Would pay a deposit.

[Corvette95]

For those of you that are following.... this morning..same first start stumble , so today I did the IAC and minimum air adjustment posted by XfireZ71. I moved up the minimum idle as directed with motor restart in closed loop and IAC unplugged to 750 from 675 (XfireZ71) recommended a higher idle but I am starting with this) . Then readjusted the TP sensor that had moved from .54 to .48 due to the min idle adjustment. Locked down the idle. Restarted and revved up to 2000 RPM and cut off. Now I won't know if this helps until a cold start tomorrow. I have about 75 rpm higher base idle with an IAC count of 1 was zero at warm idle. I will post update and may try bumping up idle more tomorrow if no change in starting.