ever since it got cold out, my car was pretty hard starting...it warmed up a little, and its not as hard to start now, but sometimes it just doesnt want to crank over. i found that if i turn the key on and off twice to prime the fuel pump, it will start fine, but when it does start, instead of idling around 1100 where it is programmed to idle, it will struggle to reach that idle at around 600-700rpms, and then after a few seconds finally get up to 1100rpms. but thats not all. when i go to move the car, especially when in reverse, and then pop it into neutral coming to a stop, the car will sometimes bog down a little, or even stall out completely. when it stalls out completely, its very hard to get to crank over and start up again, and only seems to work when i pump the gas pedal while turning the key, and then when it starts up, puffs a little smoke outta the back of the exhaust and smells like alot of unburnt fuel...its been doing this for almost a week now, and has never done it before...any ideas or help is greatly appreciated!!!

edit: i know there is a small exhaust leak near the y pipe somewhere, but not enough to throw off O2 readings, at least i dont think so; the injectors are new since the engine build less than a year ago and are 42# custom built, new stock FPR, new in-tank walbro 255 lph fuel pump, new fuel filter within last month or two, have MSD digi 6+ box, new MSD 8.5mm wires, havent pulled spark plugs yet to check anything, and havent ruled out the opti, but its no more than a year old...also, does not feel like a miss because it still pulls pretty hard through the rpms when i get on it

 

Check what the coolant temp sensor for the PCM is reading. If its giving the PCM the wrong temp, it will affect idle speed and can cause hard starting.

Might also want to check the fuel pressure, and how fast it drops off when the engine is shut down. If the injectors are leaking, its going to lose fuel pressure quickly, and will require that you hold the accel pedal on the floor in order to start it, putting the PCM in "clear flood mode". "Pumping" the gas does nothing, except alter the amount of air the engine is getting.

 

what do i need to check the temp the PCM is reading from the sensor?? i dont have any datalogging software, just and obd2 scanner for codes...would the easiest thing be to just replace it with a new temp sensor since they arent that expensive?? i just dont want to go throwing parts at it tho...
thanks for the info btw..good to know

 

You either need a data logger, or a full scanner (not just a code reader) that can read the various sensors. If you don't have access to a scanner, check the sensor per Shoebox's guidelines:

http://shbox.com/1/4th_gen_tech2.html#ect

I wouldn't start replacing things until you checked the other possibilities. Check the fuel pressure. That's just as likely to be the source of your problem.

 

ok tomorrow i will check out the fuel pressure and the ECT sensor...what should the fuel pressure read? and if it is reading low, what would that mean, given my symptoms?

also, could a vacuum leak be causing my problems as well? if so, where should i look?

 

#1 make sure you ETC temp sensor is working as stated above.. Your fuel pressure after clicking the key on should be over 40# and hold it for quite a long time, (mine holds for hours) if it hits 40 then drops off fast then defective regulator, fuel pump check valve or leaking injector could be problem. If it does not hit 40 then most likely bad fuel pump, could be filter but with low/no volume flow when stopped it's a long-shot. You symptoms sound like it's flooding since you need to open TB to get it started and you smell fuel after it kicks over. In OBD1 we have a 'Prime Pulse Width Vs Coolant Temp' table that controls the cranking pulse width of the injectors. The OBD2 should have something similar. With the 42# custom injectors and cold starting temps lately using the cranking injector pulse widths could be over fueling (flooding) during cranking. You should ask you tuner about that to make sure the lower temp settings are correct ?

 

hooked up a fuel pressure gauge to the schrader valve, and with the following situations, i have the corresponding fuel pressure:
Key on/Engine off = 40 psi
Key on/Engine on = 42 psi
Key off/Engine off (after running) = instantly dropped to 35 psi and held there.

also, replaced the engine coolant temp sensor in the water pump, and car did not bog down or stall at all. it seems that the problem may have been fixed, but not sure as i haven't had the opportunity to take it for a longer drive yet. aside from that, are the fuel pressure numbers normal??

 

Yes that seems normal.At least your car starts!I,m going to hook up a gauge &chk. my pressure b/c my car cranks but doesn,t start.I,ve had symptoms of weak pump for yrs. 7 now it maybe dead

 

haha i think the ECT may have fixed it, but not sure because i havent had it running long and the only driving i did was to move it from one driveway to another, but it didnt bog down or act like it wanted to stall out, which is an improvement...
i have all new components, including a new 255lph fuel pump that i put in with the engine...

 

ok my problem is not solved...it seemed ok yesterday, but like i said, i didn't drive it anywhere except between two driveways. took it to work and back today, and when i start it up, it wants to bog down and stall out again. after it is warmed up however, it still idles low and seems like it wants to bog down, but always catches around 800rpms and pulls itself back up to idle between 1000-1100rpms where it should. it doesnt seem weak at all in acceleration, but on decel, the idle used to hang around 1300-1400rpms until coming to a stop. now, it drops to 1000rpms and when coming to a stop, dips to about 800-900rpms and then back to where it should be. any ideas?? fuel pressure checked out fine, and the ECT is brand new now.

 

dead cylinder?

 

no way, i can still roast the tires pretty smoothly...definitely not a dead cylinder

 

need help with this....the car is a daily driver, and its not serving that purpose too well right now...lol

EDIT: forgot to mention, as i was turning into my parking spot at work today, the car stalled out again. i had to hold the gas pedal to the floor to start the car again...

 

Could be a problem with the idle air control (IAC) motor. That's what controls the idle air, and prevents the engine from stalling. With a scanner, you can watch how the IAC system responds to the incorrect idle speed. It won't tell you whether the IAC motor is working, or if the idle air passages are dirty, but it will tell you if the PCM is responing to the incorrect idle by trying to change the IAC motor position (counts).

It isn't unusual to have idle air problems with the aftermarket throttle bodies.

 

well about a month or so ago, i had idle air problems, i now have a brand new TPS and IAC, both were dialed in perfectly along with the throttle blades themselves. is it possible that the stop screw for the throttle blades could have just become slightly closed more due to engine vibration? it has been adjusted several times...