Okay, here's the run down.

I have a '96 LT4 with a cold start issue.

The symptoms, it long cranks pretty bad at first start up of the day.

If it's been sitting more than a day, it will cough, spit fuel out of the intake. and backfire from the exhuast. When it does this...after I turn key back from start to on, it will sound like there's a weak combustion and turn the crank a couple of times then either spit and die, or just die. If I hold the throttle down full at these times, it will start after a couple of tries then idle rough for about 30 sec, then she runs as normal.

What's been done thus far...

New fuel pres. regulator after seeing the old one drip fuel. Result, alot less coughing and spitting, but still long crank.

Replaced pcv valve and discovered vacuum leak in it's hose, replaced that but no real effect.

Changed plugs today. The first start up coughed slightly but it started and ran well after a long crank. The old plugs looked pretty good, even for a hotcammed motor running a semi stock tune.

Things that I plan on doing...

Replacing the battery, I know it's due but it tested out still good at Autozone as well as my brother's shop. But it's getting there 4 years old.

Replacing plug wires, they are msd 8.5's but they are also about 4 years old. I have seen no arching however and engine runs well.

Things I've checked...

Fuel pressure, stays at 42 psi ko/eo and remains for more than 30 min after key off.

No sign of leaky injector or injector issues

No sign of coolant in oil or vise versa. Temps and pressures appear normal.

About the motor, Hotcam put in about 2 years ago. GMPP Ls7 lifters also 2 years. GM cap and rotor w/ Hotcam install. Oil pump replaced last summer w/ Melling unit. Oil pressure good. Cat delete, and ECM tuned around it.

The only issue with this motor is this cold start thing. Runs like a bat outta hell otherwise. No knocks or pings, no hesitation, and hates to go slow, ya know?

Could be's????

ICM/Coil? Idle control? MAF? (cleaned Friday) Opti (oh no, do not tell me that, but like I said, runs great after start up)

Any other idea's ?

 

Taking a wild guess here, but with a cold car you need a bit extra fuel to kick it over. Have you changed out the fuel filter? Also wonder if the fuel pump is the problem? Also the injectors may need cleaning professionally.

 

I plan on changing out the fuel filter when I change the battery. So far, since changing the plugs and cleaning the MAF, all it's done is the long crank and not nearly as long as before. I'm also going to run some Techron through the fuel system when I fill up next.

 

Have you checked fuel pressure after it sits and while you're having the long crank issue ?? You have a fuel pump relay and a oil pressure switch which are wired parallel--either circuit will power the fuel pump.
However if the pump relay was bad-- it can cause a long crank time until oil pressure builds causing the oil pres. switch to turn on the fuel pump. Just a thought

 

Perhaps, but I don't really think it's a fuel issue. It tends to want to flood the engine when it happens, so I think it's getting plenty of fuel. Plus Ican hear the usual fuel pump sound when I turn the key. When I had the car in to my brothers shop, we checked the fuel pressure and it was solid, stayed up well past 30 min when off. But then the car had been driven there, so not really the cold start situation.

I got one other suggestion on another forum that mentioned the coolant temp sensor. If indeed it reads colder than true on cold days and the ecm sends extra fuel, this would make perfect sense. There are some warm days coming up, so if goes away completely, that would be a good indicator.

 

Well, last night, I decided to take her for a ride after I got home from work. The car had been sitting for about 8-9 hrs. I first unpluged the MAF just to see what would happen. It turned over immediately, but then shut down immediately as well, repeated this a couple of times, same result. I plugged the MAF back in and same result until I cleared the p0100 code, then it fired right up.

Drove for about an hour, city and highway. No driveability issues what-so-ever, as there hasn't been. But when I pulled out of the store, near the end of the drive I got a p0107 code (manifold absolute pressure/barometric pressure sensor low input) vacuum leak? Which sensor is this? Is it located at the Idle Air control at the TB? Or is it in the MAF itself? I cleared the code and it did not return for the 15-20 min more driving that I did.

 

The MAP sensor is located on the top right (passenger) side of the intake manifold towards the front. It's held in place by two 7mm (IIRC..might be 8mm) bolts and has a green electrical connector. It's hard to miss.

The MAP is used at startup to determine barometric pressure and that factors into how the PCM calculates start-up fuel requirements. The symptoms you describe are typical of a failing MAP sensor. A cheap one from Autozone is ~$45.

 

Well, I changed the MAP sensor, and the tube leading to the sensor looked clogged with the gunk that had been spitting into the intake. No more p0107, thanks for that tip. However the long crank is still there, No spitting or coughing, hasn't done that since the fpr change.

But I have noticed that if I "bump" it for a second and then start it, it pretty much fires right up. I wonder if I might have a leaky injector afterall? What's the best way to check for a slight leak in an injector? Pull it while the systems pressured?