I have a 87 trans am i swapped an lt1 into. The lt1 has the lt4 hotcam, new springs, 1.6 roller tip rockers, shorty headers, 3inch exhaust (no cat), lt1 knock module (planning on using the LT4 but i show no knocks while running) and a 80-90psi new fuel pump on 93 octane. Atm i have the mass air flow disconnected. Sometimes the car will start right up, and seem to idle fine. Sometimes it's a pain in the *** to get going. And recently it's been almost impossible. I can crank and crank on it. It'll sputter like it wants to but wont go. Seems to me like the timing is off. If i leave the car for an hour or so, it'll be A LOT easier to start. (maybe fouling the plugs?). So i hooked my scanner up.

Is it normal for it to detect knock while cranking? While cranking im showing literally thousands of knocks, and up to 13 degrees of retard (im guessing the culprit for hard starting). Once it starts though, no knock at all. But it does seem to keep 2.3-2.5 degrees of retard for a few mins before dropping it. My O2's are showing very rich at 939 mv. Also im showing only 65-69 KPA MAP, which isnt that like only 9.5 PSI of vacuum? seems low. All vacuum ports are plugged or hooked up.

See attached datamaster log. This log took place over many hours. There's a bunch of starting attempts in here, and a running once at the end with revs.

If anyone has any ideas please share :x

Thanks!

 

Is your knock sensor matched to your PCM?

 

Came on the engine from the yard. I'm thinking about replacing the one near the starter and seeing what happens. Or just unplugging it for that matter.

 

Unplugging them should let you see if the problem is with the starting

 

unplugged both, no dice. Still stutters, if i give it like 1/8th throttle it'll start, but dosnt seem to like it.

 

o2 sensors do not come in on start.are you sure you have the tps sensor set right. do you have fouled plugs from running to rich?

 

TPS is 0.57V at idle. Perfect. Fouled plugs is a possibility

 

I'm seeing a lot of trouble codes pop up. Almost all of them seem to be electrical and your voltage doesn't look very good. If you click on the "DTC error" that is highlighted in red, it will open a window with all the codes.

-I never see voltage go above 12V and sometime see 6V, 9V, 11V, all over the place. When the car is running, it should have 14.4V. Is the alternator wired up right? -Is the resistor added or pin moved on the alternator connector? Is the alternator good?

-The Coolant temp sensor. In the beginning of the log it starts at 20 degrees Celcius then climbs a little bit, then drops and stays at -40C, then jumps to 26C and stays there. The sensor could be bad or have an intermediate wire connection there.

-Intake Air Temp sensor never changes and stays at -40F. Its either not wired up or bad.

-One of the O2's never change values. Could be bad or not wired up.

-I'm seeing a 4000ppm VSS circuit fault but that won't effect how the engine runs at idle.

-Also never goes into closed loop but if I remember right, the mass air flow sensor needs to be hooked up for that.

 

Could be something going on with fuel too on top of the electrical. The stock regulator only runs at 40-ish psi. Check fuel pressure and see what's going on there. Also, if the pressure drops instantly or somewhat quickly after the car is shut off then could have a leaky injector, or leak in the line.

 

I would check grounds, make sure all of the ground straps are attached, should be a total of two, one on the back of the engine bolted with the transmission to engine bolts, and one at the coil that I attached to the frame rail on the driver side.

2 knock sensors? Mine only has 1 and I pulled the motor out of the car myself, that's on the passenger side at the in the middle of the block.