Here's the backstory on the car.

Bought April 1 2015. 80.5k miles. Have receipts for new (OEM) motor (old motor lost compression,) clutch, misc stuff installed at 78k miles by Mazda dealer. Car drives back from 5 hour trip fine, only issue is a bit of a stutter around 3300-3800 rpm. (occasionally) Go to fire up the car next day after I bring it back, it cranks but wont fire up.

Shipped to mechanic (1). He fixes some stuff, boost sensor, new fuel filter, plugs, oil, sorted out some vac lines, etc. Car still won't run 100%. Every time I drive the vehicle, it runs great, but when I shut the car off and try to fire it back up it will crank but not fire. Car is then shipped to a rotary tech (mechanic 2) working out of his house. He fixed a clutch safety switch and gave the car back (while the car was being towed the clutch safety switch failed, he thought that was the only problem.) Went to get the car, I fired up the car, drove 15 minutes to get gas. Put gas in, drove it to get lunch. On the highway in 5th gear at cruising speed the car shut off. I slowed down, put it in 2nd and bump started it. Car ran fine for the next few miles. I shut the car off and when I came back out from lunch, same thing. Cranks but wont fire.

Back to techs house . He has it idling for a while, and was checking fuel pressure. Car stalls and shows 28 psi fuel pressure. He orders a walboro and puts it in, and supposedly had the car idling saturday and sunday up to operating temp. I went last night to grab the car for a test drive and it fired up, but stalled after about 1-2 mins of idling. Car would crank, but not fire up.

1. I cant remember if it was compression tested, but I champagne tested it and no bubbles appeared. I'd find it very hard to believe compression is bad. Brand new motor, and when the car is running it pulls incredibly strong.

2. Due to taking FOREVER (mechanic 2 had car for months and months,) I'm going to try and do some small stuff myself. After research, I'm thinking the stumbling issue could be bad grounds.

3. The longer I've have the car the quicker it wants to stall after cold starts. It's acting like my corvette did with a bad fuel filter. After research I'm seeing similar issues with FPR, fuel pump relay, grounds, etc.

Based on the above knowledge, where would you guys look first? I have very mechanically inclined friends and I'd like to try and diagnose myself before getting it shipped 1hr+ to a reputable shop.

 

I'm gonna take a quick guess at this. It might be your crank angle sensor. If your tach doesn't bounce when you crank it, than it's your crank angle sensor. I searched through several hundred threads on this forum the 2nd week I bought my FD and had the cranking/not firing up problem. Love this forum!

 

Intermittent problems like this are typically electrical, I have had many cars come in that have faulty relays that stop working once they get hot. I would start with the EGI relay. If the fuel pump is not priming when you turn the key forward then look at the Fuel pump relay.