1990 ZR-1 cranks but won't start

[sdickens]

Car is my daily driver. A couple months ago I was Leaving work one day tried to start it, would crank but not start. I had it towed to my*mechanic, they tried to start it, but same issue.
They pushed it into their bay, set it up for diagnostics and then it started right up and every time after that.

Yesterday the issue came back. was out to lunch and when done the car would crank but not start. I got a ride back to the office and end of the day back to my car. It started right up.

Any ideas on what would cause this?

Thanks,

Sam

[tpr60]

I had a s10 blazer that would do the same thing. Ended up being the fuel pump, it was border line on fuel pressure. Would start with 40 psi or above but at 39 psi or below it was a no start.
Good luck.

[scottfab]

Likely primary fuel but strange because even if the engine is warm the secondary pump should allow for a start then quickly you should stall because it shuts down (by design) and the primary is left to supply fuel. The fact that it starts ok when cold also points to primary fuel pump because when cold both pumps run.

You need to attach a fuel pressure gauge then warm it up and watch.

[sdickens]

I don't think it has to do with being cold. The first time it has the issue was after sitting in the parking lot at work the entire day.

I left it there over night, went back the next day and it still would not start. That's when I had it towed, didn't start for the mechanic until after pushing it into his bay.

[CosbySweater]

Could be a temperamental ckp, as stated above though I would check fuel pressure first, had the same problem with a car I was messing with, it would run perfect, then all of a sudden try to start it again and no start, hooked up my laptop and noticed no rpm signal on cranking, replaces the sensor and it's been good ever since

[Schrade]

Could be a temperamental ckp, as stated above though I would check fuel pressure first, had the same problem with a car I was messing with, it would run perfect, then all of a sudden try to start it again and no start, hooked up my laptop and noticed no rpm signal on cranking, replaces the sensor and it's been good ever since

Welcome onto the boards there...

[CosbySweater]

Also, bring a spark plug with you if your daily driving the car still, when it happens pull one wire and check if it's got spark, if it does that immediately cancels out the ckp in theory because that is what is the trigger for the ignition system on these engines iirc

[Hog]

Also, bring a spark plug with you if your daily driving the car still, when it happens pull one wire and check if it's got spark, if it does that immediately cancels out the ckp in theory because that is what is the trigger for the ignition system on these engines iirc
Yes, no ckp signal = no spark. Good idea, its a quick indicator for having spark or not, plus you dont have to pull a plug out of teh head.

Welcome!

peace
Hog

[sdickens]

I had the issue again over the weekend. I had a code reader with me this time and it was code 21 Throttle Position Sensor high. Does this sound like something that would cause this issue? Makes sense if it thinks the car is at full Throttle not to start?

Thanks,

Sam

[scottfab]

The FSM makes no mention of a "no start" if TPS is stuck high.
Dunno......

[CosbySweater]

Well try starting your car with your foot to the floor and see what happens, it could be sharing the same signal wire as the ckp it isn't uncommon for several sensors to share the same signal wire, if you pulled that code you may wanna load test the signal wire and wiggle the harness and check for a open.

[Mystic ZR-1]

What's a ckp?

[CosbySweater]

Crank position sensor, make sure you don't have a temperamental ignition module as well

[POWERBRAKEBOB]

Had this issue for many years, finally, it would not start. I had bypassed the clutch switch years ago. Recently, the pump would not run. I replaced it, no pump running. I replaced all the relays. I bypassed the PASSKEY. I knew the injectors were bad, Changed them. It died one time, and NO crank. Pushed it in. I had installed a hot wire years ago to the solenoid to zap it when no crank. This time, the wire just sparked. SO, I knew the starter was shorted. The shorted starter also burned all the relays, including the f/p, the passkey, and starter enable. Took the plenum off again, looked in the valley....water. The car had been stored for some time, when it had gotten tired. In digging in, I found the valley drain hole was plugged from oil dripping down from the split PCV hose. Drilled out the drain hole at a slant to 1/2" . I took the starter to a friend of mine in the business. It turns out that there is a longer field/armature assy that fits right onto the LT5 starter housing. I had bought a H.D. Ford style starter relay with heavy battery lugs. (those tiny Bosch type relays can not carry current) but did not need it. My car has 253,000 miles on it. I also installed MSD coils on it. This combo spins the engine so fast, that it starts like a carbureted engine. Whamo! I can upgrade your starter to the H.D. armature, if you send it in. I am also working a larger clutch master to stroke the slave farther with less pedal travel.