What causes hard starting?
 

Hey all. I've got a '91 Chevy Camaro Z28 with 5.7 tpi motor. I have been experiencing hard starting after the car sits after 24 hrs. When I start the car it takes approximately four seconds for it before it cranks over. When I purchased the car ten years ago, the car started right away. I had the fuel pressure regulator replaced a year ago and another part that is kind hard to describe but here goes- it is located on the passenger side adjacent to the heater check valve and has two sensors with one diaphram on each side and has rubber hoses connected to it that snake to the air injectors on the exhaust manifolds. What do you guys think?

That'd be your AIR diverter valve. That shouldn't affect starting at all.

I have a hard start problem as well. I don't know if its a tired starter, not enough fuel, too much fuel (maybe leaky injectors?), too much spark, not enough spark, etc.

Seems to be common on older TPI cars. Had three and they all were the same. This 88 I have now, I have replaced the whole fuel system, even the injectors. Wiring diagram shows no crank signal for cold start enrichment. Complete ignition tune up with module and coil. Runs great, good gas mileage, but long crank time on first start. Port injected engine should start quick I'd think. I give up.

So you don't have any problems throught the day?take your battery to your local parts store and have them test it for you.

So you don't have any problems throught the day?it could be a weak starter or starter solinoid or it could be the battery.take the battery to your local parts store and have them test it for you.you could do the same with the starter and have them pull a new one off the shelf and have them test it and compare the two.

When you say "4 seconds to crank over", do you mean before the engine fires and runs? i/e does the engine spin good, but just doesn't start, or does the engine spin slowly before starting?

Exact same as my car. I haven't replaced the fuel system though. I need to check my fuel pressure and I think I could possibly have a leaky injector or two. I have new 24#s here but I'm waiting til I get the LT1 intake ready to install those.

Either way, I get great gas mileage, and she runs great once running. I can turn it off and turn it back on and it fires right up *instantly*.

Haven't checked my base timing though either. Interestingly enough, some days it will start right up fine though. I'm trying to figure out if there's a correlation between coolant temp and starting effort to see if I can change one of the startup tables in the PROM (timing vs. temp, fuel vs. temp, etc.).

Re: What causes hard starting?
 

Any updates?

Re: What causes hard starting?
 

Whoa, eleven years later. No change with my TPI. I did put an LED across the injectors, they fire right off, still no start for 20 revs or so. Every thing checks out, just no fire. Really weird. Thought about putting a pushbutton switch on each bank of injectors to put a ground connection to them, full open, see if that does the trick. Not sure what that would do to the ECM though. It operates the injectors by controlling the grounding pulses.

Re: What causes hard starting?
 

One area that will cause long starts after the car has sat for awhile is an inoperative fuel pump relay. When the fuel pump relay goes bad, powering the pump is left to the oil pressure/fuel pump backup switch. After several cranks, the oil pressure increases to a point where the switch closes and the fuel pump is energized. The fuel pump backup switch and fuel pump relay are hooked up in parallel.

Re: What causes hard starting?
 

You can probably hear the fuel pump come on when you first turn the key on (just to run not start.) Otherwise you could put a test light on it to test the relay. It should run for 3-4 sec when you first key on. This test will rule out if your relay is the problem.

Re: What causes hard starting?
 

it was my fuel pump