Well I have an interesting problem 87 L98 no real mods, car has been off road for about 1 ½ years. Started driving it last week it’s very hard starting when hot after it’s been sitting for ½ hour or more if it starts at all let it sit a few hours’ starts up. Let me add that I have new fuel pump & FPR, 40 lbs pressure, have checked for leaking injectors (Bosh lll 2 years old ) cold start injector not leaking, all plugs dry and normal. New Battery NO CODES flashes 12 as it should. Fuel tests per FSM normal once car starts it runs great no issues, also new IAC. Have put about 300 miles on car just would like it to restart as it should. I am leaning electrical but have great spark when it’s not starting .
Any thoughts or help would be greatly appreciated . Thanks

 

Sounds like you are having starter issues. Does the car start fine when it's cold? Is it turning over slowly when it's hot?

 

per FSM, try the flooded engine start, pedal to the floor. verify timing at 6 deg, with ecm disconnected, of course. sounds like too rich, but not as likely with new injectors. coolant temp sensor also affects the A/F ratio -not the gage sensor, the one near the IAC. if it indicates a cold engine, will enrich the ratio. FSM tells how to check resistance but is hard to get to.
not sure it's electrical, since you have spark. ign timing would affect it all the time, but...

you have verified that the injectors are getting the signal, with a noid light or test light? that would make it "lean," of course, and is also unlikely. but, it's a Corvette!: lol:

 

strong spark throws me, otherwise I would say weak coil.

 

I would bet it needs more cranking pw vs coolant temp in the tune due to the Bosch III injectors and the ethanol content of today's fuel supply.

You can try raising fuel pressure as a test to see if it helps, but plan on retuning for the injectors and fuel.

If in a pinch, pull the vacuum line off of the regulator to temporarily boost fuel pressure, and plug it back in once car starts.

 

another member had the same issues.....and he tried endless solutions. Nothing worked. Nada. Finally he inadvertently broke the temperature sensor; replaced with new and, viola! starting issues fixed. Theory was that the old sensor was sending incorrect info to computer and the computer thought the engine was hot all the time, even when cold, and adjusted the timing accordingly; i.e. cold engine, timing incorrectly set for hot start = no start for cold engine, but always started easily once engine was warmed up.

 

I have an 1985 that I always turn on the key and listen for fuel pump relay to click off. Only then do I turn the ignition switch to start.

Either cold or hot, the engine starts immediately.

I do the same for the 1996 LT4 and it starts immediately.

 

Coolent temp sensor is new, starter cranks fine very strong,hot or cold, Bosch lll are not affected by ethanol content in fuel, explaine why I would need more then 42lb of fuel pressure?. Car has had Bosch lll for over 7 years without missing a beat. Have tried the flooded engine start nothing. I will have to see the electrical route of the ICM to the ECM to see if the impluse could be cut to the injectors when I get home to my FSM

 

if not rich, then lean, perhaps. if my memory is right, the ECM controls timing, but not spark, so it could be the problem, since you have spark. if you are sure an injector is not leaking. the noid light will tell you.
watch for the tach needle bouncing during crank, meaning the dist is sending pulses to the ecm. it probably is, since you have spark, which comes from the pickup coil.

 

The premise is that it is too lean to start under the conditions.

Fuel containing ethanol requires more mass/volume than gasoline and therefore requires a larger injector pulse width to deliver the appropriate amount of fuel to start and run properly.

Different fuel injectors also have different response characteristics and may require different offset values vs voltage to compensate for the injectors' opening time delay. Not enough offset for the injector and the actual injector opening time is reduced which reduces the effective flow for a give pulse duration

As coolant temperature is increased, the crank pw gets smaller. If the pulse (that worked on a new car in 1987) is too small for the current injectors/fuel/engine/car/environmental conditions....no start. You can't make it richer without introducing more fuel by some external means.

Increasing fuel pressure is something you can do to crudely test the lean premise by enrichening the mixture. If this helps, then it suggests you need more cranking fuel pw and/or more injector offset for your specific combination.

Here's an example crank fuel pw vs coolant temp table for reference:

;---------------------------------------------
; Crank Fuel vs Coolant Temp.
;
; Table = Msec * (65.536 * 256) / LC372
;---------------------------------------------
ORG $0374 ; msec PW COOL Deg c
;-----------------------------
LC374: FCB 230 ; 89.8 -40
FCB 205 ; 80.0 -28
FCB 77 ; 30.1 -16
FCB 51 ; 19.9 -4
FCB 33 ; 12.9 8
FCB 23 ; 8.9 20
FCB 20 ; 7.8 32
FCB 19 ; 7.4 44
FCB 18 ; 7.0 56
FCB 17 ; 6.6 68
FCB 14 ; 5.5 80
FCB 14 ; 5.5 92
FCB 16 ; 6.3 104
LC381: FCB 20 ; 7.8 116
;------------------------------------------------------

 

Possibly the coil. If you pull a spark plug wire and hold it next to the spark plug and have someone else crank when this is happening, what color is the arc?

 

As the OP states in his 1st post

"have great spark when it’s not starting ".

 

Which sensor? intake or PS block? The later "talks" to the ECM.

Any correlation between part swaps and the problem?

Because 300 miles since relaunch, I will assume gas isn't old.

 

I would ohm check injectors when engine warm first, then fuel pressure with engine hot with key on, then base timing. One other thing you may check is if the oil pressure switch is showing signs of leaking.

 

Was that driving 300 miles on 1 1/2 year old gas?

 

l98tpi, oil pressure switch does not affect starting unless the FP relay is out of the circuit. it is backup only. even then, it would only delay starting until the oil pressure reaches about 4 lbs. he has fuel pressure, spark.

joe.

 

Coolent temp sensor in intake, Gas has always been fresh even though I was not driving car I was starting it a few times a month. When hot I still get 40+ lbs at rail, no leaking at oil switch. I will have some time to get into the dizzy tomorrow. If the ohms were off on injectors it would affect the car after driving 30 or so miles which I am doing although I have not ohm checked them runs fine at operating temps I have even run it up to 240* to see if there would be a shut down. I'm sure it's just something off that I have missed, time to open a beer and the FSM

 

Before I did anything else I'd recheck that fuel pressure and watch how far and how fast it drops. Sorry, but it really sounds like a leaky injector(s).

 

Possibly a leaking diaphragm at the FPR.. do you get any black smoke on start up?

 

Just a short up date yesterday I changed out the damper which was causing fast bleed off in the fuel line, now pressure holds 4 hours before bleed off to around zero. I also had a spare ICM here so I switched that out the old one had no dielectric grease under it, Ohm check injectors hot all checked out around 17 .1 - 17.5 I did find a bad connector on injector harness was loose no change on no start. Yesterday I also replaced cap and rotor was about 7 years old . I still have to reset IAC and base idle, will get some new plugs also. Runs great but still hard to start when hot after sitting. I just checked spark again on no start color is orange blue.