Hard To Start

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I have a 1997 Chevy Tahoe with a 383 msd digital box new spider injection good fuel pressure, What would make engine hard to start? After starting warms up about 30 seconds runs fine.
Thanks in Advance for any input

 

[kennythewelder]

Could be the fuel pump. You need at least 60 PSI before you start the truck. This is when you turn the key on, but before you try to start the truck. At this point, the ECM cycles the fuel pump relay for 2 seconds. If the PSI is below 60 PSI, the truck will be hard to start. You can rent a fuel pressure tester @ autozone. You buy the test kit, but they give your money back when you return it.

 

[[email protected]]

Thanks

 

[Schurkey]

msd digital box

Does the MSD work properly? How do you know? (They're a high-failure item, as are most MSD ignition coils.)

How fast does the engine crank? Slow cranking = poor compression pressure, hard starting.

What is the battery voltage BEFORE you crank the engine? What is the battery voltage DURING cranking?

 

[[email protected]]

Disconnected MSD and same hard start did that first, Checked compression on all cylinders not long ago. Does not crank slow. Volt gauge says 13v before cranking a little lower when cranking.

 

[89obsSB]

I’d check fuel pressure first. Maybe check timing. I know on the 5.7 vortec with spider injectors you use a scanner and get the timing within -2 +2 at I believe 2000rpm at operating temp. I always try and get as close to zero as possible. But that’s on a stock motor. I don’t know what your setup is.

 

[JeremyNH]

If you had a custom tune for the 383 it may be worth checking the cranking, after start, and warm up power enrichment. I had a 24x conversion done and had a professional tuner do the base and dyno tune based on a 2002 silverado with an LM7. After done the truck ran great warm but had an issue that for the first 90 seconds or so after a dead cold start (as in 8 hours off minimum, any residual warmth in the motor and it wouldn't happen) it would start and idle fine but off ide throttle would result in a very lean condition causing a near stall for about 3 seconds and then surging to power. I bought HP Tuners primarily to have a base tune should the ECM ever fail but also to play with trying to fix the cold warm up condition myself (the tuner said he couldn't replicate it). What I found was that the OL after start and transient warm up enrichment tables were not updated so still had stock LM7 tables which, looking at the numbers, heats up quite a bit faster than an L31 given that it uses a little less enrichment for a significantly shorter duration. Copied in the L31 stock tables along with the warm-up throttle set-points and the cold performance surge went away. If you haven't had a tune it would be worth getting one as I'm certain a 383 won't run the same as an L31. Maybe check the ECT during start-up/warm-up with a scanner as well just to ensure it's giving good signal to the ECM.

 

[[email protected]]

I’d check fuel pressure first. Maybe check timing. I know on the 5.7 vortec with spider injectors you use a scanner and get the timing within -2 +2 at I believe 2000rpm at operating temp. I always try and get as close to zero as possible. But that’s on a stock motor. I don’t know what your setup is.

My Timing is right on even 383 no difference in timing setting. I will keep tring to find problem and let all you know
Thanks

 

[[email protected]]

If you had a custom tune for the 383 it may be worth checking the cranking, after start, and warm up power enrichment. I had a 24x conversion done and had a professional tuner do the base and dyno tune based on a 2002 silverado with an LM7. After done the truck ran great warm but had an issue that for the first 90 seconds or so after a dead cold start (as in 8 hours off minimum, any residual warmth in the motor and it wouldn't happen) it would start and idle fine but off ide throttle would result in a very lean condition causing a near stall for about 3 seconds and then surging to power. I bought HP Tuners primarily to have a base tune should the ECM ever fail but also to play with trying to fix the cold warm up condition myself (the tuner said he couldn't replicate it). What I found was that the OL after start and transient warm up enrichment tables were not updated so still had stock LM7 tables which, looking at the numbers, heats up quite a bit faster than an L31 given that it uses a little less enrichment for a significantly shorter duration. Copied in the L31 stock tables along with the warm-up throttle set-points and the cold performance surge went away. If you haven't had a tune it would be worth getting one as I'm certain a 383 won't run the same as an L31. Maybe check the ECT during start-up/warm-up with a scanner as well just to ensure it's giving good signal to the ECM.

You make a lot of sence with this info Thanks

 

[JeremyNH]

I was looking a bit more at the cranking tables. It looks like the ecm doesn't read the maf during cranking but rather calculates air based on cylinder volume and rpm. When cranking the ecm starts with an initial pulse and in steps increases enrichment as the number of revolutions increases without it receiving a run condition. In your case the cylinder volume is higher than the ecm expects meaning the motor is getting more air than then expected. Consequently the starting mixture is lean and stays that way until enough revolutions have happened with corresponding enrichment steps until you get to the point where you have an afr that supports ignition. So, basically, you need to tune. At least that is my suspicion. You may want to post your problem in the 96+ sub-category stating that you have a 383 with obdsi that starts after excessive cranking. There are people on the forum far more knowledgeable than me that may be able to help you out. Also, I don't have an obdsi. I had an obdsii that I swapped to the 411 ecm but I'm presuming that the tuning philosophy didn't change just the computer that runs it.