1997 5.7 Vortec intermitant slow start

[Steven_R]

All right, It has no spark. I was previously testing with the timing light and that is apparently not as good of a test. The timing light still flashes occasionally, but the spark plug test shows nothing. I did the spark plug style test on a running 7.4 (almost identical ignition) and the plug had a bright steady spark. So I think we have a good idea of the problem. The manual has a 3 page diag procedure that looks pretty detailed and systematic. I will try that and give you an update.

 

[riverbanks]

Ohms test the coil,do it cold and then after some engine cranking, probably show a difference

[east3021]

There are no misfires in the history.
 
I said that the fuel pressure stays for a long time, I meant many minutes, not hours. I left the gauge on after testing and it was down to about 10 PSI at the end of the day.
Should it stay pressurized for a whole day?

I’ve never found a good answer for that. The manual just says it’s regulated to 60-66 psi with engine off (no vacuum) based on the spring pressure of the regulator.

I suppose it would drop as system and ambient temperature dropped, but think that most look at a quick drop over a few minutes as a sign of a leak somewhere.

In case it helps, here’s a nice write up with photos on testing the ignition system...


https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/ignition-misfire-diagnostic-tests-3

[Steven_R]

Status:

I tested yesterday and found the rotor had broken. I replaced the rotor and it started right up. It also started right up this morning, so I think that it is fixed.  I will leave it be  an see how it starts after sitting for 24 hours. I bought some techron fuel injector cleaner and will use that as soon as I am sure the main problem is fixed.

 

BTW, the 3 page diag procedure in the manual that I used is pretty smart. It divides the system in half to narrow the problem to one part. I does however tend use specialty tools when common tools would do just fine.

 

 

Questions:

23 hours ago, riverbanks said:

black tailpipe or clean?

Riverbanks - what can we learn from the tailpipe condition?

 

Also, it has been suggested to me that replacing the spider injectors with the MFI conversion kit from ACDELCO would help both performance and economy. Is it really that much of an improvement over the original system?

 

[east3021]

 

Also, it has been suggested to me that replacing the spider injectors with the MFI conversion kit from ACDELCO would help both performance and economy. Is it really that much of an improvement over the original system?

 

 

Glad you got it sorted out and thanks for updating your thread.

 

I have two 98 models, one a Z71 and the other a two door Tahoe. I did the MPFI on both while doing the intake gaskets.

 

I noticed a better throttle response in the truck but no noticeable difference in the Tahoe. I suspect that most of the improvements noted are in comparison with stock injectors that were in marginal condition. You don’t tend to notice a slow decline in performance until the bad part is replaced.

 

I’ve usually averaged 11-12 mpg in both of these. The injectors made no difference there in my case, but others may have different experiences.

[riverbanks]

Tailpipe condition, just my go-to,like, when someone says,the engine sputters,I don't know if it's flooding with fuel or starving for fuel, tailpipe gives a pretty good indicator