1997 5.7 Vortec intermitant slow start

Steven_R · April 24, 2020

I have a 1997 5.7 Vortec with the CSFI system. It has 130k miles.

Symptoms:
It is sometimes hard to start when cold. The engine turns over fine, but only starts after cranking for a variable amount of time. No cel and no codes. Once it has started, it runs fine and it will start easily later that day. This was happening infrequently, but now occurs most days.

Recent parts:
About six months ago I gave it new plugs, wires, cap and rotor. The plugs looked old, but consistent and no oil fouling.

New fuel pump and filter about four months ago.
Used AC Delco parts.

I have done some testing:

Fuel pressure is good - 60 psi when pump is on. It holds pressure for a long time after ignition is turned off. Pump comes on for a few seconds when ignition is turned on.
Removed and checked EGR - no blockage. Also the EGR stays cold when the engine first starts.
I believe it has good spark. I tested three spark plug wires with a timing light during a no-start situation.
I used a scanner and checked some live data during a no-start, but noticed nothing.
Used the scanner to check TPS and ECT - both good. (GM shop manual says to check those two in "Engine Cranks but Does Not Run" procedure)

I would like to figure this out and not just throw parts at it. Any help would be appreciated.

Edited April 25, 2020 by Steven_R

Steven_R · April 24, 2020

Here are some possible next steps I am considering:

1) Measure the resistance of the injectors.

2) Test the injector wiring with a noid light.

The manual said to use a simple unpowered 12v probe. I did and could not see anything, even with the engine working, so I will need to buy a noid light to test.

3) Check any of the many sensors: MAF, IAC, CPS, etc.

Again, any help would be appreciated.

east3021 · April 25, 2020

Fuel pressure is good - 60 psi when pump is on, holds pressure for a long time.

Can you clarify - With ignition off, does it hold this pressure or drop off quickly? There is a section in the manual for fuel pressure testing which covers how to isolate the supply and return in diagnosing leaks at the injectors, regulator or pump.

Are the injectors/regulator original?

Does the ECT read a normal temp at cold start (around ambient) and stops at around 195 (or around your thermostat setpoint)? Usually, you’ll see a hard hot start when when these flake out, but holding the gas to the floor puts it in ‘clear flood’ mode and is a workaround. This stops injector flow.

Steven_R · April 25, 2020

1 hour ago, east3021 said:

Can you clarify - With ignition off, does it hold this pressure or drop off quickly?

It holds pressure for a long time after the ignition is turned off. (I edited the original post for clarity)

The injectors/regulators are original. 130k miles.

The ECT reads the correct temperature before starting. I haven't done much testing once the engine starts.

Also I have been thinking that the injectors are good because 1) no leaks and 2) good performance after first start of the day. Is this correct?

OldGuy96 · April 25, 2020

I had a 96 Silverado that exhibited the same symptoms after replacing the plugs, cap and rotor. I tested everything I could, and then finally, in frustration, took it to a factory trained Chevy mechanic.

When I explained all the things I'd replaced and tested, he asked me what brand cap and rotor I had used. I told him I'd bought a reputable brand (don't recall which one now) cap and rotor fro the local parts store. He told me to go to the dealer and buy a factory OEM set and install it. I did as he instructed, and my hard start problems went away instantly.

He told me that it is very common for aftermarket ignition parts to cause starting probems with that engine. Since then, I've talked to several other mechanics that confirmed what he told me.

I can't explain it, but I know that it worked for me.

diyer2 · April 25, 2020

I used only Accel caps and rotors on my 93 5.7.

Copper contacts instead of aluminum.

$35.

Lasted longer than the aluminum and better conductivity IMO.

Steven_R · April 25, 2020

First, thank you all for you advice.

east3021 - I have had several other people suspect the ECT besides you, so I replaced it. I haven't tried to start it cold since then, but will today. I don't think it is that, but would like to eliminate a "suspicious character".

oldguy96 - All the parts are either ACDELCO GM original equipment or ACDELCO professional series except the Champion 9404 Iridium. I have had good results with these brands. I hadn't thought about the cap and rotor. I will take off and inspect the cap. I will be looking at the van again this morning.

riverbanks · April 25, 2020

Try running some techron cleaner in the gas tank,you might have bad spray pattern on a couple poppets,so, when it starts,is it rich or lean?black tailpipe or clean?another item to try, disconnect MAF electric connection,see if it starts better

east3021 · April 25, 2020

It holds pressure for a long time after the ignition is turned off. (I edited the original post for clarity)

The injectors/regulators are original. 130k miles.

The ECT reads the correct temperature before starting. I haven't done much testing once the engine starts.

Also I have been thinking that the injectors are good because 1) no leaks and 2) good performance after first start of the day. Is this correct?

Just a guess, but maybe you have a regulator or injector(s) slowly leaking the pressure down. Maybe leave the pressure gauge on overnight and see what it reads in the morning.

You can also rig up a test kit to verify, use ball valves to isolate the supply and return lines at the fuel filter. The test procedure for that is in the factory manual, let me know if you need a link to it.

Are any cylinders showing misfire counts in the scanner?

When you start it and know it’s going to be difficult, does holding the ignition on for a few seconds help (allowing the pump more time to run before trying to crank)?

Steven_R · April 25, 2020

2 hours ago, riverbanks said:

Try running some techron cleaner in the gas tank,you might have bad spray pattern on a couple poppets,so, when it starts,is it rich or lean?black tailpipe or clean?another item to try, disconnect MAF electric connection,see if it starts better

Disconnected MAF. No change. The car has not started this morning (i.e. it's getting worse). The tailpipe looks normal (grayish black). I wipe my finger on the inside of it and get only a little dry grey powder. I will try fuel injector cleaner if it starts.

riverbanks · April 25, 2020

Hmm,try disconnecting c.t.s,that will take it full rich,if no improvement,go back to ignition,weak connection on coil?and as mentioned,a cheap distributor cap can cause problems,what about,use a spare spark plug and look for blue spark

east3021 · April 25, 2020

Still getting 60-66 psi at the fuel test connection?

I’d agree that checking for spark would be in order now that it isn’t starting at all.

Steven_R · April 25, 2020

More testing...

All the injectors measure 11.6 ohms to 11.9 ohms resistance. I think that means there is no electrical problem there. (Not to say one or more might be stuck).

Steven_R · April 25, 2020

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?