med1212

I have 60 lbs at the fuel rail and it will start on starting fluid but won't run. How do I test the injectors and/ or the computer?

MT-2500

Go easy on starting fluid.
Carb cleaner is safer.
You should have 60/66
60 is borderline or 5 lbs low on cold cranking.
You need the full fuel pressure for a injector to squirt fuel on a cold start.
Pinch off return line and it should jump to 75-85 or little more.
Check injectors pulse and pcm with a scanner.
Or a node light can be used to check injector pulse.
Most parts place have them.
MT

__________________
Remember proper testing gives us the answer to many problems.
MT

drew300

With my '97, GM said 'minimum 60" psi.
I had 59 psi on the guage I borrowed, and it wouldn't start, accept with starting fluid, but then ran fine. With a new fuel pump, it's fixed, but I returned the guage before I got a repaired reading.

MT-2500

Drew300
10-4 on that.
1 lb to low and the injectors will not squirt on a cold start.
If you can get it started it may run all day with fuel a little low. But no start cold.
I learned the hard way.
Also a good acurate gauge is a must to have.

Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT

__________________
Remember proper testing gives us the answer to many problems.
MT

med1212

I clamped of the return line and had a reading of 85 lbs but it bleeds down pretty fast. I got a scanner from Autozone and it reads " P 1870 Manufacturer Contrl transmission" 1 and 2 codes. However it still won't start.
Any other suggestions?

drew300

It starts on starting fluid, but won't start with 85 lbs of fuel pressure.
You've proven you've got ignition.
You've got fuel pressure.
Next guess would be the injector control.
Sorry, I don't have a lot of info on those, other than I've seen "selenode lights" to see if the injectors are getting their electric pulse.
There must be a fuse in the circuit.
That's about it from me

MT-2500

Check for good hot spark to two or more spark plugs.
If you have good spark check for injector pulse.
Did the scanner show any injector pulse or rpm reading?
If you got a node light check for injector pulse.
You have to have spark and fuel pressure and injector pulse for it to start.
Good luck MT

__________________
Remember proper testing gives us the answer to many problems.
MT

med1212

The onlything I can get out of the scanner is the "P 1870 " code. It says it is a "Manufacturer Contrl Transission" whatever that means, any idea?
Also, what is a 'node light" to check the injector pulse? I asked at Kragen and Autozone and all they have is the code scanner.
It is a weird problem, we drove to church on Sunday and it wouldn't start and I had it towed home.
Bummer!

MT-2500

Do you have good hot blue spark to two or more spark plugs?
A node light is like a test light but is for testing injector pulse. It will blink if you have pulse when you hook it to injector wire.
Any good parts place or tool man will have them.
MT

__________________
Remember proper testing gives us the answer to many problems.
MT

med1212

Yes, I am getting great spark and 63 lb pressure at the injector and 85 lb when I pinch off the return line. I will try to find a node light tomorrow and check the injector.

med1212

How do you test the pcm? I still have the scanner but it doesn't give me a clue as to the computer. Any ideas?

MT-2500

The only true test on a PCM is to replace it with a known good one!!!!!
But if you have a scanner check for rpm signal when cranking and see if it has injector pulse reading in the pcm. And recheck for codes. And recheck for codes.
MT

__________________
Remember proper testing gives us the answer to many problems.
MT

MT-2500

Also watch your other inputs and outputs sensor readings for normal readings.
If you have a book with the scanner it will help you out on normal reading on all sensors
MT

__________________
Remember proper testing gives us the answer to many problems.
MT

med1212

I must have gotten the "buget" scanner 'cause there are no code explanations in the manual, just very basic operating instructions. Any idea what P1870 pertains to?

MT-2500

I think Blazer forum has code list posted
Also
http://www.troublecodes.net/OBD2/

__________________
Remember proper testing gives us the answer to many problems.
MT