eljaro

I have gone through much testing and replacing parts but still donīt get the engine running right.
I explain. I takes quite a while to start, running down the battery on several occasions. Once it starts it idles well for about 2 minutes and then dies. Very hard to get restarted again. Maybe only the next day.
On another occasion I got the engine started I idled it a for a minute and then had it running at 2000-2500rpm one more minute running like that before the engine just died.
There is spark, there is fuel pressure (about35psi) but engine wont start.
The distributor is new (it was badly rusted inside), the oxygen sensor has been replaced, the fuel filter is new and the ECM has been replaced too.
No way to get this engine to start normally nor to keep it running longer than several minutes if it starts.
No error codes out of the ECM. Coil checks out ok, all injector measure 17 ohm when warm.
What is it that will allow the engine to start (albeit with difficulty) and run a while and then die?

defaced

iTrader: (6)

The next thing I would be checking is the MAF, if you have one. When it does start and is idling, does it run rough?

bungy74

mine did that and it was the fuel pump. Is your psi hold at 35 or does it spike there and then drop off? will it start with a shot of ether ?

eljaro

when the engine starts it idles perfectly smooth for about two minutes, then it starts missing and eventually dies.
Remember that the ECM does not show any error code.
I have checked for spark when cranking and it is good.
When cranking is seems like it sometimes wants to start, running for two or three revolutions but does not continue.

defaced

iTrader: (6)

When I put my new 350 in my Bird, I had a bad MAF. Pretty much did the same thing as yours is doing. Could barely start it and when it would start, it would do same as yours. Took me forever to figure out it was the MAF because there were no codes. I found out by unplugging it on accident and started the car shortly after and it started and ran perfect. Saw that the MAF wasn't plugged in so I connected it again, went to start it, and back to the normal problems.

Assuming you do have a MAF, try unplugging yours and start the car and see if it changes anything. You'll at least be able to eliminate it if it doesn't change anything.

bungy74

you should monitor the fuel pressure for the 2 minutes that it idles and then dies, you may see it drop before it dies.

bungy74

also, when it does start, can you rev the engine or will it start sputtering ?

bungy74

another quick test is to boost your fuel pressure by clamping the return line with a pair of vise grips and see if it starts. If it does start then you know you have too low of a pressure

eljaro

I have checked the fuel pressure again and again, and it goes up to 35psi and stays there. There is fuel, because I have sprayed ether into the intake and will not start.
I have disconnected the MAF and still no start.
I have checked the spark coming out of the coil, and it is very strong.
If I look at the spark on cyl.#1 I see a strong fist spark but then the spark gets very weak and I think it just is not there.
Can it be that there is spark going to the distributor but not getting to the plugs?
When I was adjusting the advance and tried to turn the distributor I got several times discharges, which has not ever happened to me on other cars.
I suspect that the plug wires or the rubber (not silicone) caps are bad and the spark is finding its way to mass somewhere.
Could it be bad spark plug cables hindering a normal start?
The car had apparently been for 18 months outside in english weather, damp and wet.
Distributor had rust inside and was beyond repair.
I will try to get some good spark plug wires tomorrow and see what happens.

dhirocz

iTrader: (2)

Most driveability problems with TPI cars are easy to diagnose if you look it methodically and troubleshoot while the problem is occurring. When it stalls, check:

Fuel pressure. Should be at least 40 psi. Should hold pressure after the fuel pump prime. Slow drop off is acceptable.
Injector pulse while cranking. Use a noid light and make sure the ECM is sending a signal to fire the injectors.
Spark. Make sure you are getting fire to the plugs and they arent worn or have an excessive gap/damaged. Easy to check with a spark tester.
Use a scan tool and make sure you are getting an RPM reading while cranking.
check for obvious issues like low fuel, plugged filter, etc

Yes, a bad cap can cause a no spark after a couple minutes of running. Seen it once on a vortec 350. Engine warmed up, cap was cracked, lost spark from the coil terminal with thermal expansion.

Not so common...make sure you have the RIGHT PROM INSTALLED. Ive seen some issues like this, with say an 88 prom in an 89. Prom commands cold start fuel through the cold start injector that isnt there (1989) instead of the primary injectors. This causes a very hard cold start unless you use starting fluid. If there are other issues, it can make driveability issues worse than normal. Just something to check.

Id be willing to bet its a bad pickup coil in the distributor. Just fixed this on mine. Same issues. Check into that fuel pressure. Dont go with a parts store pump, delco or better. Easy way to check...scan it while cranking and check for an RPM reading while it wont start. No spark is also a sign of this. You can also test this with a volt meter and resistance check it hot to be sure though this isnt the most comfy way to check. Its a good way to guarantee the parts are the problem though.

88camaroscv6

iTrader: (1)

that sounds a lot like you have bad fuel injectors, whip out the volt meter and test the ohms out, they should be in the 14 to 17 ohm range, if they are at 10 ohms or anywhere out of that range you have a bad injector, i had the same problem as you, would only start the next day and after that endless cranking

bungy74

you said it will not start on starting fluid , so yes, that means no spark, or no compression. You said #1 spark is there buy not strong. I would take the coil wire off the distributor and put it on a spark plug and check for spark right at your coil, see how it looks there. If it looks good, then you have cap /rotor or timing problem.

eljaro

Today I checked all 8 injectors. I connected them to 12 Volt DC , even going through an amp meter in line, and all of the clicked nicely and drew 485mA.
So the injectors are ok.
I put a plug on the lead going from the coil to the dissy and got a good spark.
But when removing one of the plug caps and inserting a plug in it and holding the plug body against ground I only got maybe one strong spark and then a few weak ones and then nothing.
I removed the distributor cap and the finger and was amazed at the huge gap there is between the finger and the 8 contacts on the cap, in the range of 5mm.
This gap has to be overcome by the spark, and now I am thinking that the coil must be bad. It all measures ok with a DVOM but the spark must be leaking to ground.
I will get a new coil tomorrow and see if I get finally this problem fixed.

eljaro

Got the new coil and the engine now starts and runs well.
The old coil did measure ok, but apparently when it got warm it leaked to ground and didnīt supply spark to the engine. Using a spark plug right out of the coil to check the spark showed a good spark, but when the spark has to overcome the gap inside the distributor it finds an easier way to ground through defective internal isolation. So no spark to the cylinders. Donīt know how the engine sometimes managed to start.

Well, anyway, problem solved.