Fuel injector testing

[greekguy7]

My '88 Grand Prix 2.8litre hesitates and stumbles badly under load, and cranks but wont restart when its hot. When it wont restart, I tested for spark and fuel pressure is 42psi when cranking. I was thinking its the injectors, so I pulled the plenum on the car and measured them.

On the front bank, they read:

11.1 ohms

9.5

9.5

and on the firewall side, they read:

12.2

12.3

12.1

I was hoping I find one or two injectors reading more like 3 ohms making the decision easier. Do you think the front 3 injectors are out of spec enough to cause severe hesitation and starting problems?? Thanks!

[Slade901]

When you say it will not start when it is hot. Does the engine even turn over or not at all?

 

I would assume that the engine turns over when the engine is still hot when you try to crank it.

 

Check your vacuum hose from the fuel pressure regulator when you try to start it to make sure there is no fuel coming out of that vacuum hose attached to the fuel pressure regulator. If there is a fuel on the vacuum hose attached to the fuel pressure regulator then you may have to replace the fuel pressure regulator.

 

Does this happen also when the tank is full? In-tank fuel pump uses the fuel around it to help operate cooler but once the fuel is way down then it tends to operate hotter and probably starts to fail and it starts to probably suck in dirt when it's low on fuel, etc.

 

Not sure about the specs on your fuel injectors. Someone might know the tolerance of the fuel injector readings.

[greekguy7]

Once the car is hot, it will crank but wont restart. Tank is full of gas.

 

I checked the fuel pressure regulator and its not leaking any fuel out of the vacuum hose and pressure holds steady when the car is off. Fuel pressire is 42 while cranking but not starting, 37 when the car is actually running and around 40 or so when the key is turned to ON. so i would think the fuel pressure regualtor and fuel pump are fine.

[Slade901]

A couple of things to check for.

 

While it is hot and not starting. Check for sparks at all spark plug wires. You can use those clip-on type spark tester and see if you all sparks.

 

The location of your ignition coil and ignition coil module is probably near the engine block subjected to high temperatures and probably have to get it cool down a bit to get it fire up again. Possible ignition coil or ignition control module maybe getting bad or it's heat-sink behind it is loose and not able to transfer the heat back to the engine block.

 

You could have excess fuel in the cylinders and have to wait till they dry up to get it to start again. Try putting the gas pedal all the way down for a few minutes before try to start it again.

 

Are you loosing power when driving? It could be the catalytic converter is partially clogged up and have to wait to cool the engine down before starting again.

 

The EGR might be bad and stuck open all the time and letting the very hot excess exhaust gas to come again into the intake. Some folks try to block the egr completely since its purpose to help the environment and reintroduce the exhaust gas back into the engine to get it burn the again.

 

Check the crankshaft position sensor wires and make sure it is not rubbing to the engine block. Also, make sure that the crank shaft position sensor is still good and not failing. No signal from the crank shaft position sensor, you will not get a spark from the ignition coils.

[greekguy7]

What do you think of the readings I got above for the injectors? You think they are out of spec enough to cause a problem?

[Canada]

I would definately replace the 9 ohm injectors.....11 ohm is your call. Low resistance isn't the direct cause of a no crank when hot, but it maybe those injectors that are leaking down fuel....or it might be all of them.

[ns87]

I only had 2 that were out of spec, so thats all we replaced. The new ones worked so much better than the "OK" ones that it caused the same problem again and burnt out my fuel pump. I consequently replaced the pump and the last four injectors. Just save yourself some hassel and replace all injectors at the same time.