CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Fuel Injector Failure

'89 Caddy with 4.5 V8 multi-port injection. 125K miles. Number 5 cylinder is stone dead most of the time. Ignition checks out fine. Now and then, #5 kicks in and the engine runs fine. No other issues. ECM input to injector is good. No ECM trouble codes or CEL. (!)



Is this a possible injector failure mode, where they simply cut off, then work for a few minutes before failing again?? Caddy forum agree it’s a failed injector which they claim is quite common…They recommend replacing them all, since the fuel rails must be removed with the injectors to service one or all…

Replacing them all can get really expensive.

But before condemning the injector, make sure it isn’t an injector connector issue where there’s a poor connection. The early GM fuel injected engines had problems with these connectors where you could purchase aftermarket connector kits that you could splice in. I replaced a few in my day.

Tester

I would disconnect the electrical connector to the fuel injector, and reconnect it. The wiping action, which occurs during the disconnect/reconnect, could make a better contact in the connectors.
An alternative to a blind fuel injector replacement is to swap #5 with another. If the misfire changes position…

The connector is high quality and I’ve had it apart and cleaned and “tightened” it. No improvement. I can buy a complete set of new injectors on e-bay for $139…These are claimed to be OEM parts which are being cleaned out of inventory as obsolete…Some have suggested trying to listening to them with a length of hose or tubing. They say you should be able to hear them click on and off…I haven’t tried that yet…

This car has a cool feature where you can, from the drivers seat, manipulate the heater control buttons and turn off the injectors one at a time and observe the rpm drop…There are about 100 other diagnostic tests you can do that way, but it’s easy to get led down the yellow brick road and into the twilight zone…

Caddyman - Do you have a noid light you can use to check the connector is getting power and a grounding signal from the ECU ? If you don’t have a noid you can use a multimeter.

With the ignition on, 1 terminal should be getting voltage, and the other terminal should not. If you back probe the non power side of the injector with the other meter lead connected to the battery positive and crank the engine you should see the ground signal being sent by the ECU. A test light is actually better for this test.

If the power or ground signal aren’t present, check the wiring all the way back to the ECU, clean any connectors with electrical switch cleaner and coat with a little dielectric grease.

Last but not least, check the injector resistance across the terminals, I’m not sure what your Caddy injector resistance should be so just check another working injector first to get a reference. Also check each terminal to ground resistance, if continuity is detected then the injector is dud.

Thanks Scudder, that was helpful. The ECU checks out, the injector is dead…