Running on 5 Cylinders

[abair]

I have a 1994 SHO 3.0 and it suddenly started running on 5 cylinders; On Friday it ran fine, on Monday it ran on 5 cyls. from the moment I started it. There aren't any unpleasant noises other than the sound of running on 5 cylinders. According to the EEC-IV "cylinder test" (initiated by tapping the gas at the end of the KOER test) cylinder 2 is bad. I have diagnosed that it is not an ignition problem by installing a new plug wire, swapping plugs, and swapping connections on the coil (since it fires a pair of cylinders at a time) because the KOER Cyl. test still indicates cyl. 2 is bad. I checked the cyl. 2 fuel injector by using a screw driver as a stethoscope and could NOT hear clicking like I could on cyl. 1. I removed the intake and checked cyl. 2 injector wires from the PCM and Constant (?) Relay and they have continuity. I measured resistance on both cyl. 2 and cyl. 1 fuel injectors and they are the same. The only things left to do (as far as I can tell) are a compression check and repair as needed, replace cyl. 2 fuel injector, or replace the PCM.

Does anyone have any helpful suggestions before I start taking more things apart and buying expensive components? Thanks!

 

[sdpatt]

It looks like you have logically followed the trail of the malfunction down to the non-operating injector. If there is current at the injector's connector, chances are that the injector has failed. Either reworking or replacing the injector would be the solution.

 

[Mike Kopstain]

You're best bet is gonna be getting a new set of matched injectors from SHOshop. They are flow tested and relatively cheap. Failure on these is rare, but compare the price of one from Ford to the price of a whole set SHO shop and you'll see where I am coming from.

 

[luigisho]

I agree with Mike on injector purchase. You can get 6 used, cleaned, and flow tested injectors for about the same price as 1 new one from sho shop.

 

[pjtoledo]

abair:
I have a 1994 SHO 3.0 and it suddenly started running on 5 cylinders; On Friday it ran fine, on Monday it ran on 5 cyls. from the moment I started it. There aren't any unpleasant noises other than the sound of running on 5 cylinders. According to the EEC-IV "cylinder test" (initiated by tapping the gas at the end of the KOER test) cylinder 2 is bad. I have diagnosed that it is not an ignition problem by installing a new plug wire, swapping plugs, and swapping connections on the coil (since it fires a pair of cylinders at a time) because the KOER Cyl. test still indicates cyl. 2 is bad. I checked the cyl. 2 fuel injector by using a screw driver as a stethoscope and could NOT hear clicking like I could on cyl. 1. I removed the intake and checked cyl. 2 injector wires from the PCM and Constant (?) Relay and they have continuity. I measured resistance on both cyl. 2 and cyl. 1 fuel injectors and they are the same. The only things left to do (as far as I can tell) are a compression check and repair as needed, replace cyl. 2 fuel injector, or replace the PCM.

Does anyone have any helpful suggestions before I start taking more things apart and buying expensive components? Thanks!

Better take another look at the schematics. The way the power goes is:
1. CCRM has a relay that sends power to all injectors at once, it is always on if the engine is running. That power goes through several splices,,be sure to check them.

2. the PCM,,thats the computer, 1 at a time grounds the other side of the injector, that completes the circuit and fires the injector. There are 6 transistors inside the PCM, 1 for each injector doing this.

3. With the key on, and the CCRM and PCM doing their thing, you will see 12v on the red lead,,,that's from the CCRM, and WHAT LOOKS LIKE 12 v on the other lead!!! If you put an O'cilloscope on the other lead you will see short pulses dropping to near zero volts. Most meters average those short pulses, so you cannot see them. I haven't tried it yet, but one of those real cheap test lights that have an LED should show that pulse, but it may be a real fast one and hard to see.

When an injector is firing, there is 12v on the red wire, and near zero on the other one.
A malfunction,,open circuit inside the PCM will keep 12v at both wires on the injector, no pulses.
So, if you see 12 v at the injector, the CCRM is good. If you see 12v on both sides of the injector, it too is good. That leaves the PCM and wiring going to it.

Hope this helps.

Perry Toledo,Ohio

<small>[ April 22, 2002, 10:10 PM: Message edited by: pjtoledo ]</small>

 

[abair]

Thank you all for responding so quickly.

Perry, I really appreciate your detailed recommendations. Currently I have the intake removed to gain access to the fuel injector connectors; I did not seem possible to access the connectors w/o removing the intake. Can I take the measurements you suggested without the engine running? A mechanic friend of mine told be that cars w/ EFI fire each injector at least once when the key is initially turned on. If this is true will this one pulse be sufficient? I witnessed the pulses you described when I measured the voltage across both leads (not from the leads to ground) with the key on only. With the meter on DC it just fluctuated but it settled right on 0.07 volts on the AC setting. I will take the measurements ASAP and hopefully I'll have good luck and news to report. Thanks again.

Adam

 

[jcostantino]

You could always take an injector from say #3 and swap it with #2 and see if the problem moves with the injector.

Jeff

 

[abair]

Here's a small update on the diagnosis of dead cyl. # 2 described above. Following Perry's advice I measured the voltage between the red wire (from the CCRM) and ground with the key on. 12V was indicated. Then I measured the voltage between the other wire (from the PCM) and ground with the key on. Near zero volts was indicated. It's possible that the other wire went to 12V too quickly for my meter to read when the key was turned on. Anyway, the injector DOES work because when the key is first turned on, it sprayed fuel onto my finger. This happened on cyl 1. and cyl. 2. I seem to be dangerously close to blaming the PCM or a compression problem. Does anyone have advice on where to get an M14 "extension" so I can actually tighten the compression test fitting firmly against the head?

 

[abair]

It has been nearly 3 months since the last post on this discussion string but I have great news to report. After eliminating DIS failure by swapping wires and plugs in various ways and checking compression (Both checked out OK) I was left with the choice of replacing the injector on the bad cyclinder or the computer. I chose to replace the computer and the car ran beautifully after running rough for the first few minutes as it sorted things out. It was a bit of a gamble at $222 ($100 core, $322 total purchase price from Ford dealer compared to $90 for a single(!) injector) but corrected the problem. The Service and EVTM Manual from FORD were very helpful but the helpful people on this BB were indispensable. Thanks everyone!

 

[sdpatt]

That was a good ending to a challenging problem. Excellent work.

Scott