Intermittent skip?
 

OK, I'm losing it. 92 fb 305 TBI has had a phantom CEL for two years, never stays on more than a minute or two, usually on the highway. Recently, it developed a noticeable skip. It bucks a little under light load at 30 mph (3rd gear converter lockup), and you can feel it stumbling on the highway a bit. Recently replaced injectors, rotor, cap, coil, and just this morning the ignition module. Put a timing light on any plug wire and I can see the occasional miss. Plugs aren't very old, wires are 10 years old but nothing obvious wrong. What else could it be?
It seems to get worse when it's warm, but that might just be the high idle hiding some of the problem. The car still only has 82,000 miles. Most of the vacuum lines are original, so something could be leaking a bit, but that doesn't seem to match with the timing light skip.

Any ideas? I've got a few other mechanicals to fix (door hinge bushings, ball joints, and a window motor), and I'm getting a price on some floor, wheel well, and body repairs. This has been my daily driver for 10 years after buying it from the original owner, but now I'm also looking for another rust free low mile one to drive if this one is going to cost a lot of time or money to stay reliable (or keep aggravating me with what seems like it should be a simple repair). I can't take the time to tear it down myself--too many other projects.

Thanks!

Re: Intermittent skip?
 

What code is being stored by the ECM, if any? The CEL should have generated something, unless it was flashing instead of remaining on.

Re: Intermittent skip?
 

The first thing I would do is unplug the ECM and then plug it back in again after inspecting all the contacts.

If you have a crusty connection, its gonna do the bucking-bronco thing.

I replaced my ECM (after parts-cannoning damn near everything else to no successful effect). After replacing the ECM, the stuttering and bucking bronco thing was permanently gone. In retrospect, I doubt the ECM itself was the problem. I now suspect it was just the nearly 30-years crusty connection. The action of unplugging it, and re-plugging it to a new ECM probably knocked-off enough crud to restore a reliable connection.

Consider giving the harness-plug and ECM-pinout-jack a good cleaning while you have it unplugged.

It won't hurt to unplug, and re-plug the PROM chip, and clean those connections too while you're at it.

Re: Intermittent skip?
 

Working tech support over the phone at Gateway for four years, you wouldn't believe the hardware issues that were cured by reseating cards and cables, and this was on new PCs less than a year old.

But yeah, pull the codes. A light should store something. an intermittent problem often gets worse until it finally sets a code. BTDT with the knock sensor, fuel pump relay, and VSS failures. None of the above set a code with the earliest symptoms of trouble, but set a code awhile later.

Re: Intermittent skip?
 

Highway CEL on a TBI 3rd gen is usually an EGR issue. Now, this is an educated guess, so do pull the code(s) first.

Second guess would be a silicone poisoned O2 sensor. Again, a code will tell the tale. Or at least point you in the right direction. Can use a scan tool to check the BLM (long term fuel trim), if low it points to the O2 sensor.

If the BLM is high points to an EGR issue or a failing fuel pump. Note that there isn't a failing fuel pump code, so need to take everything into consideration.

RBob.

Re: Intermittent skip?
 

Thanks for the replies. The OBD1 only says 12--which means the test light is working and nothing more. I'll try unplugging the computer and looking for bad connections to clean up. It's never been moved or unplugged so hopefully that's it. It has been damp over there, first for a heater core years ago and more recently a firewall leak below the blower motor. Maybe some pins are corroded.

Re: Intermittent skip?
 

You said 92 305 TBI. I am going to assume yours has the same ignition as my 95 305 TBI truck. Two easy things to check: 1) cheap rotors can arc out to the center mounting post in the distributor. You already replaced yours, so that's probably not it. If it were an issue, you have to look for a hair-fine arc line with an eye loupe. The spark goes from the coil to the coil connection on the distributor cap, but nothing comes out to the plugs when it completely fails. It is intermittent before that.
2) The pink and white wire coil jumper harness is a known failure point. Remove it and check for corrosion and test it with an ohmmeter.

Re: Intermittent skip?
 

I know you said you replaced the coil but I would do a quick primary and secondary resistance check, just because it's new doesn't mean it's good. Coils tend to crap out when they get warm. Also check any ground wires related to the ignition. I like using this stuff on all the wire connectors.http://www.acehardware.com/product/i...nt=Catch%20All

Re: Intermittent skip?
 

Technically, that is not completely correct. 12 means missing distributor reference pulse. That always occurs when the engine is not running, so some people erroneously interpret that as "normal" when it can actually be a DTC set while running.

Poor performance of the pickup coil, corrosion on the reluctor poles, poor connections of the pickup coil or HEI module, or anywhere in the primary ignition system can cause that.

Re: Intermittent skip?
 

Re: Intermittent skip?
 

...So I may completely disable the car when I disconnect the ECM to check the terminals?! How insecure are the plugs without the clips? (If they self-destruct is tape a temporary option?)

Now I'm glad it turned cold & rainy yesterday so I didn't already try this.
I don't have a spare car to take to work, so waiting for new clips from Hawks if they break really isn't a good option.

Thanks

Re: Intermittent skip?
 

I'm pretty sure you can just throw away the gray and blue clips, and still get connection.

The black plugs fit pretty tight. Problem is, they engage the ECU from the bottom. Hot/Cold cycles plus vibration, I'm sure the black plugs will work their way loose without the gray and blue clips.

There are ways to improvise with zip-ties or some such if you wer really in a pinch with loose ECU/harness connectors. But, in the grand scheme of things, I think we should be grateful that Hawks has the unique part we need, even if Hawks is demanding to make a profit on the sale. I'm OK with that.

I'm sort of a zealot at this point. I have (at least one) spare ECU, and I'm working on getting up to speed on copying the EPROM chips, and re-wiring the circuit board in the ECU. The tools and parts aren't free. But they really aren't that expensive by comparison. What would you rather have? A whole new set of soldering tools, or one night at the Sheraton by the ocean somewhere? Its a no-brainer for me.

The only thing I find expensive about playing with these cars is my TIME. Like it or not, time is absolutely irreplaceable. So long as I'm having fun, the time goes by without pain.

Re: Intermittent skip?
 

Glad there's a way to rig it, if needed.
Time and money are always the killers. I can't work full time, maintain/update our house, manage everything else we do, and spend too much time fixing my daily driver. I've also had plans for 2 years to switch it to 5-speed, but I'm not wasting the time until I'm sure everything else is solid and working properly.

The car project that is expected to take my time is building my 71 Camaro for our son to drive.

Re: Intermittent skip?
 

The clips have prongs that hold the pins fwd. the pins have locking tabs so they have to be pushed down to release them from the connector.
If you need a ecm you can look on eBay or check the classifieds here and swap over your prom. The ecm is a service number 1228746 and was used in 89/92 tbi .

Re: Intermittent skip?
 

I wrote a (somewhat long) piece about the "clips" that hold the wiring harnes in place with the ECU.

https://www.thirdgen.org/forums/tech...-computer.html

Re: Intermittent skip?
 

So I unplugged the computer, checked all the pins and plugged it back in.
The good news--the blue and gray clips were fine and the pins all look great. No signs of corrosion or any other issues.
The bad news--the car still runs every bit as bad as it did.

My multimeter broke, but resistance checks and grounds are next.

Any chance something else in the distributor could screw this up? When I was replacing the rotor and module I noticed that I can rotate it several degrees and it stays there. IT moves kind of stiff and there is some rust on the center shaft. I presume it works different when running and the computer corrects for position like an old vac advance would have in earlier models, but should it be stiff to move by hand?

What about the little cap on the shaft underneath the rotor? I think it is just there to keep the wires from the module away from the moving shaft, but it feels loose and rotates maybe 10-15 degrees, too. I'm grasping at straws. I know the older non-computer stuff (and points) much better. They never had anything loose, and always had springs to return to starting position or your timing would be way off.

Re: Intermittent skip?
 

I don't have my CCC distributor in front of me at this moment (yes, I know you have TBI), and someone will correct me if I'm wrong, but computer controlled distributors should have NO ROTATION as you describe. The timing advance is done electronicly. You need to pull that distributor and check that the pin holding the gear on is not broken, that the gear still has teeth, and is the shaft really gummed up, or something else. It sounds like your distributor has seen better days.

Re: Intermittent skip?
 

As NE84TA noted, the spark-advance is controlled by the computer.

There is a brownish wire that usually is exposed from the larger clump of wires that run along the top edge of the firewall. There should be a plastic clip mid-length along that wire. That clip is to facilitate disconnecting the Electronic Spark Timing (EST) when setting "base timing" with a timing light.

When that plastic clip is unplugged, the computer is prevented from doing anything with the timing. Your base timing on a V8 is usually around 8 degrees BTDC. If you loosen the distributor bolt, you can play with the base timing, and listen to the motor change. Assuming the motor is in generally decent running condition, you can usually achieve good base timing just by ear.

If the timing chain/gears are badly worn, and you try to put a timing light on the balancer during idle, and with the EST wire unplugged, you may notice the timing mark on the balancer running around like a rat on crack. It doesn't help either if the elastomer material that joins the inner hub of the balancer to the outer pulley of the balancer has given up the ghost, allowing the outer pulley to not keep up with the inner hub in good synchrony. Then you get a timing mark that runs around like a rat on crack, and bath salts.

As always, check the fundamentals.
Spark quality
Compression quality
Fuel pressure quality
Vacuum leak elimination

You can check to see how much slop you have in the mechanical parts your timing assembly by removing the distributor cap, and observing the distributor shaft while a helper rotates the crankshaft with a socket/breaker-bar. The helper rotates the crankshaft until the distributor begins to rotate. Then, have the helper rotate the crankshaft in the opposite direction until the distributor shaft rotates in the opposite direction.

In a perfect world there is little-to-no slop at the distributor when the crankshaft is rotated. The more slop there is, the harder it will be to achieve good driveability.

Re: Intermittent skip?
 

Well, unless it dies this is likely to become someone else' problem. I don't have time for the rust repair (rear wheel wells are the worst issue, but rockers, and a couple spots in the floors have holes, too) that the car now needs to pass inspection in June, so I'm not wasting time or money fixing this. :mad:
It'd be a great car for someone with the time to fab and weld the spots.

I'm looking for another 3rd gen to drive. I'll keep driving it while I look, but I'm hoping to find something quick.