'96 PCM TBI running rich

[96 LaBrisa]

I've got a '96 La Brisa with a PCM 351 TBI-equipped engine. Engine is idling really rich after it gets up to operating temps. Here's the data I hope is needed:

Fuel pressure at the TBI: 15 psi
Plugs and wires are good, plugs come out sooty on all eight cylinders, no oil on the plugs
Coolant temp (at the gauge): 170-180

Ok, now for the symptoms. Engine starts fine cold, but once it starts warming up a rich gassy smell starts being noticable. As the engine comes up to temp this gets worse, with black smoke at idle and skiiers passing out from the fumes (slightly exaggerated, but you get the idea).

Once the engine is up to temp, engine starts get harder, sometimes requiring throttle movement with the idle pin pulled to get things going. Once running the engine will idle OK, but still very rich. Coming out of the hole the mid-range will stumble, but once above 1500 rpm or so things clean up and she runs normally.

I get a slight amount of blue smoke on startup, which I attribute to oil leaking past the valve guides. However, this is just a puff, then back to black nastiness.

I have found absolutely no one that knows anything about TBI systems locally, and neither Holley nor PCM have been any help, either. No one has any diagnostic equipment for the computer, so I'm going to try to figure out if I've got a sensor problem, or maybe add an adjustable fuel pressure regulator (which I hate to do since the engine runs fine at speed).

Unless it's a computer problem, I'm leaning towards the following:

1. Engine temp sensor (to the computer) stuck at cold
2. MAP sensor reading too high
3. A vacuum leak around the MAP (where would vacuum leaks reside, anyway?)

So, how the heck do I check these sensors? I've done an "it's alive" test on the temp sensor, but how can I tell if it's right or not?

TIA for any help y'all can give, and have a good one,
Mike

[96 LaBrisa]

While on vacation last week I finally found the problem of my engine running rich. I don't get to go out on a frequent basis, and this was the first time in a year that the boat was run on a daily basis.

Engine started the week running pretty well, but got richer and richer, gassy smell, black smoke, gag!!!

I'd been inspecting the engine compartment daily, and would smell fumes, but it wasn't until the 3rd day that I finally had enough and started tearing things apart.

First, I did a real close inspection around the throttle body, and found where fuel had actually been leaking OUTSIDE the throttle body assembly, running down onto the intake manifold and puddling! EEEK!!!! Then *real* close inspection showed the fuel was leaking out of the injector assembly where it mates to the lower portion of the throttle body.

When we took the injector assembly off the top of the throttle body, we found that the o-rings (4 in total) that seal the fuel feed and return circuits (where the injector and throttle body assemblies mate) had hardened and turned brittle. 4 new 25 cent o-rings and I've got a new engine!

No more blue smoke, throttle response like when we bought the boat 10 years ago, life is good!

Hope this helps someone else out.

Have a good one,
Mike

[Brian Raymond]

Mike, thank you for the info. Great job on the diagnostics and repair. Brian Raymond