At wits end with 86 Carrera troubleshooting
 

My ’86 Carrera has not been running well at all. Mileage is 151,xxx. It failed emissions testing last week with the following results:

Idle HC – 913ppm. High idle HC – 511ppm (max is – 220ppm), CO% was 0.03 for both tests.

The car will barely idle, and has a misfire throughout most of the band. This is the obvious source of the high HC numbers, but not the only symptom. Low-load, steady state operation within a varying 200 rpm band (but always between 2k and 3k rpm) results in stuttering and bucking until throttle position is changed slightly. Idle does drop when the oil tank cap is removed.

So far, I have replaced; distributor cap and rotor, spark plugs, plug wires (new Magnacores), speed and reference senders, and multiple vacuum hoses.

I’ve also shifted AFM pickup to un-worn track, checked DME relay against new one, performed valve adjustment, tightened intake manifold bolts, checked operation of full-throttle and idle microswitches, checked temperature sensors for CHT (updated sensor in 2009) and AFM, run the car with idle microswitch disconnected, run car with O2 sensor disconnected, and cleaned and checked operation of ICV on the bench.

Next, I plan to isolate any remaining vacuum leaks, check fuel pressure, electrical ground connections and perform testing on ICV, CHT, and speed and reference senders while the engine is running.

I have searched the forum extensively, yet I am clearly missing something. Symptoms have been fairly consistent for over a year. Your help is appreciated.

While you have run w/o the O2 sensor, have you considered replacing it?

It's on the list, but further down... Should I move it up?

My 3.6 exhibited those symptoms a few years back....ended up being the bad signals from the 02 sensor.

Thanks, JB. Up the list it goes.

Sounds like it could be lean misfire. Your fuel pressure may be low (? plugged fuel filter) or fuel injector malfunction (dirty, bad electrical, etc.).

Steve,

Is that based on the low CO%?

Chris

Have you performed a compression test? This may help rule out anything catastrophic.

compression and leakdown tests next. the leakdown may show more than just a compression test. you need to know that you have a good base to work with. at 151K, it should have had a top end job done by now. was it? otherwise, i would suspect worn guides and the resulting very worn valve seats could contribute to your problem.

Minus leak down test that is very wise, have you tweaked the AFM bypass screw at all in the past?

No top end work, yet.

I asked for leakdown during PPI. Shop said that it would be pointless, as compression test was fantastic (~180#, IIRC) across all cylinders. BUT, that was at 87K miles... Was told at the time that not all 3.2s would exhibit the guide wear issue, and that if I might be one of the lucky ones.

Neither leakdown, nor compression have been checked since then.

I have never touched the afm bypass screw.

The confusing thing, is that the misfire is not steady on one or two cylinders. If I pull plug wires one at a time, there is always a slight degradation in idle. Plug inspection doesn't reveal any smoking guns, either. Shouldn't I have steady indication of a faulted cylinder?

BTW, thank you for the help. I'm tired of tearing my hair out.

Chris

That is a very low CO and certainly suggestive of lean condition (0.1% roughly correlates with an AFR of 14.7) but I don't know how your catalytic converter is affecting the level. Lean misfire is very easy to induce in these cars. I have a difficult time getting mine to idle well at anything more than an AFR of 14 (about 1% CO). I didn't see coil replacement on your list above.

Coil is about 4 years old - which means nothing. Will add that to my list of checks.

Thanks

bosch silver coils are bad juju. very high failure rate.

Notice any change in your brakes? The brake booster takes the largest amount of vacuum. If the diaphragm has a leak, it could result in a large vacuum leak and lean misfire.

+1 on the 02 sensor. your car is exhibiting the exact same symptoms my 84 carrera did prior to changing out the 02 sensor; my car ran perfectly after the sensor switch.

ymmv of course.

Do they often fail partially, so that the car will still run, albeit poorly, or do they just plain stop working?

The original coil that was on my car for 15 years failed, and the car would miss and ran horrible. A new coil was a instant cure.

John, do you know of a source for a top quality drop in replacement coil?

How about checking the fuel filter and injectors?

check for intake leak - easy to do and IMO a good candidate for this high HC readings

O2 sensor should not effect the HIGH HC #'s

basic tune up items (cap, rotor, plugs, wires, coil) would be good to know condition of

oops...CO% 0.03??

that is too low and may be your issue...lean miss
raise that to 1.0 pre cat reading

still could be intake leak though - check for it

Sorry for the delay in response - lots of information to absorb, as well.

Plugs, wires, cap, rotor, and fuel filter are 3k to 5k miles old. I will be checking fuel pressure soon...

The coil is, in fact, a Bosch silver coil. John, is there a sure-fire test to determine whether or not the coil is failing?

The 0.03% CO was the tailpipe measurement, so I don't yet know what it would read pre-cat. In fact, I'm not sure how to get this measurement. What is the process?

Brakes do not feel any different. This wouldn't surprise me, as any vacuum leaks have been present for quite some time.

This week I will replace the O2 sensor, check the coil/swap with my old one, perform a compression test and fuel pressure test, plug all vacuum lines not absolutely required to run the engine, and replace the rest of the vacuum hoses sitting in my garage. Sound good?

Thank you again!

How come everyone is so reluctant to swap out fuel injectors? You can get them flow tested for $25 apiece, get rebuilt ones from here for $45, new similar ones from motorman for $45 or used ones for $30.

there is a plug in the front of the cat you remove to get the readings pre-cat

that plug is very easy to break off so make sure you have all your attention on it and be very gentle and liberal with the lube of choice - work it SLOW in ant out - SLOW dont let it get hot

not that this is your problem, its just the place to set CO% if you have a cat

Just performed compression test. Engine was cold and cylinders dry. All cylinders were 160-165#. That's within 3%, so I'm thinking that the platform is sound...

Off to plug vacuum lines.

Chris

Compression sounds good. Verify the gap on the new sensors? Pull the connectors and check for resistance just to make sure. New doesn't guarantee they are good. Did you check the AFM with 9V battery after you moved the wipers? Check the AFM temperature sensor?
Just for fun, pull the spark plugs and see if any look different. Carbon from oil, wet from gas, new looking as if it is not getting fuel. Pull the wire connectors off the injectors, get a meter and check the resistance across each one and see if they are consistent. You could also apply V to each one and see if they click open and closed. I bought a used '86 that sat for awhile. 2 injectors were stuck closed. I managed to free them up by spraying with carb cleaner and tapping them while intermittently applying V. Pull the distributor cap and rotor. Do they look good without rub marks or carbon pitting. Do the distributor weights look clean and lubricated, move freely?
I ran mine for 1000 miles with no O sensor and it ran well. Have you removed the oil cap while idling to see if rpm drops? If not that would indicate a vacuum leak. Check the 2 vacuum lines on the cruise control module by the fuel filter are connected.

Sorry for the delay in reporting the resolution. Time ran short, so I had my shop handle the rest of the troubleshooting...

Smoke testing showed a massive leak on the #3 intake runner. Once the manifolds were re-sealed, the engine ran well. What was interesting, was that no amount of starting fluid sprayed around the area gave any indication of the leak.

Bodymotion (Ocean, NJ) re-sealed the intake manifolds for a grand total of $847, and had the car back to me in a day. YMMV, but I thought this very reasonable, and would recommend that you give them a try if you need something done.

Thank you for all of the great input. I will still be taking your suggestions to improve driveability, as there is still improvement available.

Chris

Yep..3.2s like to suck in the intake gaskets. Probably a good idea to replace them from time to time.

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