chris1

I just purchased my 1986 Convertible 4+3 earlier this month, and am trying to get a bunch of stuff straightened out; the car never really had any power over 2,000 RPM's since I got it, so I was hoping that after my tune-up, it would be corrected, however it seems to be a little worse now; the check engine light will come on occasionally and I was able to pull codes 42 (Electronic Spark Timing (EST) & 44 (Lean Exhaust Condition); here is what I've replaced so far (all AC Delco parts)

Plugs
Wires
Distributor Cap
Rotor
Ignition Module
Oxygen Sensor
Coolant Temperature Sensor
Fuel & Air Filters
Even the sock filter attached to the in-tank fuel pump
Ignition timing set at 6 degrees
TPS set to .54 volts
Lightly tapped on the MAF sensor with no RPM change

I'm pretty decent with these L98's, however this has got me baffled; the car will sit there an idle perfectly, no missing or shaking; you can even rev it up and it sounds strong, however as soon as you get it over 2,000 rpm's when driving, it has no power and starts bucking and hesitating; it almost seems like the cats/exhaust is blocked; not sure if it could be fuel or ignition related; I did the diagnosis for code 42, and it led me to a possible bad ECM? Was going to try and replace the ECM and ESC Module to eliminate those 2 items; any additional suggestions before I take it to my mechanic? I went back over and double checked all my work, and everything looked fine, and as I said before, it still is showing the same symptoms (maybe even a little worse) than before I started my work; it's keeping me up an night trying to figure it out; wish I knew so I don't have to just throw parts at it...........

Thanks for any help or suggestions, Chris

leesvet

Any reason to believe that its NOT plugged CATS? Thats happens everyday. I've had it happen.

To test, pull the o2 sensor and start the engine. If you can feel exhaust blowing out the o2 hole..the cats are plugged. The max back pressure is only 3 psi..MAX.

whats the fuel pressure? you need 40 at key ON..no cranking.

38-45 psi steady at idle.
Buy a FSM set and STOP throwing parts. The books are only $75 used and will save you ...several Hundred RIGHT NOW.

If your ECM is bad then it will likely NOT give the proper response when you read the flash codes. Try that and look for the all important 12. Before and after.

hemivett

I had an o2 sensor do that to me before. Started, and idled fine, but anything above 1/2 throttle. it would just nose over. h

Cliff Harris

Error code 42 is caused by disconnecting the EST connector to set the timing (among other things, but this is guaranteed to set it). Try resetting the ECM by disonnecting this connector for a second or so:



Error code 44 is an O2 sensor problem. It could be fixed by the ECM reset. If it's still there after the reset then look at the wiring and connector first and replace the sensor if the wiring looks OK.

Bad running above 2000 RPM could be a bad/poorly connected plug wire. You might have two plug wires crossed. It's amazing how well an L98 will run on only 6 cylinders...

chris1

Thanks; I have the factory service manual and made sure I labeled everything before I replaced the plugs and wires; my distributor still had the wire hold down with the cylinder numbers on it that most cars are missing, so it was easy to use that as a guide as well; pretty sure the cats are plugged; got them on order, so hopefully I'll be all set after this weekend; will post my results.....

chris1

Lee: Thanks for the info; I do have a FSM; I always give my cars a complete tuneup when I purchase them, so I haven't really thrown any parts at it yet other that tune up stuff; fuel pressure is 44 with key on, no cranking; pressure is at 36 psi when idling, and 46 after I disconnect the fuel pressure regulator, so I think I'm OK with the fuel; FYI; the pressure will drop pretty quickly from 44 with the key on no cranking, so hopefully that is not a problem; I feel pretty confident that it's the pre-cats and main converter that are plugged up pretty good; it idles perfectly smooth, just stuggles for power like something is plugged when trying to accelerate past 2,000 RPM's.....

chris1

Thanks for everyone who responded; I replaced the front y-pipe with the pre-cats and the main catalytic converter, and all is well now; what a difference now that full power is pack; I guess after more than 25 years, it's a wonder that they weren't even worse; it just passed inspection with flying colors; thanks again for the help and suggestions....

leesvet

Have you ever seen a tree with a cable inside that the tree grew around after 50 yrs?

Thats what clogged cats is like...it happens sooooooo slowly that you just do not know whats going on until it won;t run.
last time it happened to me, the car would not get past 60... within 30 miles it would not get over 30.... I limped into a non-hostile muffler shop in Santa Ana Ca and they "removed" the problem...with a beater bar and a hammer.

On my current motor when I built the exhaust system I took all the cats and mufflers out. I'll never forget the feel when I first fired it up...it revved from a 600 rpm idle to 6000 between heartbeats ! NEVER, EVER did it rev that fast before because of the cats.

Glad you got it sorted out. I figured it was dead cats. When fuel is ok, it comes down to cats. The only 2 systems that cannot set a specific code.

chris1

Lee: Yup, it feels like a different car; kinda like the shocks, they degrade slowly over time, so it hard to tell, then when you finally replace them, it's such a big difference; thanks again; now to diagnose and correct the cruise control and ABS light that is on.....