[turk]

The story continues with my Caddy but I figured a new thread was appropriate. Put the MCS screw in the carb back to 1 1/4 turn, just like I found it. Measured the IAB per the service manual gauge spec, and set it as close as i could without the unobtainable gauge from GM/Thexton... Fixed bad plug wire, drove it yesterday and it ran great, except for a code 34.... My 44 is now gone and no drivability issues, idle was good, with a very slight hiccup every once in a while, hardly noticable.

I replaced the air shocks yesterday afternoon and figured I'd work on the code later, since it was running well. This morning heading to work, it starts, and runs great until about 5 milles from my house, at which point I am getting hesitation/lack of power and what sounds like backfires. loud pops and a hesitation. I'm on an expressway at 55 to 65 mph at this point.... No power on an incline, but if I really put my foot in it, it will accelerate somewhat. Then, the pop/hesitation again...

This one has me stumped, as it has never backfired/popped before... I can't find any vac leaks, the hoses look good, everything is hooked up.....

Any thoughts, folks? map sensor maybe? (the manual calls for a scan tool to check the voltage for that, which i do not have...) I'll triple check that the plug wires are in proper sequence but i am sure they are..

 

[outsider]

Code 34 is 34: Shorted MAP sensor circuit fault per the tech thread.

If you have a manual you could try to find out how to diagnose a short in it, but as you said it might require a scanner of some kind.

Do you have the olds 307 engine? if so, I could try to look at my 87 brougham manual when I go home.

 

[turk]

I got home from work and opened my mail. I had a set of carb tools, circa 1985, I just bought on ebay for 20.00. I gauged the IAB valve, (it was off) and checked again for loose vacuum lines. Sure enough, the MAP sensor air line was loose, but the connection was inside a piece of regular sized vac line and you could not see the disconnect. Lesson learned...

I drove it 20 miles, no codes! We are making progress.

The bog/pop/hesitation is still happening. I notice it when gradually increasing throttle, especially on an uphill...

If I floor it, it howls, then kicks in and accelerates. It's a little like turbo lag, for any diesel owners out there. But only when I floor it, any more gradual throttle, and the hesitation/pop occurs.

Outsider, thanks for the offer. I do have the 89 service manual, and it is a 307 Olds...

It idles well, although it's got a bit of high idle when warm and in park. With engine load on the motor the idle is very nice...

Is this not enough fuel from the secondaries? What if I shim the secondary cam a bit? Any other thoughts?

 

[sven914]

Have you done anything with your AIR pump?

The Air Injection Reaction (AIR) system used two computer controlled switching valves. One is mounted to the back of the AIR pump and the other is next to the passenger side valve cover. If the ECM commanded valves are not functioning properly, they can cause either an exhaust or an intake backfire. Other things that can cause backfires are rich running conditions, a defective catalytic converter, or improper ignition timing.

As for the delay in opening the secondaries; I find that to be normal. Mine takes a few seconds for it do anything when I hit the throttle, but I can hear the engine wined up like it's building up to something, then suddenly it takes off like it grew a pair, which only lasts until it gets to the next hill, where I have go back to Cadillacing.

 

[turk]

I have done nothing to the AIR system. It spits out a lot of air when the air filter is off the carb.. Sven, if those AIR valves are misbehaving, will the ECM generate a code?

Latest note on the drive to work this morning. I seemed to have a lot less popping, but on a couple of sharp inclines, I was stuck at 40-45 mph on the expressway with my foot in it all the way. Once I started on the downhill side, it sped back up....

It's really starting to act like a secondary issue of some sort, but I'm still not sure. At least no codes since i got the 34 figured out..

It's strange, since the symptoms seem to change gradually over the last couple of days... It's gone from popping/backfiring to bogging/cut-out or no acceleration at WOT.....

I guess I'll take the carb off one more time, re-do the internals and gauge the MCS and IAB and see if that helps. The secondary air flaps seem to be loose and working fine, no binding or sticking...

Could it be the secondary rods not allowing enough fuel? Would that cause a bog/hesitation?

 

[Garys]

The lack of power on hills and popping / bogging sounds like an issue I had with my '79 FWB. I kept looking at the carb and also for vacuum leaks. It turned out that the catalytic converter had disintegrated and the debris had blown into the muffler, blocking the majority of exhaust. My Cads symptoms would change too as the debris would reposition itself in the muffler. Sometimes it would run great and then sometimes not. Also, check the engine vacuum at idle with a guage. If its low, and you don't have a vacuum leak somewhere, the cause could be an obstructed exhaust. Just a thought.

 

[sven914]

I have done nothing to the AIR system. It spits out a lot of air when the air filter is off the carb.. Sven, if those AIR valves are misbehaving, will the ECM generate a code?

No. There isn't a code for that. It might cause a code 44 (lean O2), but not always.

 

[turk]

I never would have thought of exhaust... I'll check it out and see. Drove the car tonight and pop/bog was worse than on the ride home from work today.

It did pass inspection today including a tailpipe emissions test...

 

[turk]

Latest report. Took the carb apart last night. Gauged the TPS with an old gauge from ebay (1.301 on my caliper, spec is 1.303). I could not get the TPS low enough in the bowl to get the plunger to rest on the gauge and touch the solenoid screw stop on top of the solenoid, and tighten the screw down to make it all stay. The screw will not go down far enough to hold it. I left it half a turn from bottom, but even with the screw all the way down, there was still excess room between the screw stop and the plunger.

Gauged the IABV to spec with the other gauge from ebay, and it synced up fine. I put the old nitrile float back in instead of the new brass one I had in there, and it's dead on at 11/32.. They had significantly different shapes, but were about the same size. Air valve spring at one half turn, per spec.

I did see black soot in the venturis when I took it apart, so does that confirm backfire in the carb? Or just lean or rich?

Put the carb back together, on the car, drove it last night, one hesitation/pop near the end of the drive. Big improvement.

Today on the way to work, one hesitation and a couple of pops, but otherwise fine, including up a steep on-ramp where it was bogging terribly yesterday...

Not perfect, still a couple of pops/hesitation, but much better. Any ideas on how to get this to not pop/hesitate at all?