Hello, Just really enjoying this site ... THX Barth! I don’t own a Barth but they are fine & rare rigs! I came here because of the below issue ... I am finally home now and am at the point of checking timing and that is how I got here ... please read below and if you have any thoughts I'd love to hear 'em ...

I have a 1987 Itasca 22' RV with the 454 (two smog pumps, 70k miles). I had a major power loss while driving on cruise control at about 55 mph thru Idaho last month. Going along just fine and then started slowing on a fairly minor hill ... gave it more throttle and it wouldn't accel until the secondaries on the q-jet kicked in. This problem immediately became chronic and has not improved or gotten worse in 835 miles of limp home driving. Anyway, I turned around and limped the 835 miles back home to Oregon on what I later found to be 5 cylinders firing. At the time of the occurrence I replaced both the carb and chassis fuel filter, plugs, plug wires, cap & rotor. No help at all. Once I got to where I could do something more I found the following:

150# compression on all 8 holes (less than 5# difference across the board)

Pulled plug wires one at a time at the distributor and found #s 2, 5, & 8 getting plenty of spark but did not change rpm at all. I then pulled all 3 wires off and to the side ... so with only 5 wires connected the rpm and performance stayed the same.

Starts right up and idles o.k. with 18 inches of vacuum in neutral. Vacuum drops to near zero on any application of throttle. No flutter at all on vacuum guage needle at any time. Believe it or not I can cruise at 60mph showing 5" vacuum and even accelerate somewhat by flooring the pedal to kick in the secondaries, and still got 4.5 mpg. (8 normal)

Anyway, one final note ... about 500 miles into my return home the smog pump rail on the left bank burned a quarter size hole where the 4 small tubes join the larger pipe. Nice noise for the next 7 hours ...

Any thoughts on cause of power loss?

... I have not done anything else as yet ... not even pulled the burned smog rail. (thanks to posts on this forum I now know to use #5 for checking timing from below).

Thx, Bill & Kitty

Hmmm.. this bears some thought. Compression numbers are excellent, best you could hope for

Since you have spark and compression on the weak holes, we're left with fuel as the missing ingredient.

Cylinders 2,5,8 aren't on the same side... otherwise I would suspect a blockage somewhere in your manifold passages, or exhaust.

Considering the apparent back pressure in the exhaust have you checked for a stuck heat riser valve? Is it on the driver side exhaust manifold, consistent with your left side smog rail leak?

The excessive idle drop with throttle also points to restricted flow somewhere. (can't breathe!) Is the exhaust system flowing well? Check the tailpipes for even output?

I will think some more.. good luck.

Had a chunk break loose in the catalytic converter on my 87 Jeep a couple of years ago just as i was getting off of a freeway. Car died and would not start again due to back pressure,......Had it towed to a shop and when they hit the key it fired right up. They knew there was something wrong so they checked out a few things and found the problem. Turned out that loading and unloading the jeep on the flatbed moved the piece in the cat enough to allow it to fire up.

I don't think the 87 RVs had cats.. I think that started in 1990 for most RVs and trucks. Plugged exhaust is definitely a possibility.

The heat riser I mentioned is a plate valve which "normally" is wide open when warm, but may have become stuck. Also, even more weird, I once had the valve plate break loose from the shaft and lodge downstream, blocking the muffler, with symptoms similar to yours, except intermittent when the loose piece bounced around.

Check to see if an exhaust pipe hanger broke, pipe got kinked?

Hmm. let us know what you find!

Thanks for the ideas so far ... My heat riser weight moves freely but in the next day or so I will check timing (now that I know about using #5) and also if the heat riser moves as it should with temperature rise.

( Amazing how not enough knowledge can send us astray. I was convincing myself I had a jumped chain when checking timing from below using cyl #1 and not even seeing the balancer mark show up)

You are correct, no cats on the '87 ...but duals with a balance pipe before the mufflers.

If timing and exhaust problems are not noticeable and given that the problem is apparent from dead cold up to normal operating temp, I have a couple other things kicking around in my cranium ... I had a vacuum whistle that came on strong for about 10 minutes worth of driving about 500 miles before this issue began. By the time I could pull off the road safely it was gone and never came back.

Vacuum issue in A.I.R. system?

How about bent intake pushrods (unlikely on 3 cylinders at once I think, especially at fairly low revs ... 3800@55mph)?

Thx, Bill & Kitty

quote:

Originally posted by fleecerdog:

Pulled plug wires one at a time at the distributor and found #s 2, 5, & 8 getting plenty of spark but did not change rpm at all. I then pulled all 3 wires off and to the side ... so with only 5 wires connected the rpm and performance stayed the same.

That can introduce a new problem. The HEI does not like to operate without a path to ground for each cylinder. It can wreck the coil, module or the cap.

That type of testing is best done by shorting out each cylinder. I made a board with 8 doorbell buttons, each leading to an installed plug nipple. I just stick a bare end of the wire in the nipple and put it on the plug. I believe there is a GM tool for that purpose.

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Have you checked fuel pressure while driving?

Are the dist counterweights free to move and spring back?

Worn out cam????

Thanks on the HEI info ... now I have to be careful too? I'll be sure to post what I find after tomorrow ...
On the flat cam ... maybe, we'll see. But that would be in the same classification of probability as lifters or pushrods, i.e. what are the odds of 3 flat intake lobes for intake only, all at once? If exhaust lobe, lifter, or pushrod went bad I'd have extreme carb backfire, which I don't. Or am I missing something (as I sometimes do according to Kitty).

Thx, Bill & Kitty

I'm still thinking some kind of obstruction... the sudden coincidental onset doesn't sound like a wear related failure.

AIR system just pumps air into the exhaust to dilute the pollutants, contributes to back pressure but shouldn't do anything when it fails...

Interesting problem, good luck.

It really sounds more like a fuel pump problem - the GM pumps are good for around 50K miles.

Blocked Muffler?

Could part of the interior of the muffler have been rusted out, broke and stopped some of the exhaust flow?

Or collapsed exhaust pipe?


Or the sock filter in the tank.....typical symptom is the vehicle goes slower, slower and slower or won't accelerate past a certain speed or rpm....

Thanks so far for all of the helpful responses.

One piece of good news is I did find the vacuum actuator had disengaged from the heat riser ... c-clip gone. I put that right but by the time I found that issue, I had my A.I.R. rails off (from the burn thru mentioned earlier). Until I can find some plugs for the exhaust manifold to replace the smog rails I don't want to start the engine.

Anyone done these ... they are close to 1/2" npt but not quite ... I'm going to try and find a 3/4" sae fine plug to see if that works ... nothing that big in my local hware or Lowe's.

Reminds me of a problem we had with a SOB in 2005. Tere was driving it to Tennessee and decided to see how fast it would go and at some point the thing just died. Had it towed about 100 miles to a Ford dealer since it was a Ford 460, normally aspirated, and after several hundred dollars of diagnostic work, they said it was probably a whichamacallit in the thingamajob. At that point, towed it to my son-in-law (aka jet pilot/airframe mechanic) and he figured it out in 10 minutes. Clogged catalytic converter. Took it off, reamed it out with a rebar, put it back on, ran fine. Cost? Zero!

quote:

close to 1/2" npt but not quite

Any chance it is metric?

May be regular household plug or SAE?

quote:

Originally posted by fleecerdog:
Thanks so far for all of the helpful responses.

One piece of good news is I did find the vacuum actuator had disengaged from the heat riser ... c-clip gone. I put that right but by the time I found that issue, I had my A.I.R. rails off (from the burn thru mentioned earlier). Until I can find some plugs for the exhaust manifold to replace the smog rails I don't want to start the engine.

Anyone done these ... they are close to 1/2" npt but not quite ... I'm going to try and find a 3/4" sae fine plug to see if that works ... nothing that big in my local hware or Lowe's.

If there is any tube left on the AIR rails, they can be crimped shut. Otherwise, the AIR nuts can be welded shut at the top or threaded for a pipe plug in each one. If they are hard to thread, they needn't be perfect. They can be threaded enough to get good thread engagement, and then sealed from inside with hi temp exhaust cement.