Help - MH Can't climb hills

[swebster]

We left for CT on Friday and what should have been an easy twelve hour trip over two days turned into a three day ordeal chugging along at 10 miles per hour at times in the breakdown lane.

Here's what happened:

Left Louisville and about 200 miles into the trip started noticing a little hesitation at the top of a climb. Nothing big but noticable. Another 200 miles into the trip and we could barely climb a hill. Speed dropped to 10 - 15 and made it to a Flying J in the breakdown lane. Getting lots of misses, back firing from the exhaust, hardly any power.

At the Flying J I called a great friend who is also a great mechanic and he said to check and replace the coil, modulator and pickup. I did that and replaced the cap an rotor as well. By now if was 10 so we camped a Flying J.

The next day everything was great. Pulled hills with no problems made it to NJ...then it started happening again. By CT is was getting hard to maintain 45 on gradual uphills.

So we made it to our destination but obviously something is wrong. I've done the following in the last few weeks:

New front mech fuel pump
New rear elec fuel pump
New filters inlin and at carb
Headers with complete exhaust installation
Replaced all vac hoses (I've rechecked these about a millions times)
New magnetic switch for ignition to starter
New wires and plugs

I did notice a spliced wire into the 12V lead side of the ignition which I have yet to trace. But does anyone know why I'm slowly frying my ignition?

Any other ideas on what it might be? Advance, something electical? Does an under voltage situation cause this? Shorts in the ignition ciruit? I'm open to checking everything at this point.

[smily]

I had same problem but mine was burnt plug wires. Manifold heat was cooking them while enroute fromt the Gulf Coast to East Coast. Replaced them three times while en route. about 600- 800 mile a set. Now I have heat shields and I am getting about a thousand miles from a good set. I guess I will have to bite the bullet on a set of Jacobs but before then, I am going to install a shroud that will direct air onto the passenger side of the engine to cool the manifold, plug wires and anything else I can get some air on to. I read about this retrofit in my Chevy P-30 repair manual.

Smily

[thenewkid64]

Steven,

Check the vacuum advance in the distributor. Mine on the 76 seized. It would do the same thing. Once I had the Distributor replaced it was all good again.

Before the distributor was replaced the unit idled fine, under load it was chitty chitty bang bang.

[fritzs]

Steven - You didn't mention much about your motorhome; i.e., make, model, engine, etc. so were all guessing somewhat in our attempts to help you. Being that it's an 86 model year, probably carbureted, and that you've replaced a lot of the other things already. . .here's a suggestion. If you backfired even once with a carbureted engine the power valve is probably all carboned up with soot and sticking. A sticky power valve will also cause the types of problems you have mentioned. The "missing" sort of leads to bad wires and stuff (or ignition anyway), but lack of power could be that power valve situation. On Chev engines it can be fixed without removing the carb, just the top cover (extremely carefully), polishing up the power valve piston, and replacing. Do you have a Chev with Quadrajet (like a 454 engine perhaps?) This is probably too late a reply, but what the heck. . . .best wishes!

[87MH]

Stephen:

Here are two more possibilities.

I encountered a problem once in that the electric line to the rear fuel pump first goes through a controller (on/off) operated by oil pressure, (on the schematic, anyway, couldn't trace the line on mine), and I lost the +12 volts to the pump about a mile from the house (it appeared to be an intermittant problem). After limping back to the house (symptoms similar to yours), I "hard wired" the fuel pump into the ignition switch (switch on, rear fuel pump on). I plan to install a Fuel Pressure Gauge on the panel, possibly do away with the mechanical fuel pump - still have an issue with the genny - I think fuel related - will try a fix involving an in line fuel pump to the Onan.

Second possibility - there have been some discussions about internal filters or screens on the fuel pickup inside the gas tank - just a thought - trying to come up with "things" that might manifest themselves only during intervals of high fuel demand.

Luck.

[ALANSD]

last week a guy told me about a similiar problem with his P30 Holiday Rambler 454 also. He took off the gas line and blew air back through the pickup screen on the gas tank intake. Cured his problem. In my opinon if that cured it , it would be tempoarary until the screen got dirty again. Can you chek the gas flow at higher than idle rpm to see if that is an issue?

[59toaster]

Choke.

Make sure it's open. It will give these symptoms if it starts to close while running. THose heating elements start to burn out after a few years. I find I only get about 2 years out of the Autozone ones.

[swebster]

Well thanks for all of your replies. Sorry I didn't mention the specifics earlier I has just asumed everyone knew my beast already; its an 86 AS MH Classic on a P30 with a carburated 454 (QJet) and stock HEI ignition.

I'll check the carb (power valve) tomorrow but the backfiring and missing seems ignition related to me. Also the fact the I after replacing the internal dist parts it ran fine. I also saw a drop in MPG from an average of 8.5 before the headers to 7.5 on this trip (when I expected to see an increase) all seems to point to lack of spark.

I replaced the rear fuel pump, check 12V to the leads, change the filters, changed the carb filter, did an idle fuel delivery check (plenty of fuel), check the fuel lines for kinks, leaks, anything.

Also have brand new wires and plugs with the heat sheild re-installed inbetween the headers (after some slight mods with a ginder). I rechecked the wire as well on this trip at each stop since so much was new up there.

Choke was open. I ran for a while a 15 mph up a hill with hte doghouse and air cleaner off looking for fuel delivery, and to eliminate the possibility of flapper door on the air horn closing.

I did find one vacum leak (the line to the gauge sender was off) but while reconnecting it made my gauge work again, it did not solve my issue.

Brett - I was thinking about the advance as well. I'll see if I can replace that tomorrow. (It and the pick up still in the box) are the only things left in there to replace).

I'm also suspicious of that "extra" wire into the 12V lead on the dist. Anyone ever had issues with an under voltage or short to the dist "frying" something? The reason I ask is that the brand new magnetic switch for the starter broke it's mount and shorted to the oil fill tube. I didn't know if this could cause an issue.

[overlander63]

Steven, check the coil, if you see carbon tracks on it, replace it. It is very possible after it gets hot enough, it starts breaking down internally. It will still give spark, but much diminished, and sometimes not enough to ignite the fuel.
Does your engine have a coil-in-cap, or is it separate?
Let us know what finally fixes it, you never know when we may need the info.
Terry

[swebster]

Terry,
Yep...thought that too so I replaced it when we finally broke down. The new ignition parts worked great then got worse and worse again.

I'll keep working on this and post whatever fixes it. I guess I need to fix it if I want to get back home. How's that for motivation?

I have a theory that I'll test tomorrow. I'm wondering about the low voltage into the ignition because I think it could actually be an alternator issue. In that I mean what would run great after an night on generator then slowly, gradually decline over 100's of miles? I noticed on this last one that the dash voltmeter started the day at just above 13 volts but was closer to 12 by the end of the day. (Only getting 10 at idle) so I'm wondering if I'm running at some percentage off of batteries in a partial charge from the alternator situation. So after a few hours like this the voltage drops to the point where the coil begins to break down.

I'm not too knowlegable on how coils and ignitions work however so I don't know what an under-voltage situation will do. Will the coil slowly break down or is it kind of a binary thing...enough voltage and it works, not enough and it just stops? This I don't know. I had something similar happen to me in an old Mercedes in the Badlands (SD) and it turned out to be an alternator.

My testing tomorrow will be to run the MH up and down some local highways with two wires coming off of the chassis battery into the coach and another form the 12V into the coil. That way I can get accurate voltage readings underway and as the missing begins. I figure this is the only way to tell if this problem is something going into the ignition or something in the ignition.

I have a brand new alternator in the baggage compartment just waiting to go in so I may just replace mine either way if only for the removal of one variable.

Whatever happens....I'll keep you posted.

[garry]

Extra wire on Dist could be for a tach.
Sounds as if you have eliminated just about everything, hope the alternator does the trick. I had the same problem and mine turned out to be the coil but you eliminated that. Do you have a droping resistor to the dist?? Don't think you should have but if someone had a MSD or Accell in the past they could have installed the droping resistor.

Garry

[85MH325]

Steven...

Garry beat me to it: the tach on my 85 325 ran from the distributor, just a single wire.

Just another thought... new parts do occasionally fail; although perhaps not very often, you might want to consider another coil. It may just have been that you got a 'bad' new one.

Good luck!

Roger

[swebster]

Yeah..one in for the 12V and one back out for the Tach. The 12V in is the one with the "Splicer" on it. Very suspicious looking. Pretty sure GM didn't use those blue snap splicers from Radio Shack so I could be chasing an old problem with voltage to the coil. No resistor (yet).

Feel like this one could be the "puzzler" on Car Talk next week.

[BReed]

Steve,

I experienced this problem years ago in a class c motorhome, seems to me the engine was a 454. What we determined was the catalytic converter was plugged. The mechanic drilled two holes in the exhaust pipe preceeding the coverter of course and the problem was temporarily solved. Hope this helps in your trouble shooting efforts. We were stuck in New Hampshire in the White Mtns. and I'm from Michigan.

Bruce

[fangthorpe]

Do you have an aftermarket tach? I have seen a bad tach pull the ignition down at high rpm on a racecar.

[overlander63]

Originally Posted by BReed

Steve,

I experienced this problem years ago in a class c motorhome, seems to me the engine was a 454. What we determined was the catalytic converter was plugged. The mechanic drilled two holes in the exhaust pipe preceeding the coverter of course and the problem was temporarily solved. Hope this helps in your trouble shooting efforts. We were stuck in New Hampshire in the White Mtns. and I'm from Michigan.

Bruce

Bruce, steven replaced his exhaust system with headers before he left. I am thinking he, um, eliminated that potential problem.
Steven, you could have a bad ignition pickup, or module. Mid '80's modules on GM were prone to failure, although usually they just stop working altogether, but could be the same problem, it gets hot, and starts sending faulty signals to the coil. If you replace this part, be sure you put dielectric grease on the part that rests on the distributor housing. It is located under the rotor, inside the distributor. The pickup is located in almost the same spot, but removal of the distributor and disassembly are required, probably would be better to replace the whole thing since you have to take it out anyway.
If you are near an AutoZone, or a similar place, why not drive it over and have them perform a free alternator test?
Long-distance diagnosis is kind of like computer tech support...
Only other thing I can think of for you to look at is to remove one of the plug wires from a spark plug, install another plug on the end of the wire, ground the base of the plug, start the engine, and observe the color of the spark. Blue is good, orange is iffy, yellow is not good.
Terry

[swebster]

No cats on this rig...pre-converter and your right in that its headers into 2 1/2 inchers all the way back

fangthorpe - your tach comment reminded me that I occasionally get a dead tach or incorrect readings. Like 1200 rpm at 65 mph then it bounces back up. Could be a trouble spot or a short. No tach changes when it's misfiring. I was getting blue when I pulled a wire at the cap but at idle under no load it runs fine.

Terry - I did buy a new pickup so I might try replacing it as well. Thinking I should have just bought a new dist.

This is going to be a fun one.

[shelocta]

I've been having similar problems on a trip from Texas to Florida. Can’t tell you about hill climbing because there were none. Change the carb fuel filter and it ran well for about 300 miles then started acting up. Pulled filler and took you the check valve and replaced filter. Ran good the last 1000 miles. Had it out about a week ago and the problem it back. Read on other forums this was a fix? I'm thinking seriously about converting to a Holley TBI.
Good luck in your hunt.
Bill

[85MH325]

Originally Posted by swebster@myrvadvanta

fangthorpe - your tach comment reminded me that I occasionally get a dead tach or incorrect readings. Like 1200 rpm at 65 mph then it bounces back up. Could be a trouble spot or a short. No tach changes when it's misfiring.

That would be your "blue splice" causing your dead tach. I had similar problems with mine which was how I found where the tach ran to. It merely caused a dead tach, though... no driveability issues. I think I put a new connector on and once the bad connection was cured, it had no more problems.

I have to agree with Terry about the diagnostics... if the simple stuff doesn't fix it, it's probably time to head to someone with diagnostic technology...

Roger

[ALANSD]

thought of another issue--- PeterH had replaced his igniton module awhile back ,and the new one as I recall was bad out of the box, left him low on power also....just another thing to look at.