Getting our 1989 Winnebago Warrior 22EC ready for the road...

[engineer bill]

Mechanic says he's inspected wires, plugs, all distributor functions and he's stumped. No-Charge.

[Rickf1985]

You are absolutely sure the backfiring is into the exhaust under acceleration? About the only thing that will cause that is a burnt valve but a burnt valve will not go away under other loads. The only other thing that will cause it is ignition cutting out and loading the exhaust with gas and then cutting back on and lighting it off. Bad switch, bad coil, bad module. Lean condition, jumped timing, both will cause backfires through carburetor. Wrong firing order could "possibly" give that symptom but that is a real long shot. Easy to check it though, 18436572. Make sure none of the plug wire run against each other side by side, they can cross at an angle. Side by side touching will cause cross firing through induction.

Reading over your post several times I just keep seeing "missing and stumbling and backfiring" That is all the symptoms of a bad coil. especially since when you slow down it "settles down"

[engineer bill]

(More specifically or perhaps clearly)
Backfiring into exhaust manifold and/or muffler.
With all three of these happening or happened,

1. Only when really warmed up, after a couple hours driving
2. Only when accelerating right after deceleration or stop
3. Hard acceleration-with vacuum gauge needle < 6 or so.

[Rickf1985]

With all the other things you have done and the limited things that can cause that type of problem the coil is about the only thing I have to offer right now that does not entail fairly extensive testing of the mechanical systems. After that I would be looking at weak or broken exhaust valve springs, A binding exhaust valve. Let me ask this, is your emissions and timing system all set up completely stock? Do you still have the vacuum advance set up on ported vacuum? I really don't know where I am headed with that yet but just gathering info. I am looking at a vacuum related possibility but I am just not seeing it. On low vacuum/ hard acceleration the EGR is supposed to be cut out but something you can try is to unplug the vacuum line from the EGR valve right in front of the carb and plug the line. Run it like that for a while, it will not hurt anything but it may ping a little, it may not. The other vacuum related item is the A.I.R. pumps which will be engaged at that time and pumping air into the manifolds. Now if the ignition is cutting out which would cause the stumble you feel then there would be gas in the manifolds and the air from the pumps would mix with it and the flame from the cylinders that do fire when it comes back online will light the whole mess and bang. I keep going full circle to the ignition.
If a coil is going bad then it will go open circuit as it heats up which it does normally in use. The faster the engine runs the harder the coil works since the ignition is firing faster. As  you slow down the coil cools down and the wires reconnect and it fires again. A lot of the time this pattern will get worse and worse until it just will not run.

[engineer bill]

Rick, You've given me plenty to think about check out and thanks for that. Changing the coil is cheap and easy and so a no brainer. I'll report back in a few days.

[engineer bill]

The bushings in the distributors on these are notorious for short life-they get no oiling. Check for lateral play at the rotor (it first manifests itself as arcing in the cap). On the plus side you can buy a complete assembly including module and coil for around a hundred bucks.

Great suggestion. I wonder if I can substitute a generic distributor and not run astray of the California smog requirements?

[Rickf1985]

The distributor is not part of the emissions equipment so it would not be a problem but do not cheap out to much on that area. As long as you stay with a GM HEI style distributor they will not notice. And remember that a lot of the aftermarket distributors are set up for performance, you need a stock one for the emissions, verify it is stock curve before buying it.

[kansascat]

Hope its not doing what my 79 P30 is...after running a fair distance down the highway its exhaust is heating the fuel line from the rear tank to the point of basically causing a vapor lock situation. Thing is lean fuel mix i wouldnt think would cause backfiring, but other than that part the running condition sounds very similar. Let us know what ya find out.

[Froggy1936]

Why dont you move the fuel line to the outside of the frame ? Copper or steel line is best, But can be done with hose also ! Frank

[engineer bill]

Vacuum Advance hose connected to "Ported Vacuum" for this application, right?

[EldoradoBill]

Probably. But they are different year-by-year. Some go through a thermo valve first, some connect to manifold vacuum. What's the sticker on the side of the air filter housing show?


Bill

[Rickf1985]

Yes, BUT, as Bill said, it is through the TVS (Thermal Vacuum Switch) on the thermostat housing and they have been known to fail. The TVS is the one to the left sticking up out of the top of the thermostat housing. The complete emissions vacuum diagram is on the air cleaner housing.

[engineer bill]

All great information.


My diagnostic observations have evolved a little bit. Here's a summary of where I am now:


A. Backfiring into the exhaust,
Can't tell for sure if both sides or just right side? Need to find an observer!
B. Only when thoroughly warmed up.
C. Only with very low reading on manifold vacuum gauge. High load-big hill or rapid acceleration, up hill on ramps, ?? % grades. Carb secondaries nearly fullly open?
D. Manifold Vacuum gauge reading is 0-5 in hg
E. Stops backfiring when I ease up the gas pedal till vacuum climbs to back up to 6-7 or so.
F. I can't keep up with hilly traffic the after fully warmed up.
G. In general, not running as strong as it used to, even on flat city streets. Timing?


I've been reading up this weekend on the Emissions Control Systems (1989 CA Spec.) in the Chevy Motor Home Service Guide, looking for vacuum related systems that might affect timing or mixture changes under very low manifold vacuum)


Here's what I plan for the next couple of days:


1. Check for exhaust leaks, especially on right side.
2. Check the timing.
3. Check Vacuum Advance with vacuum pump and observe with timing light. I now understand. It actually reduces advance under high vacuum condition-in this case ported vacuum-from above the butterfly plates. I've got to admit I don't really understand ported vacuum particularly well. Some vac at full throttle and essentially no vacuum with throttle closed? Some Specs use manifold vac for Vacuum Advance and some specs use Ported Vacuum... My CA Smog spec has ported vacuum advance and minimal advance at idle, 4 degrees.
4. Check EGR function & plumbing. + TVS
5. Check A.I.R. pumps, diverter valves, check valves, hoses, especially right side.
6. Check H5D option A.I.R. electronic pump Control Module, note: Check Engine Light is not doing the bulb check on start up.
7. Check fuel pressure at idle and at full load. Could be tank pickup screen, electric fuel pump in tank, regulator, frame mounted filter, hot tube, mechanical fuel pump, carb, etc. Thinking about installing a fuel pressure gauge on dash anyway.
8. Replace all vacuum hoses, one by one.
9. Check spark plug gaps vs. spec.
10. Check fuel line not run inside rail near exhaust.

10. Don't know. It's unusable in it's current state despite pouring at least $15-$20,000 into it last couple of years including a really nice toad setup.


BTW: Have recently replaced spark plug wires, cap, rotor, e module. Also fixed a couple of obvious leaking vacuum hoses.


So, that's my tentative plan, pending input from the members of this awesome group.

[engineer bill]

TVS (Thermal Vacuum Switch) on the thermostat housing and they have been known to fail. The TVS is the one to the left sticking up out of the top of the thermostat housing. The complete emissions vacuum diagram is on the air cleaner housing.

Add TVS to list of things to checkout.
Thanks Rick.

[EldoradoBill]

Short the A-B terminals on the under dash ALDL connector and see if the check engine light comes on and gives you codes. If the light comes on and gives codes then you have a PCM issue that needs to be addressed first. If still nothing time to get the bulb or its circuitry fixed or pony up for a GM Tech 1 scan tool (currently around $300 on eBay if you can find one).


Backfiring under heavy load could be a lean condition but checking for stored codes would be my first step.


Bill

[Rickf1985]

No OBD on these. Good old fashioned non computer carburetor with emissions. Old school stuff to some, not so old to others (Like me) W%

And backfiring under load into the intake is a lean condition, he is getting it into the exhaust under load which to me is a valve timing condition.

[engineer bill]

backfiring under load ...  into the exhaust ... is a valve timing condition.

Let's hope not.


reminder btw: it runs pretty good under all other conditions. Even ok under big load if I back off the gas pedal and allow the manifold vacuum to rise up into the 6-8 range.

[engineer bill]

I've been studying the book on the Emissions Sub-systems and trying to figure if any might cause this:
- Timing per Emissions label,
- Vacuum Timing working properly and connected to ported vacuum not manifold, 
- EGR, and TVS
- AIR Pump Diverter Valves,
- PVC valve connections leaking,
- Misc. leaking vacuum hoses
[feel free to correct me here or add anything]

I wil try to check these out but first I want to check:
- firing order,
- plug wire routing and
- spark plug gaps


My mechanic buddy is getting really tired of seeing me come in with the Winnebago. Since it only happens when the engine is good and hot, he can't see/hear the problem sitting at his shop. I can drive it up the hill and back but by the time I get off the highway and drive the two blocks to his shop. Nada. Last time we spoke he suggested selling '89 Winne Warrior and buying his '94 Fleetwood Flair.  :)rotflmao


It think I may take it back to the really expensive guy. But first I'm going to take a quick look myself. Not today though-it's supposed to be over 100 here.

[engineer bill]

No OBD on these. Good old fashioned non computer carburetor with emissions. Old school stuff to some, not so old to others (Like me) W%

My '89 seems to have the "Check Engine" light but has no diagnostic connector under the dash. (I've been rooting around under there for months now and I'm pretty sure I would have seen it.) The auto makers were pretty busy trying to comply with the new emissions law back in '89. I know because at that time I was working at Peterbilt as a design engineer on wiring and diesel engine controls  The situation was complete chaos. I wouldn't be terribly surprised if the change order for the light got in but the connector and/or electronic control box did not.
Of course a quick look at the Diverter Valves (electric or vacuum powered) should show for sure.

[Rickf1985]

The check engine light works off of the air temperature sensor plugged into the drivers side of the air cleaner. It is basically useless. I have NEVER seen it come on except for when it was unplugged. Actually plugged in but a few other things in the system unplugged. Ten tree huggers in Cali. just died reading that. :)rotflmao :)rotflmao

I don't think any of the emissions controls are going to cause that problem but by all means check them out. I thought you had already gone over the plugs and wires and firing order! The firing order would definitely give you that problem but under much lighter load. Two plug wires running parallel and touching is a definite possibility through cross firing but 9 times out of 10 it will backfire through the carb. You could be number 10 and have just the right combination. Plug gap and or wrong heat range plugs are a real possibility, as the toad increases to full load it takes a hotter spark to keep the plugs from fouling with the amount of fuel that is rushing in.

[engineer bill]

Rick,

I paid someone to check all that but ... I'm going to re-check what I can myself.


The mechanics have replaced the entire ignition system over four separate visits.

[engineer bill]

The check engine light works off of the air temperature sensor plugged into the drivers side of the air cleaner.

Great stuff.

[Oz]

This board, as the description states, is for people to share how they did their projects so others can learn from it, not for asking to help fix all your issues in one topic. The 9 pages of discussion has not met the board description criteria so it is now closed.

Please ask your different "how do I fix this" questions on the corresponding boards.