Misfire under load

DonD · June 09, 2014, 07:39 PM

Must be contagious. Mine is showing classic fuel starvation on a trip we're on right now, a steady pull for an alt. gain of 1700ft in about 40mi.at 90 degrees.
N
She has new fuel filters, plug wires, rotor, cap and coil. Looks like measure and cut an access under the bed when we get home to R and R the pump.

DonD · June 12, 2014, 12:25 PM

Did some pre measurements and the new access hatch will be in the hallway in front of the toilet room door. No need to remove the bed! AZone has the pumps so the way home I'll stop in and get them.
I'll repl. both pumps and the spark plugs, that should have her humming.

Heading for home tomorrow, all downhill W%

cncsparky · June 12, 2014, 02:13 PM

Don, my suggestion is to make sure you get a good pump. You don't want to do this job twice! I chose an OEM ACDelco/Delphi pump for mine. O'Reilly had them. Same with the mechanical pump. Heard too many bad stories about lesser brands ie Airtex etc.

DonD · June 12, 2014, 02:51 PM

Yep, GM ep 386!

DonD · June 13, 2014, 05:23 PM

Home again. The Bus ran perfectly in the same temps as going to the CG on Monday. The only difference was just for grins I loosened the gas cap to see if maybe it's not venting properly.

I still plan to R n R the pumps but...... Hm?

Guess I should begin my own thread

M & J · June 13, 2014, 05:59 PM

Highly recommended Don.

newrvguy · July 21, 2014, 01:33 AM

HI all great information here I sort of have the same problem....1987 P30 454 Pace arrow ran fine and great had a small exhaust leat just re tightened the three bole from exhaust to manifold re started and now when i push on the gas almost stalls out...like a miss or something HELP have a trip this weekend?

Rambunctious · July 29, 2014, 11:04 PM

Okay sorry for my delay in getting back to my post. Here is the latest. As it turns out. My left muffler had collapsed and no exhaust was coming from it. I passed the CA emissions today and tomorrow I'm replacing the mufflers. I'm guessing my catalytic converter and exhaust system was getting red hot with a stopped up muffler. I'm betting that this is causing excessive heat and causing my misfiring under load via a vapor lock..
I will post the results of the after muffler replacement test drive tomorrow.

Rickf1985 · July 30, 2014, 09:50 AM

You passed Ca. emissions with a plugged muffler!!?

HOW? Plus that would have been sending all of that exhaust through the crossover in the manifold to the other side, I can't believe it did not overheat. The gas had to be boiling in the carb.

legomybago · July 30, 2014, 11:40 AM

Im not sure I've ever seen a catalytic converter on a carburated rig...must be a CA rig i??

GONMAD · July 31, 2014, 08:31 AM

Plenty of rigs & autos came with cats. They are as worthless as A.I.R. pumps which only increase the PPM,s. Cats only finish burning the unburned fuel left by insufficient ignition of the charge in the combustion chamber. The Fords are notorious for melting the palladium media & closing up the exhaust. I've happily removed countless cats when changing exhaust systems & coupled with a 'GOOD' aftermarket ignition system have had no more problems. I'm blessed with not having the smog laws that Cal. has thank God. When I HAD to install cats on something I used aftermarket hi flow DUAL cats which reduces the excessive back pressure that ONE cat produces. The heat will still be present but they won't melt like only one will. I hope this helped some. C YA! GONMAD

legomybago · July 31, 2014, 10:43 AM

Did cars and trucks use cats without O2 sensors? The big three leaned out their carburated engines so far they ran hot, no power, vacuum nitemares (our wonderful American 80's cars). Then fuel injection was put in with O2 sensors, MAP sensors etc. and we then began to see the turn around...I need to google this I guess Hm?

cncsparky · July 31, 2014, 10:52 AM

Yes, Cats predate electronics as well as O2 sensors.

legomybago · July 31, 2014, 12:03 PM

Well, I learned something today

Rambunctious · July 31, 2014, 09:05 PM

Quote from: Rickf1985 on July 30, 2014, 09:50 AM
You passed Ca. emissions with a plugged muffler!!? HOW? Plus that would have been sending all of that exhaust through the crossover in the manifold to the other side, I can't believe it did not overheat. The gas had to be boiling in the carb.

The mechanic was able to get readings from the working muffler.

Yes it was getting hot. And I was experiencing misfires or prefires. I hope this solves that. I will be back after the mufflers are on.

newrvguy · July 31, 2014, 11:49 PM

Great posts everyone learning so much... Should I try to reloosen the exhaust to see if the misfire goes away? I'm in CA as well as you are.

Froggy1936 · August 01, 2014, 11:52 AM

The first catalyitic convertors were used in 1975 . Frank

Rickf1985 · August 01, 2014, 08:42 PM

Newrvguy, get yourself a laser heat gun and check the temp of the pipes on both sides and see if they are the same. The drivers side will be cooler for a while during warm up if you have the EFE system. You can tell because there will be a valve with a vacuum line going to it with a long rod attached to a butterfly valve at the manifold to pipe junction of the drivers side exhaust. A lot of times this will freeze in the closed position and send all of the exhaust through the manifold all of the time, this is bad. Other times it will freeze open and never send it through the manifold, this is good as long as it passes inspection. To see if it works watch the rod as someone starts the vehicle when it is cold, first thing in the morning. It should move to the closed position. If it does it is working and it should come off as the engine warms up. You can follow the vacuum line up, it is a metal line along the top edge of the drivers side valve cover, and plug that line. That will prevent that from functioning.

Rambunctious · August 04, 2014, 03:34 PM

Quote from: cncsparky on May 27, 2014, 05:52 PM
How old is the cap/rotor? Anytime I had a misfire under load in other vehicles, it was something to do with ignition. However, vapor lock can be an issue in these RV's so good to go through the fuel system too. Especially since you mentioned it running hot.

What plugs did you put in it?

I put AC delco cold plugs in with premium wires with heat sleeves I'm going to change Dist cap and rotor but I have a feeling it may be a bad fuel pump. I've changed all fuel filters rebuilt the carb and last week I put on new mufflers because one was completely blocked. I thought that would fix it. My RV is running cooler and sounds perfect but at highway speeds only...under load it still misfires... i?? I also just passed the CA emissions test and the RV runs up hill at lower speeds just fine it's on the highway under load only. My shop keeps telling me on the scope everything looks picture perfect. I'm going to pull all of my hair out.

cncsparky · August 04, 2014, 10:52 PM

Quote from: Rambunctious on August 04, 2014, 03:34 PM
I put AC delco cold plugs in

You went with a colder than stock plug? What is the plug number?

MotorPro · August 05, 2014, 07:41 AM

Why did you put in colder plugs? Not a good idea in this application.

legomybago · August 05, 2014, 10:38 AM

After you run it down the road and make it misfire, what do the spark plugs look like? Does your carb need to be fattened up? (running lean)? You may need a complete new dizzy....with coil.

newrvguy · August 08, 2014, 12:46 AM

Thank you Rick I will check to see if I have that rod and also check to see the temps on both sides of the exhaust this weekend. I will keep you informed!!

Rambunctious · August 09, 2014, 02:29 AM

QuoteYou went with a colder than stock plug? What is the plug number?

AC 19307138 plugs...

Rambunctious · August 09, 2014, 02:41 AM

I replaced my distributor cap and rotor...heavy build up on number 7 contact inside the cap but the rest of the contacts were clean...rotor looked ok but switched it out anyway. Still a misfire under load. Highway speed only. It must be vapor lock. I think my fan clutch is bad. I still need to cool this thing down some more. I'm going for new radiator thermostat and fan clutch Hm?

I'm on a mission now. My wife had to drag me into the house after midnight last night.