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I have replaced the engine in my 1990 Holiday Rambler with a Jasper remanufactured. I have about 2,000 miles on the engine and it has developed a "backfire" problem when pulling hills or accelerating. Also, fuel economy has dropped from 7.5 on old engine to 5.6 on new engine and the new engine has less power. On flat I am still accelerating at 70, but on hills I drop to 25 - 30 mph. I don't think I would have sufficient power to tackle mountains! New engine was installed with new plugs, wiring, distributor, fan clutch, hoses, fuel filters, etc.
Shop has run computer diagnostics and has been unable to find problem. Any suggestions?
First suggestion would be to get a new shop. A 1990 should be a full injection engine. Did they put a new oxygen sensor in it? did they take the fuel pressure under the conditions that make it backfire? Did they check the exhaust backpressure? And, there is nothing to say that in 2000 miles it hasn't burned the boot off a sparkplug wire or two. Maybe it needs "another" new fuel filter. backfire and losing fuel mileage tells me that not all 8 cylinders are working.
I have an intermittent backfire which sounds like I am shooting ducks at around 2000 rpm. I have a points type distributor with a kit to make it electronic. I put a msd ignition module on but same problem. New wires (They burn alot on #1 with headers) new plugs gaped to.042 as someone said gap should be increased with msd. Crane cam 216 duration and.485/.515 lift, holley avenger 770 carb, and edelbrock rpm air gap manifold. Fresh rebuild but the heads are stock with 5/16" pushrods and competition cams magnum roller rockers. The package looks sweet in Viper yellow and a L-88 highrise hood, BUT it don't run worth of...
Any suggestions would be appreciated.
ps. Running shorty accel plugs equiv of 45RT
I'm assuming the shop did the simple things first---checked timing, firing order, fuel pressure and volume, etc. One thing you should look at is the spark plug wires for #5 and #7 cylinders---these are the rear cylinders on the left (driver's side) cylinder bank. At NO point should thes wires be close to and parallel to each other---crossing at right angles is OK--. The reason for this is that these two cylinders fire 90 degrees apart---720 dgrees( individual cylinder firing occurance per degrees of crankshaft rotation) divided by 8, (number of cylinders)= 90 degrees where firing order is 1-8-4-3-6-5-7-2, (#1 is front cylinder, left bank,then cylinder numbering is on left bank, front to rear;1-3-5-7, on right bank, front to rear is 2-4-6-8. As you can see, #5 and #7 are the only cylinders that are adjacent to each other that fire in sequence. The reason for seperating thes two spark plug wires is that, if they are close together and parallel to each other, when # 5 fires, the current in #5 plug wire will induce a current in #7 plug wire and cause ignition in #7 cylinder, but #7 piston is part-way up the cylinder on the compression stroke when this occurs which is definately NOT good. This can even cause melting of the #7 piston. The shop should run a comparative cylinder balance test which compares the condition of each cylinder(as determined by its power output)against the other 7 cylinders, this will give a base to work with in determining if you have a mechanical, fuel, or ignition problem.
My mechanic replace the points on my Gemini 82 holden and adjusted timing and stuff to try to fix a engine jumping problem and now it did a huge backfire and lost power, jumping all over the place, when I slowed down after running it for 70 kilometers. I had let it run too low on fuel before that and it started jumping then so i filled up, thats when the huge explosion occured out the back when I slowed.
One thing that comes to mind would be cam to engine timing or engine timing itself. By the sounds of things, your engine is "lazy." Even the best of rebuilders can make mistakes, or have defective parts. I would guess that if all the components were working on your old engine, they should work on the new engine. The gas milage indicates that your engine is laboring. After you check the wires and other things, you may want to have the base and cam timing checked. Have number 1 cylinder checked for TDC with a dial indicator and compare it with the timing marks on the vibration dampener. If that checks out, have the cam timing checked also with a dial indicator. This is a little more complicated, but should be considered. I have had new NAPA timing gears that came through improperly marked, so we always compare the old with the new. Have the shop connect a digital pyrometer to the exhaust pipe just below where the pipe connects to the manifold. Check one side against the other. See if the temperatures fall within the normal range on a test run.
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