shoemaro Posted March 3, 2015 Share Posted March 3, 2015 I have an 89 YJ 2.5L that gets around 8-10miles per gallon, puffs out black smoke when you rev it up. At one time I had a kinked fuel line, fixed that, now getting the proper fuel pressure. Engine idles good feels flat getting past 45mph. I have changed every sensor on this. Cannot seem to figure out. No vacuum leaks, changed exhaust/intake gasket (did not see a crack in exhaust manifold). One question, I can put my hands over the throttle body with the air filter disconnected, it will not kill the engine, engine does not even stumble? Any thoughts? Could EGR valve cause an extremely rich mixture? Quote Link to comment Share on other sites More sharing options...
Administrators Moses Ludel Posted March 5, 2015 Administrators Share Posted March 5, 2015 Hi, shoemaro...You offer some good details, and the point that catches my attention is the hand over the throttle body. Obviously, the engine is getting air somewhere! So, your idea about the EGR is a possibility; the EGR would act like a vacuum leak of sorts if not seating properly. Other sources would be vacuum hoses or devices, including the check valve at the brake booster. The engine cannot run with your hand over the throttle body air horn or throat—unless there is another air source. I'd try a few approaches. With your hand protected from heat and skin burns, and the engine idling, squeeze the EGR valve diaphragm from the backside of the device. If you hear a distinct change in rpm and engine smoothness, the valve was likely seating. If unseating the diaphragm and plunger has no effect on idle whatsoever, you have a valve that is not seating. Make sure the vacuum to the valve is ported, applying vacuum only as the throttle begins to open. If necessary, remove the EGR valve and see if the port and plunger can be cleaned up. Do not soak the valve in carburetor cleaner, that will ruin the diaphragm. You can soak the base/plunger as long as you avoid getting carb cleaner on the diaphragm. The vacuum booster check valve can be a unique source for a vacuum leak. The valve is a one-way check type. If it leaks, there would be a continual loss of vacuum—or source of air! Look for other vacuum leaks, and check the ISA motor and closed throttle switch. For vacuum leaks, one means for testing is the use of WD-40 (or similar lower volatility spray); with the engine idling, spray a mist at vacuum junctions, the throttle valve shaft and hose ends. (Do not spray at areas that could cause the spray to ignite!) Listen for engine speed changes. A very recent 2.5L topic had me posting a vacuum diagram for the 2.5L four. Use that vacuum diagram as a guide, and check over your vacuum circuit. A possible trouble spot is any vacuum reservoir or check valve leak, leaking vacuum lines, or a defective one-way valve. I like your focus. This does sound vacuum or air source related...Let us know what you find! Moses Quote Link to comment Share on other sites More sharing options...
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