Misfire, rough acceleration, ok idle? anyone?

[Rodeorulz]

1991 302 with 87k miles. It Idles ok, but driving down the road in a top gear I get a wicked engine shaking like driving with 7 cylinders. However when the truck downshifts, I have good acceleration and it seems everything is OK again. Any Ideas on crazy knocking / shaking while accelerating in Low RPM Range only?

[msafrit]

One thing to check you may not think of is the motor mounts. I just had the mounts replaced on my daughters astro van for the same symtoms. After replacing them, the engine is as smooth as ever. Hope this helps.

[Rodeorulz]

It runs so bad it feels like its going to stall and fall apart. However shifting into a lower gear feels fine with plenty of acceleration. Unlikely its motor mounts due to lack of power and HEAVY shaking in low RPM acceleration

[big_boy_toys]

check timing and vacum advance

[shady_tree]

98 f150 same prob misfire, xlr8s fine, gos into high gear no power lifters knocking, all spark plugs fire removed injector and switched around all of them work, passnger side #2 and #4 plugs are fouling out, changed cam and crank sinser no help. think its in the cpu the timing of the two injectors or the timing of the plugs? so im still looking

[mayville1]

Go to an auto parts store and have a scanner hooked up to it and check it out. Most of them do it for free.

[97chevyman]

well, take a compresion test on all of the cylenders. If you have a bad hole higher rpms will build up higher compression and make the engine fire. I think people need to start their own threads in stead of stealing someone elses, makes it more difficult. As for the 91, try some Marvels mystery oil in the gas, it cleaned out my chev, made my milage go from 10.6 to 15, no kidding. As for the 98, what engine do you have? . If your lifters are knocking at high rpms, sounds like it is really gunked up in there. How often do you change your oil? On your next oil change replace a oil of oil with Marvels mystery oil, the stuff really works. Change your oil in about a thousand miles. It is possible you have sludge build up on the lifters and they are not returning proporly and your have low compression. What oil do you use?