JeepCop44 Posted February 8, 2017 Share Posted February 8, 2017 Been trying to track down the cause of this on my '88 Pioneer 4.0, 5 speed. There's a random popping in the intake while idling, and will make a nice loud pop when hitting the throttle. I replaced the vacuum harness and changed spark plugs and wires. I'm going to check the timing next, probably should check the fuel pressure, going to seafoam everything, make sure the Distributor is clean and not warped, make sure the wires are hooked in the right sequence, then start cleaning/replacing sensors. I've been just doing research trying to narrow down what can cause this. if none of these work, at least I'll have cleaned up some stuff in the engine bay. If anybody has any other suggestions I'm all ears and will give any advice a shot. You can here some more engine noise in the video, I'll be trying to find the cause of that too. Also.. there's a connection coming off the harness around the intake and vacuum lines that is not connected, and I havn't been able to find a place to plug it in for the life of me. I'm thinking it has to be a sensor that just is on automatic transmissions, mines a 5 speed Link to comment Share on other sites More sharing options...
SVPete Posted February 8, 2017 Share Posted February 8, 2017 That doesn't sound like backfiring to me. Your engine noise reminds me of a street sweeper engine that had a push rod slip out of place on a valve rocker arm. You may be able to peek at some via the oil fill hole on top of the valve cover. If the connector you are referring to is a four wire plug near the throttle position sensor, yes, that is for automatic transmissions. Link to comment Share on other sites More sharing options...
omega_rugal Posted February 10, 2017 Share Posted February 10, 2017 a valve is not closing properly... Link to comment Share on other sites More sharing options...
Marine1Texas Posted February 10, 2017 Share Posted February 10, 2017 sounds like a intake valve is not closing all the way and compression is pushing past valve to the intake. you either have a sticking valve or a bent one. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 10, 2017 Share Posted February 10, 2017 Rent / borrow the pressure gauge from AZ or similar chain and do a compression test on all the cylinders. Link to comment Share on other sites More sharing options...
JeepCop44 Posted February 11, 2017 Author Share Posted February 11, 2017 Thanks guys! I'll let you know if I figure it out. Link to comment Share on other sites More sharing options...
JeepCop44 Posted February 12, 2017 Author Share Posted February 12, 2017 Pulled the valve cover off today, and you can see in this video that the rocker closest to the front of the engine is completely still. You see me push on the back side onto the rod, and when I do that it starts jumping. When it wasn't running, I could wiggle the rocker all around, there was no tension on it. and I could compress the rod down when I applied pressure. I pulled the rod out and it looks to be straight. Here's the video Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 12, 2017 Share Posted February 12, 2017 Quite possibly a collapsed lifter. Link to comment Share on other sites More sharing options...
JeepCop44 Posted February 12, 2017 Author Share Posted February 12, 2017 That's what I've been leaning towards... could it be a rounded off cam lobe? Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 12, 2017 Share Posted February 12, 2017 That too. But usually it's more than one lobe when a cam goes....... Link to comment Share on other sites More sharing options...
Hippie66 Posted February 14, 2017 Share Posted February 14, 2017 Either the nut backed off, or collapsed lifter. Link to comment Share on other sites More sharing options...
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