Hi everyone. I haven’t posted in awhile but it’s good to be back. I’m in the middle of a tune up on my 89’ 4.9 4spd. What I’ve done so far,
oil change, fuel filter replaced,
plugs, plug wires, cap and distributor looked new so I left it. New coil, map sensor, tps sensor, idle air control sensor, Pcv valve, Removed air pump and egr tube and capped both ends Left the egr plugged in, New vac lines for what was left with a new coffee can. Cut out both cats right after the o2 sensor and went 2 into 1 super 40 flow master. New steering box drag links and tie rod ends. 2” sky jacket lift leveling kit.
What’s left, exhuast manifold leaking... so will be pulling it and adding a remflex

gasket and checking manifolds for cracks. The truck only has 2 issues right now, it’s starts great but after it drops down to about 1k it fluctuates back and forth from about 800 to 1200 but stops after it warms up. Also bucks in reverse. I’ve tested fuel pressure with Guage and get about 10psi with just key on engine off. Engine on running it sits at 48ishpsi. 55psi with vac line pulled off fuel pressure regulator. Also sprayed carb clean all around intake for leaks no spike in rpm. It does the same fluctuation after driving for a bit parking then restarting. Almost to the point of stalling but eventually goes away. Most likely will pull all injectors and test them. No check engine lights and flys down the highway no prob. Any thoughts on the reverse bucking and start up surge would help. Also would like to know what the heck this thing is on my fuel rail.

Thanks.

 

That's not a tune-up; it's a butchering.

The device in the pic is the temperature switch for the injector blower. Click this & read the caption:

(phone app link)

 

Thanks for the input. Truck runs way better with everything I’ve done. Just cleaning the engine bay up to be able to access stuff easier and replacing sensors in hopes to cure the fluctuation. Throttle stop is adjusted to spec in my manual. Distributor moves freely with no slop. Battery terminals are clean with electric grease and tight. Routed my existing new vac lines using vac diagram in manual and diagram sticker ontop of air box. Also timed with timing light to spec. Will look at at ecm and check the board. The truck was kept in great shape form previous owner. Zero rust. Interior like new. Truck has had the fluctuation and reverse bucking since I purchased it.

 

I would swap back the air cleaners...sometimes these units are too small air flow for what the engine needs.

In the future, I would suggest doing one repair/upgrade/fix at a time and make sure you still have a correctly running rig. When you swap out that much, troubleshooting gets tougher. It is really easy to miss something as simple as a plug wire or vacuum line location.

Just my experience.

 

Those filters are about the same size as the cone filter for a cold air intake. The sensors replaced were not all done at once. Removal of the air pump, running a smaller belt and removal of the airbox makes it really easy to get in and around the engine bay. Truck drives fabulous down the highway and really pulls hard when shifting. Each sensor I tried was to try to fix the fluctuations that existed and still exists from when I bought the vehicle without any of this being done.

 

Well... think I found my issue

caps in the ecm done leaked on me pretty bad... Anyone know which emissions ecm I need to run ? I know it’s not the California one.

 

That's impressive - I've never seen one where the printed circuits have delaminated from the board. There are places that you can send it to be rebuilt, which is what I'd recommend. But I've never sent one off, so I don't have one specifically to recommend.

I believe you can run any 4.9L EEC from '87-93. If you get one from a truck with an E4OD, it'll set codes for the missing transmission, but those codes don't turn on the CEL.

 

is that your spout connector unplugged in the air filter pic?

leaving the egr functioning lets you run more advanced timing, which results in more power and economy.

 

The egr is still connected the pipe is just removed and capped at both ends so the ecm still thinks it’s there I’m just not recirculating exhuast back into my intake. I know it’s done mainly for emissions. But to me, exhaust back through my intake means carbon buildup on many components which can gum stuff up. Spout connector near the distributor has the plug in it.

 

sure that doesnt set a light..but the egr actually functioning is what im describing. you seem to want to try making more power, and with a basically stock 4.9, the egr encourages it. the 4.9 isnt far from pinging when everything is working perfectly, but does like the timing bumped a bit. the egr helps with running more timing, and decreasing emissions at the same time.

have never had problems with any components gumming up on egr equipped vehicles, that run well in the first place.