distributor cap and wire set (Yec), plugs new…accelerates well at 30 mph and up…at idle and slow speed and when I decelerate there are very quick, one second or less hiccups intermittent…about every 5 to 10 seconds…could it be fuel pump ? Or injectors .?..any help is surely welcomed with enthusiasm…mike
When this type of stuff starts to happen on a vehicle this old, the first thing I try is a can of SeaFoam motor treatment in the gas tank at the next fill-up.
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I had an '89 that had a carburetor, I believe the 90 is fuel injected. Just confirming.
Yes, the 4AFE is electronic fuel injected. That’s what the “FE” stands for.
I presume a new ignition rotor was installed w/the new cap. If not that’s the first thing to try.
Next check ignition timing and idle rpm and adjust if needed. And check the throttle position switch adjustment. Also read out any diagnostic codes from the ecm memory and address those. One of those confirms the throttle position switch is working correctly.
Still a no-go? Check for vacuum leaks. And that the air induction system remains intact w/no holes or leaks (the rubber boot from the air cleaner box to the throttle body).
Verify the engine is reaching the proper operating temperature too, if not, replace the thermostat. The 4AFE is very sensitive to engine coolant temperature being correct. If you’ve never replaced the thermostat in the life of this engine, it’s kaput.
If the hesitation problem persists, it’s likely some kind of fuel problem. Could be the fuel pump or fuel filter, but since it works fine at higher speeds, it is most likely partially clogged injectors. The fuel injection system must meter out a precise amount of fuel, and at low speeds where very little fuel is injected the degree of precision needed increases. If one or more of the injectors is slightly clogged, this can produce this symptom.
Do you notice this especially when going slowly, decelerating around a turn in neighborhood driving? If so, that would confirm a fuel injector problem. The first step then is as advised above, a fuel injector cleaning treatment. Some magic elixir into the gas tank. YOu may have to do this more than once. If it seems to work a little the first time, repeat.
Techron is often recommended here. When I had this problem, I used a product called “Clean Power” and simply followed the instructions on the bottle. Best of luck.
One thing to evaluate is if there’s play (up-down but especially side to side) in the distributor shaft. Does this engine need valve clearances to be adjusted? And is the ignition timing OK?
The 4afe does require valve clearance checks once in a while, but I doubt that’s the cause of this particular problem. My own 4afe has 200K miles and never needed a valve adjustment to date. But a worn distributor could indeed cause this, something definitely to check.
On an engine this age with these symptoms I’d do a compression test and put a vacuum gage on it. By doing so you’d be checking the internal health of the “bottom end” as well as checking for vacuum leaks and sticky, weak, and/or leaky valves. I’d want to know either of these before spending money on more easily replaceable components.
Yes, a flaky injector is a definite possibility, but I’d normally expect that to be more pronounced as you accelerate higher, when the need for a reliable fuel feed is more necessary. A fuel injector cleaner is worth the few bucks to try it, you might get lucky, but of it does not help that does not mean the injectors are okay. They’ve cycled millions of times and can wear out, AND they’re also subject to erosion just like the Grand Canyon.
Other possibilities are a flaky EGR valve. The EGR system is designed to allow a bit of inert exhaust gas to go to the induction system under conditions of high cylinder load, and if the valve isn’t closing properly it could be allowing exhaust gas in when it isn’t needed, interfering with the fuel/air ratio. Here’s some sketches that should help you figure out where to disconnect the EGR line (plug the lines when you disconnect it) to test for this.
There are countless other possibilities, such as a flaky igniter, a loose distributor shaft (check for “wiggle” side to side and excess axial play), a faulty crank position sensor (again, I would expect this to act up under higher rpms as well, but it’s a possibility), and some others, but between the existing posts you have a lot of work ahead of you already. Post the results. We do care.
Thank you everyone , specially George…The radiator fan has been coming on at the turn of the ignition key…which I was letting go (finding the switch)since we drive short distance in town,Honolulu seems to be normal now…start with injector cleaner, thermostat, move the distributor for play. wish my wife didn’t toss out my timing light 10 yrs ago. I have to hide my rags…she throws them in the trash. Will research Tps…oooo these Buick ads are driving me nuts…good to have football back…how’s the music Tester? I need a driver side visor …any ideas besides junk…oops, recycle yards…Tah…Mike
sunvisors can be found on ebay
But you have to consider if s/h charges negate a good deal
The radiator cooling fan turning on all the time could prevent the engine from reaching the proper operating temperature, which might cause or contribute to this symptom. Fixing the fan problem should be done before considering more complicated possibilities. It’s probably just the radiator cooling fan switch is stuck in the “on” position. It’s a gadget that screws into the cooling jacket and controls the radiator fan relay. It’s a common failure item. I’ve had to replace mine twice. You can replace the thermostat at the same time. Suggest not to delay, as if it can stick “on”, it can also stick “off”, and that could create an expensive engine overheating problem.
The only difficulty I’ve had with replacing that switch is obtaining the correct part. The parts stores seem unable to figure out which is which. There are 4 gadgets that screw into the coolant jacket in the same vicinity, one is the fan switch, one is a thermo-time switch which controls the cold start injector, one is the coolant temp sensor (for the ecm), and one is the coolant temp sending unit for the dashboard gauge. There’s another gadget in the same area that screws into the coolant path too, for the emissions canister operation, but that has no wires going to it, it is a vacuum switch only. The bottom line is to figure they parts store will be confused in your area too, so bring in the part with you and make sure what they give you looks like the same thing, with exactly the same connector on it. The sensor tip that pokes into the coolant path might look different, but the threads, pitch and diameter, and the electrical connector must be identical. & it’s a good idea to test the new part before installing it, by rigging up a way to heat it to 190 deg F or so, make sure it switches. I forget now if it is NO or NC. hmm … But I think they have it configured so if the connector accidentally comes off, the fan will spin, so it must be NC; i.e. the switch should register 0 ohms at temperatures below 190 deg F.