'94 Ranger, 4 cyl, 2.3 L, 348k miles....vibrates/shakes for the 1st 3-5 minutes after I start it up from a cold start. Runs fine after that. Doesn't die, RPMs are steady, no "check engine" light; it just shakes. Once it warms up it's fine. What gives?

 

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A few questions: is it automatic or stick?

While it's warming up and doing the shaking thing, is it running normally or is it rough, like maybe it's not hitting on all 4?

Is this something that's just started recently, or has it been doing it for a while? Looks like you've got a few miles on it!

 

Hi,

It's manual transmission, it runs rough while warming up (although I just don't think it is missing because it goes away once it warms up, also has new Motorcraft spark plugs and wires), it has been doing this for about 1 yr, it does it 8 out of 10 cold start ups. As you can tell it is difficult to "show" the problem to a mechanic since it only happens when it has sat for hours and only lasts 3-5 minutes. Any clues would help.

Also, I'm a delivery driver in Dallas; hence, the high mileage....



Thanks for the help, Mike

 

Is there any difference when you push the clutch in? Does it just do it while idling, or does it do it if you rev the engine up or put it under a load (like driving)?

It does sound like a cold miss, but I'm thinking it's from dirty injectors rather than ignition. I would run some fuel injector cleaner through it, and try cleaning the throttle body and the MAF to see if that helps.

 

Check for condensation on the spark plug insulators. You replaced the plug wires, and state the rpms are steady. I'd bet the rpms are not steady, but the signal the tach looks at is steady. You may have bad wires from the factory, as you don't state if the problem came up after swapping the wires. I added a problem once by replacing a coil that I thought was on its way out with a new one. What a pain chasing a problem caused by new parts.
tom

 

No difference if the clutch is pushed in. It runs rough for those initial 3-5 mins whether it idles, rev it up, or drive it. I tend to agree with you as far as the dirty injectors, can you recommend a cleaner? I use an STP cleaner after every oil change, but maybe it needs something stronger after 340K+ miles. Also, I'll check the throttle body and MAF. THX.

I've replaced the wires and plugs twice since this problem began. Both have checked out fine both times. No condensation, no sludge, nothing. As far as the rpms, why would the signal that the tach looks at change once the engine warms up? The truck has passed its inspection twice since this problem began, during which the rpms are checked. I'm just not sure its the rpms, or maybe I misunderstood your train of thought. Thanks for the help, keep it coming.

Hey Dan, I forgot to ask, if it is a fuel injector problem, why does the engine even out once it warms up? What happens to the injectors after those 1st 3-5 mins? Do they actually warm up or what? thx

 

A cold engine can amplify some symptoms. I would think you'd still be grtting some symptoms after the truck is warm, just not as noticable.

Have you had the codes pulled? That's really where we should have started. That would show us if the problem is in the IAC, or possibly the EGR if the injectors turn out to not be the culprit.

Here's another possibilty, strange as it sounds: Check the fan for cracks or breaks that could throw it out of balance. Those plastic fans are notorious for cracking. The fact that it causes a problem only when cold would be related to the fan clutch.

 

The tach looks at the signal that is used to fire the coil. It does not know if the engine actually fired, just that the signal is present. Eventually, the tach will show the rpm drop, if it is significant enough to lower the firing rate, but will not show intermittent glitches as it cannot respond that quickly.
Again, pull the codes. Check the ACT and ECT sensors for incoming air temp and coolant temp readings. If one or the other is bad, the ECM will not increase the fuel flow while the engine is cold, much like the choke does on a carburetor. It will leave the injector at the leaner setting it uses for warmed up engines, leading to a cold temp miss, and rough running.
tom

 

Sorry for taking so long guys. You mentioned pulling the codes, but the check engine light never comes on, therefore there are no codes.....right? or is there another way? thanks for the help, you guys have given me plenty of leads to go on, I'll start checking sensors (ACT, ECT, IAC, EGR). THANKS AGAIN.

 

There are many codes that can be stored without triggering the CEL, so you should still pull them and have a look.