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Rev limiter

jd4242

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What would cause my rev limiter to kick in early and at random rpms?? (On my 94 ranger 4.0 5speed )

It kicks in at random rpms...like 3800,4000,4200 and back to 3800..then sometimes it goes to stock 5200..completely random. .

No codes..im thinking bad crank sensor or coil pack..had other problems with this coil pack and wires dropping a cylinder when it gets wet when it was in my big truck..
 
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2stroke

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I don't have a real answer for you, as I've never heard of this happening. Every 4.0 I've seen had a 4800 rpm limiter. Does it just stop revving or does it cut out for a second? I wouldn't worry too much if it's the only problem, the motor quits making power after 4 grand.
 
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jd4242

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I don't have a real answer for you, as I've never heard of this happening. Every 4.0 I've seen had a 4800 rpm limiter. Does it just stop revving or does it cut out for a second? I wouldn't worry too much if it's the only problem, the motor quits making power after 4 grand.

My rev definitely is set to 5200.it cuts in and out just like it would if you hit the limit on a stock motor..

And ooo im definitely worried about it as my motor definitely doesnt stop making power at 4 grand,its nowhere near stock..but this issue would or could happen to a stock motor..i wouldn't suggest you go bouncing of the limiter multiple times in a stock motor but for mine its not hurtn much.when i had my tune on this motor my rev limiter was set at 6200

Something is reading rpms wrong.only things i can think of is crank sensor,tps, coil or IDIS module. .

It seems to kick in even lower when pedal is FULL wot but still does it no matter pedal position. .last night it kicked in at 2800 in first ,3000 in 2nd and 5000 in 3rd..
 
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2000StreetRod

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Crankshaft position sensor?

Assuming your engine is fairly stock and the AFR is normal then I would suspect the crankshaft position (CKP) sensor or the ignition module. Try cleaning your CKP sensor by disconnecting and reconnecting it a couple times. Also check the connector to the ignition module.
 
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natenkiki2004

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Being a 1992, you only have a crankshaft position sensor, it's entirely responsible for the computer knowing how fast the engine is turning. If it's faulty, your timing would be screwed up and I'd imagine you'd have warm-start issues as well. I doubt it's the crank sensor since you only mention a rev limit as the problem. Aside from that, I don't have any suggestions for you.
 
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2000StreetRod

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94 Ranger

On a 94 Ranger the CKP sensor connects to the ignition control module.
Ranger94Ign.jpg

The ignition coil is another good possibility. Also, you might try disconnecting the radio noise capacitor. Sometimes they will fail in an erratic short mode.
 
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Ive had weak fuel pumps do it on my old bronco with a 351. Or may be a fuel filter clogging/colapsing. Check the pressure and volume.
 
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jd4242

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Think ill start by replacing the cps and coil..i have spare ones..

Doubt its a fuel pump..pump,filter and lines are all brand new and have plenty of psi
 
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jd4242

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Well replaced my coil and wires.no change..i did however find a bad plug wire or i broke it..gonna do crank sensor next.
20150926_171941_zpswinnudcg.jpg
 
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jd4242

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Its definitely happening at WOT way worse and earlier. .i can play with the pedal and it will ""almost"" not do it,least it will take it up past 4500 close to 5000
 
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jd4242

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Check the connector to your TPS and test the TPS for voltage dropouts.

I actually did this just last week,it checked fine..ill check again to make sure i didnt damage it though
 
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jd4242

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Fixed it and man what a difference.it was the crank sensor.. .truck is way faster when you can take it up higher and enter next gear at higher rpms..idles better and the A/F seems to be more steady..

Here's a crappy video of before.its kicking in around 4k in 3rd gear..
https://youtu.be/_LzXQ7eVG-Y

And here is it going up to 5200.i was getting on the highway both videos and shifted to 3rd early so i could make sure it had plenty of time at FULL WOT..dont think my camera or i could film first or second gear,goes way to fast..
https://youtu.be/QYoqkO0R8Ks

^^its actually doesnt kick in,i let off gas at 5200 when my shift light came on.
 
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malohnes

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Great job fixing your truck, JD!
 
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jd4242

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Great job fixing your truck, JD!

Lol thanks..it literally was driving me crazy and i have never seen another thread with same issues but then again i dont think many take it up that high and bounce it off like i do..:dunno::crazy::crazy::burnout::burnout:
 
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natenkiki2004

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Very interesting. I would have bet money against the crank sensor. Maybe it just couldn't handle/count/see the engine spinning faster than 4k?
 
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malohnes

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Very interesting. I would have bet money against the crank sensor. Maybe it just couldn't handle/count/see the engine spinning faster than 4k?

I did not think it was the crank sensor either. I was leaning to the ICM. IT just goes to show that sometimes the simplest solution is often the correct one.
 
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jd4242

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Guess i got lucky..lol but definitely fixed it.also just a fyi i took it off my spare motor,its a stock unit..

Side note..i was looking for the EDIS and couldnt find it..i found the ICM on drivers side behind headlight..on my explorer the EDIS was behind passenger headlight. .does this 94 ranger not have a EDIS,?
 
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natenkiki2004

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I think the ICM is the EDIS. Ignition Control Module vs Electronic Distributorless Ignition System. The "system" in EDIS is the ICM.
 
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jd4242

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I think the ICM is the EDIS. Ignition Control Module vs Electronic Distributorless Ignition System. The "system" in EDIS is the ICM.

I swore my 92 ex had both..been a min tho..the 92 definitely has a much different module that clearly says EDIS on it..that i do remember
 
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