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Old 02-05-2011, 07:37 PM   #1
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Exclamation Help......

So here is what i know.....I just had the 2.5l in my '89 rebuilt (.03 over and a mild cam) and it idles smooth and when its up to temp i can put my foot to the floor and she gets up and runs but the problem lies in just trying to cruze down the road it starts to cough and sputter and if i dont change what im doing it will back fire....I got a new TPS today and couldn't get the output voltage up to the 4.6-4.7 that the book says it maxed out at 3.5...so ive got another one coming and that one got returned to autozone (after they put up a fight)... So my question is - is their any thing else i should be looking at as the culprate??? does the Ignition controll need to be remapped to compensate for the cam??


Ps. this is a great site with a wealth of knowledge

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Old 02-06-2011, 11:59 AM   #2
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Some one's got to have an idea...

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Old 02-06-2011, 12:03 PM   #3
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if u have a cam you need to upgrade ur INjectors and stuff since a cam requires more gas
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Old 02-06-2011, 12:13 PM   #4
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Check out your timing.....What RPM is the coughing/sputtering happening? I'm guessing you got the motor punched .30 over not .03 right?
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Old 02-06-2011, 12:16 PM   #5
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well usually if the timing is to advanced or wrong at low end it wouldnt accelerate good and high end it would make a ticking type noise. ur most likely not getting enough gas to handle the cam
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Old 02-06-2011, 12:22 PM   #6
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well usually if the timing is to advanced or wrong at low end it wouldnt accelerate good and high end it would make a ticking type noise. ur most likely not getting enough gas to handle the cam
Cam timing and ignition timing are 2 different things, you know this right? It may be within a running range but not correct possibly causing some of the issues the op is explaining.
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Old 02-06-2011, 12:25 PM   #7
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hmm i did not know this. I have a cam and those kinda goodies in my motor but i never knew i could adjust it
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Old 02-06-2011, 12:32 PM   #8
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hmm i did not know this. I have a cam and those kinda goodies in my motor but i never knew i could adjust it
What do you think a timing belt/chain does? It holds the timing betweeing the cam and crank. Have you ever torn into a motor? If someone were to put on the timing belt on with the cam a tooth or 2 advanced and then set the distributor according to that you are losing operational range.
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Old 02-06-2011, 12:35 PM   #9
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yup ive tuned my motor many different times and changed my distributer many diferent times (it is a jeep)
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Old 02-06-2011, 01:13 PM   #10
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I think the cam you put in is messing with the computer, the cam will change the lift and duration of the valves, thus changing the fuel and air mixture required, Usually in other applications the computer must be re-calibrated to compensate for this, even motorcycles now have to be re-calibrated when changing even the air cleaner/pipes..
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Old 02-06-2011, 01:39 PM   #11
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yup ive tuned my motor many different times and changed my distributer many diferent times (it is a jeep)
When dropping the distributor the cam timing is already set. It could be a computer/fuel issue but the idea of troubleshooting is to K.I.S.S.(KEEP IT SIMPLE, STUPID). Checking the timing with a light is really easy to do, much easier and cheaper than throwing new injectors or even a computer in. If the timing is good I would move onto the intake and exhaust, Do you have a stock intake? How about a header?
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Old 02-06-2011, 05:03 PM   #12
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Yes its a stock intake and the exhaust is unrestricted... I got a new tps but it topped out at 3.6v when the book says that I need 4.6-4.7v to be correct at w.o..... No I meant .03 not .3 (thirty thousandths 300 thousandths) ... I see most of the problems at 2k and up I'm even getting some sputtering at wife open now.... I've got a new fuel filter so its going in as soon as I'm done on this...
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Old 02-07-2011, 07:24 AM   #13
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Guys We are jumping in too deep and guessing way too much.The first place to start is with cap,rotor and wires ,coil,distributor.Read your plugs and that will tell you if it is fuel related.
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Old 02-07-2011, 09:22 AM   #14
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Check out your timing.....What RPM is the coughing/sputtering happening? I'm guessing you got the motor punched .30 over not .03 right?
You guessed wrong .030 is thirty thousanths over
.30 is 30 hudredths
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Old 02-07-2011, 06:03 PM   #15
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i've got new plugs, wires, cap and rotor and a new fuel filter.... my new tps is supposed to be here tomorrow...
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Old 02-07-2011, 06:22 PM   #16
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Okey I'm lost. I thought that '91 was first year for fuel injection.
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Old 02-07-2011, 08:27 PM   #17
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My 89 2.5l has TBI.
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Old 02-08-2011, 07:17 AM   #18
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The 2.5 got TBI sooner than the I6.Same on the S-10.The 2.5 had TBI two or three years before other engines.85 on S-10's and not sure on Jeeps.
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Old 02-08-2011, 11:36 AM   #19
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Okey I'm lost. I thought that '91 was first year for fuel injection.
Yes and they have a TPS..
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Old 02-08-2011, 09:07 PM   #20
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Okey, the '89 2.5 has tbi. If it has a o2 sensor and all the other sensors does the ecu store trouble codes?
Seams like the o2 sensor would compinsate for the larger cam.
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Old 02-08-2011, 09:43 PM   #21
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: dance:

thanks for all the help guys shes up and running now......

it was the TPS that was causing all my issues....

I talked to a Mech. and he said that the comp in the early YJ's is capable of handling the mild cam and larger bore of the new motor...So now its time to finish my bumpers and hit the hills...



here is a pic of my baby and my my buddies '68 CJ5 with the view of our home town in the back ground...
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Old 02-08-2011, 09:48 PM   #22
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I just found this random excerpt.........It fits this thread to a T

IMHO, you can pour money into a four popper to get more power but it will come in at a very high rpm. Not useable on the trail and marginally useable on the street. You want to scream it at 4 or 5 grand just to pull away from a stop sign normally? There is no replacement for cubic inches. Please don't let me put you down for wanting to do this, a Jeep is a Jeep is a Jeep in my book. I just have seen people spend alot of money and get little return from a 4 banger. The trap with a 4 cylinder is: I'll put a bigger cam in it, It still isn't enough. Then someone says well with the bigger cam the engine needs to flow better, now you get a header, not enough. For the front end a new intake and too big carb, still not enough. It will keep going and going, not enough. Calculate how much money you would spend(forget blood sweat and tears) and compare this to swapping in a healthy six or eight, a baseline that will give you enough
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Old 02-08-2011, 11:00 PM   #23
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I just found this random excerpt.........It fits this thread to a T

IMHO, you can pour money into a four popper to get more power but it will come in at a very high rpm. Not useable on the trail and marginally useable on the street. You want to scream it at 4 or 5 grand just to pull away from a stop sign normally? There is no replacement for cubic inches. Please don't let me put you down for wanting to do this, a Jeep is a Jeep is a Jeep in my book. I just have seen people spend alot of money and get little return from a 4 banger. The trap with a 4 cylinder is: I'll put a bigger cam in it, It still isn't enough. Then someone says well with the bigger cam the engine needs to flow better, now you get a header, not enough. For the front end a new intake and too big carb, still not enough. It will keep going and going, not enough. Calculate how much money you would spend(forget blood sweat and tears) and compare this to swapping in a healthy six or eight, a baseline that will give you enough

that is abosolutely correct...."their is no replacement for displacement"
ive had v-8 trail rigs but i just love this little 4 banger in this jeep.... i keeps my outta trouble and has been loyal from day one...now if she wasnt my daily driver and money wasn't an issue then i would have swapped a stroked I-6 and called it quits....but i got this motor rebuilt and all new incidentals (fluids, hoses, wires, ect.) and the new TPS for less than 2K ... i now have a brand spanking new jeep from the radiator back (trany/ t-case and front and rear ends have been gone through) that should last me till im tired of it....

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