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Old 09-21-2010, 10:21 PM   #1
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98 tj 4.6 stroker pinging

I just installed a 4.6l stroker in my brothers jeep. All of the info I see out there says the computer will adjust. I knew better than that it is a speed density program it doesn't know it is 16% larger engine. Needless to say the engine pings and is needing 20% more fuel according to the fuel adaptation on the scan tool. I have larger injectors ordered. I would like to know does anybody know of any companies that would program a computer for this specific motor.

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Old 09-21-2010, 11:13 PM   #2
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there's a company in northern illinois near rockford called "Irish's Offroad" that claims to do all needed work to upgrade to the 4.6L. I know nothing about them or even if they're legit (craigslist) but the ad looks like they know what they're talking about. their #
815 355 1652
let me know if they are legit; i was tempted....

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Old 09-22-2010, 08:19 AM   #3
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Thanks for the info I will call today and post my findings
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Old 09-22-2010, 09:09 AM   #4
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no problem... here is the original craigslist ad I found:

http://chicago.craigslist.org/nwc/pts/1954641177.html
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Old 09-22-2010, 11:31 AM   #5
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Called Irish Offroad this morning waited several hours have not heard anything from them.
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Old 09-22-2010, 11:32 AM   #6
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24# injectors out of a Big Block Ford should work for you
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Old 09-22-2010, 12:31 PM   #7
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Sounds stupid but what octane gas are you running?
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Old 09-22-2010, 01:38 PM   #8
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I have not been able to find anything concrete on stock injector size, But what I have found they came stock with 24# injectors. If you multiply 24 * 1.20 (add 20% to the injector size) you come up with 28.8. If You use the formula (expected hp * .5) / (# of cylinders *.8) I came up with correct me if you think i am wrong (260 * .5) / (6 * .8) = (130) / (4.8) = 27.0833. So what it comes down to is I ordered 28 # injectors. The octane of fuel I am running 91 is the best we can get here with out going to $7.00 gallon race fuel. I am open to any suggestion even if they are way out in left field. Maybe i missed something.
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Old 09-22-2010, 01:40 PM   #9
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I don't think they came 24's stock man...what color are they? Most I have seen are either grey or yellow.
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Old 09-22-2010, 01:51 PM   #10
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I believe they are grey.
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Old 09-22-2010, 01:57 PM   #11
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with the kit you bought, was there mention of the compression ratio?

newer naturally aspirated 5.0/4.6 cobras came with 24# injectors. they are light blue and a very common upgrade for h/c/i 5.0 cars, so i'm sure you can find a set for cheap. 30# are red or green and are also pretty common.
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Old 09-22-2010, 02:11 PM   #12
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Greys should be 15#....the only stock 24# ones I have seen are in 1st gen lightnings and 460's.
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Old 09-22-2010, 02:16 PM   #13
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Just got off the phone with the guy from Irish Offroad. He tells me he doesn't think the computer needs to be flashed. He gave me some info on timing that I was unaware of. I am going to restab the distributor and I will post more after I do that. If anybody can give me definite on what # injector was in a stock in a 98 4.0l wrangler engine i would greatly appreciate it.
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Old 09-22-2010, 02:17 PM   #14
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cobras have them, trust me.
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Old 09-22-2010, 02:18 PM   #15
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Thanks for the numbers it is a big help. I will post again after I restab the distributor.
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Old 09-22-2010, 03:31 PM   #16
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Yeah they do, didn't see "cobra" in your post. But he is way more likely to find a set out of a 460 in a pick and pull yard.
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Old 09-22-2010, 07:58 PM   #17
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well what i mean is they're all over on the net since so many guys either go bigger or upgrade the base 5.0 from 19# to 24#
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Old 09-22-2010, 08:51 PM   #18
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Yeah I hear ya....but if he has access to a pick n pull yard they can be had for 15 bux for a set
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Old 09-22-2010, 09:08 PM   #19
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Do a compression test. That could tell ya alot
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Old 09-22-2010, 10:29 PM   #20
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I rather doubt bigger injectors will do anything - except maybe at WOT and high R's.

The computer will just shorten the open time on a bigger injector, cutting back the fuel to maintain the correct air to fuel ratio. Picture a coke bottle - it can only hold so much water no matter how big the filler hose is.

The way it works - the O2 sensor senses the Oxygen content in the exhaust, the computer "reads" it, determines if it's too rich or too lean, then adjusts injector open time to get the correct A/F ratio. The correct A/F ratio has nothing to do with displacement. All engines, from the tiniest to the biggest are most efficient when the air to fuel ratio is correct.
In the old days (carbs) we used to richen it super rich to stop the pinging - we weren't addressing the real problem, but it stopped the ping. We were simply flooding it with the cooling effect of lots of fuel. Water worked too.

I really doubt it's a lack of fuel.

Timing is controlled by the computer, it is pre-determined the correct timing - again, timing has nothing to do with displacement. Notice the timing curve for a 454 is about the same curve as a 4.0.

But - the plugs you used - are they the stock ones? If you are using so called "trick" plugs try stock plugs. No splits, duals, triples, rings, yellows, blues, red etc. Plain old cheapie stock ones the factory used - I prefer Champs, but others will work well too - except Bosch! (They use "one size fits all" - ask your wife how "one size fits all" fits her.)

When you stroked it, did you also shave the head or modify the combustion chamber - like change the shape of it? If you took that step, then surely you CC'd it too.

What I'm thinking is hot spots in the combustion chamber causing the pre-ignition (likely the plugs). If you relieved the combustion chamber by grinding, the plug shell may be hanging down too far - glowing.
Using non-standard "trick" plugs is another problem. Just because it "fits the hole" doesn't mean it dissipates the right amount of heat throughout the entire RPM range.

And - another thought - there are several head gasket configurations for 4.0's around - many will plug off the water jackets in such a way the head runs too hot, or makes hot spots. I found out the hard way fitting an 00 head to a 90 4.0.
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Old 09-23-2010, 12:12 AM   #21
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This motor is not a kit. It was built by the machinist here in my home town. Who is responsible for a good portion of the hot rod motors you see in the boats on the southern colorado river and at the sand dunes just over the border in california. The compression ratio is close to 10 to 1 I know that. I also know that the computer is adding 20% more fuel. I am not saying the toiming is the problem I am saying the problem is a combination between the amount of fuel and the amount of timing at any giving time. The computer maps this out so to speak. This engine does not have a stock cam. So the amount of vacuum it creates at any givin time compared to throttle position and RPM,s is different than a 4.0l. With this being said the computer does not know it does not have a 4.0l at the end of its wires so it is doing what it thinks the 4.0l needs. At any givin time is probably a little bit different than the high compression mild cam 4.6l.
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Old 09-23-2010, 06:51 AM   #22
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I would still check cyd pressure. higher compresson and a cam not ground right. can make you pull out your hair.
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Old 09-23-2010, 09:35 AM   #23
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I am with rrich and tailhole on this one. You need to find what your DCR is. I have seen people mention that any higher than 8.5 DCR, you will need race fuel. Also, it depends on where you live like altitude, air density etc.

Another thing that helps reduce pinging is good quench. 0.040 to 0.050 is very good. Do you happen to know yours?

If your DCR and quench are okay then what rrich recommended will apply to you.
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Old 09-23-2010, 09:44 AM   #24
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8.5 and race fuel? I run a 10.5 460 on the street with 87 octane with no issues
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Old 09-23-2010, 10:49 AM   #25
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The computer doesn't care what the displacement is - all it wants is to keep the A/F ratio in line.
Notice there is not any input or programming for the computer to know what the displacement is.

The computer's ultimate and most influential sensor is the O2 sensor. It tells the ECM WHERE it is as far as A/F ratio. All the other sensors inputs, like TPS, MAP etc are only inputs to help the ECM "predict" the needed A/F ratio to prevent stumbling, sag etc. Remember the O2 reads it "after", - it reads the results. Without the other inputs it will sag.

You didn't answer about plugs you are using.

The new cam - your engine builder should know this - the intake manifold vacuum always pulsates (you don't see it on a regular vacuum gauge, the gauge is dampened and the pulses are very fast. You need a vacuum transducer to see it. In stock form that pulsation is fairly minor. The MAP sensor reads that vacuum and is designed to smooth or "average out" the pulsations to get what it needs. But it can only do so much.

When you change the cam you are treading on thin ice. You can increase valve lift a little without increasing those pulsations by much, but if you change duration or overlap by much, the pulsations radically increase. (Look at the "big" cammed (rumpity rump) race engines trying to idle with a carb - they drive the carb's circuits crazy - but they don't care about idle, only WOT.)

Those pulsations drive the MAP sensor nuts! Those pulsations may be cutting the fuel down to the point it's running lean and pinging. The MAP "averages" the readings, where a carb switches between circuits - idle, tranfer, main, then back to idle. The reactions between carbs and MAPs are different, yet still upsetting.

Try 4 things -
1. Try artificially enrichening the mixture with propane. Get a cheapie propane torch - remove the tiny restriction orifice - or drill it out - remove the torch tip and slip a long hose over the tube. Screw it on a small propane canister.
Tape or attach the end of the hose in the intake airstream, take the bottle with the valve in the cab with you.
Run it up to speed, make it ping - then holding the bottle valve down, add some propane. If it is running lean the R's will increase (it likes it) and the ping will stop.

If the mixture is correct, adding a small amount of propane (fuel) will not change the R's. Adding more will cause the R's to drop. That means the A/F ratio is already correct.
If adding the R's go way up, then it was too lean.
But - remember the ECM monitors the O2 - so whatever you do will only be temporary for 2 or 3 seconds, then the ECM compensates for your enrichment.

Way too rich should stop the ping - by the cooling effect of being too rich, but performance and mileage will suffer.


2. Remote mount the MAP Sensor (get creative) - use a very long and large hose for the vacuum - the long large hose will dampen the pulsations - or use some kind of canister - like a fuel filter to act as a dampener. See if that helps.

3. But still - the plugs - you should by now be able to see if they are creating "hot spots." Try stock plugs or even 1 or 2 clicks colder.

4. Use an infra-red thermometer from underneath - see if one exhaust temp is way hotter than the rest, indicating cooling troubles - head gasket etc. Try it right after you run it at 2500 for at least 2 minutes.


Larger injectors - there were enterprising 2 guys that took their truck to the market to buy watermelons. They paid $.50 a pound for them.
They found a street corner and set up to sell them. They sold them all for $.50 a pound, they sold them all by noon.

One said to the other - why didn't we make a profit, we sold them all?
The other said "because we ran out of them too fast, we need a bigger truck!"

Bigger injectors?

Let us know.
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Old 09-23-2010, 12:40 PM   #26
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Ive seen it to many times. you get a cam say 218-224 on 114 and think its what it says it is. But when checked 224-224 on 108. and end up 220 cyd pressure. Also was the cam degree?
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Old 09-27-2010, 10:38 AM   #27
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Quote:
Originally Posted by Ibuildembig
8.5 and race fuel? I run a 10.5 460 on the street with 87 octane with no issues
10.5 must be SCR not DCR.
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Old 09-27-2010, 10:54 AM   #28
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Static ratio, yes

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