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Old 11-19-2013, 04:07 PM   #1
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88 yj stroker failed smog

I took my jeep to get it smogged and it failed NOX at 25 mph, seems to run a little lean . Its a 4.6l stroker Im running 24 lbs injectors ,the head is ported the chambers are polished im running a crane cam (not very big just cant remember the specs on it right now) , ported zj intake manifold and bored out throttle body, stock exhaust manifold with 2.5 inch exhaust and cat. wondering if anybody running a similar set up , I need to step up on the injectors but dont know what size to go to . jeep runs good by the way very responsive good power

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Old 11-19-2013, 04:22 PM   #2
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Being an 88 it isnt consider historic or something where it is exempt to that test?

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Old 11-19-2013, 05:18 PM   #3
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Originally Posted by Wranglin4Life View Post
Being an 88 it isnt consider historic or something where it is exempt to that test?
Most states 20 years is considered historic unfortunately the state I live in does not follow that.
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Old 11-19-2013, 05:37 PM   #4
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I live in CALIFORNIA, THE WORST STATE FOR SMOG LAWS
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Old 11-19-2013, 05:47 PM   #5
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Wow that really does suck. Here in Ohio we have no smog check where I live.
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Old 11-19-2013, 06:07 PM   #6
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My problem is always the visual inspection lol. When I had a 4.7l stroker in my old xj, I used accel 26lb/hr injectors, 24lb/hr injectors seem small.
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Old 11-19-2013, 06:38 PM   #7
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You did NOT hear this from ME but try dropping 1 Quart of Denatured Alcohol, better known in the Drag World as METHANOL in a nearly full gas tank, mix it by topping off, take it for a nice long drive to warm it up, drive to the smog station and DO NOT shut it off unless asked by station personnel. Mine finally passed once I tried this and AZ is about as restrictive as CA on smog, but not quite thankfully..!
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Old 11-19-2013, 07:02 PM   #8
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Thanks, I will try that alcohol mixture , but also think I need to upgrade to the 26 lbs injectors just to be on the safe side I don't want to burn a valve or a piston also I'm going to hook up a wideband o2 to see where I'm at on the mixture
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Old 11-19-2013, 07:22 PM   #9
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Adding larger injectors will not help. In the simplest terms the ECM reads the O2 sensor and adjusts the injector pulse width to maintain 14.7 AFR. The only time larger injectors are useful is when the ECM is in open loop. Same goes for fuel pressure.

If you suspect a mid range lean condition then about all you can do is add on one of the aftermarket "black boxes" that modifies the O2 signal to the ECM.
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Old 11-19-2013, 08:34 PM   #10
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Adding larger injectors will not help. In the simplest terms the ECM reads the O2 sensor and adjusts the injector pulse width to maintain 14.7 AFR. The only time larger injectors are useful is when the ECM is in open loop. Same goes for fuel pressure.

If you suspect a mid range lean condition then about all you can do is add on one of the aftermarket "black boxes" that modifies the O2 signal to the ECM.
Actually with OBD1 vehicles, adding bigger injectors does make a difference. If the computer can't add enough fuel because the injector is too small, it will be a problem. I went through this with my 93 cherokee that I stroked.
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Old 11-19-2013, 08:46 PM   #11
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Actually with OBD1 vehicles, adding bigger injectors does make a difference. If the computer can't add enough fuel because the injector is too small, it will be a problem. I went through this with my 93 cherokee that I stroked.
That is true but by the specs of his build I highly doubt that he needs anything above 24 lbs. Perhaps a little more fuel pressure but without a wide band O2 sensor monitoring the AFR it can only be a guess.

On your Cherokee you were liking exceeding the injector duty cycle (approx. 80%) max and covered up the problem with larger injectors. When most likely it could have been fixed differently.

You can dump 30 lb injectors and the ECM will adjust the AFR to 14.7 in closed loop.
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Old 11-20-2013, 01:26 AM   #12
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Since you are stroked, you are kinda screwed, but your motor is still susceptible to normal common BS:

Make sure there are NO exhaust leaks before the converter.
Make sure your O2 is working correctly.

You are running MORE Cubic Inches (Volume) then the stock computer is used to, do you have a custom calibrated computer?

You have all this fancy porting and polishing to get the air INTO the motor, but nothign to get it out, try a set of headers, there is a smog legal version for the 4.0L, check for one for the 4.2L (or did you swap in a 4.0L? Kinda sounds like it with the PFI setup you describe).

Oh, and guys, in Cali you smog EVERYTHING 1976 and newer. EXCEPT Hybrids. Diesels 1997 and older (also diesels over 14500 GVWR) are exempt.

Quote:
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If you suspect a mid range lean condition then about all you can do is add on one of the aftermarket "black boxes" that modifies the O2 signal to the ECM.
There is also the trick to put a BB in the FPR vacuum line, which works great until WOT, then its normal.
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Old 11-20-2013, 07:59 AM   #13
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Quote:
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Since you are stroked, you are kinda screwed, but your motor is still susceptible to normal common BS:

Make sure there are NO exhaust leaks before the converter.
Make sure your O2 is working correctly.

You are running MORE Cubic Inches (Volume) then the stock computer is used to, do you have a custom calibrated computer?

You have all this fancy porting and polishing to get the air INTO the motor, but nothign to get it out, try a set of headers, there is a smog legal version for the 4.0L, check for one for the 4.2L (or did you swap in a 4.0L? Kinda sounds like it with the PFI setup you describe).

Oh, and guys, in Cali you smog EVERYTHING 1976 and newer. EXCEPT Hybrids. Diesels 1997 and older (also diesels over 14500 GVWR) are exempt.



There is also the trick to put a BB in the FPR vacuum line, which works great until WOT, then its normal.
Wow what a response. OBD1 ECM`s are not reprogrammable.....I am working with a couple people to be able to actually change the Eprom so in the not to distant future that might change.....so that is a pointless question. Properly set up there is no reason why a OBD1 controlled stroker cannot run well and efficiently.

Putting a BB in the FPR vac line will cause a lean condition skyrocketing the NOX level.
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Old 11-20-2013, 08:14 AM   #14
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I'm running a 4.0l block with the original 4.2l crank 4.0l pistons bored over .030 the ECM is a Mopar unit that came with the EFI conversion it has timing adjustment capability with the DRB 2 the advance is adjusted all the way down 6 degrees below the stock setting the the idle is good , once it's starts going , the CO reading goes to .04 at 15 mph and zero at 25 mph it leans . . I personally don't think the stock HO header flows to bad from idle to around 4500 rpm an aftermarket header wouldn't benefit too much the cost vs power isn't worth it in my opinion
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Old 11-20-2013, 08:56 AM   #15
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That sounds a lot like the Hesco FI system.

Any idea what your quench is ? Do you know if the cam was installed straight up or advanced ?

Using the DRB1 I would crank a few degrees of timing into it unless your already pinging. If so then a mid grade or even a premium grade fuel and a few degrees of timing will lower your numbers. Right now your lack of timing is raising the NOX levels.

I run .043 quench with a lot more cam then your running. Advanced 4* and timing set 6 degrees above the factory setting by modifying the crank sensor. Plus the IAT is in the CAI rather then the intake manifold. The 63mm TB has a additional bleed hole in the throttle plate which helps with idle and coast down. 43 lbs of FP with the vac line connected.
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Old 11-20-2013, 09:59 AM   #16
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I'm going to install an adjustable pressure regulator in the return line withe the o ring removed from the regulator in the rail and I'm installing a wide band that I'm borrowing from one of my other projects just to see what it does with increased fuel pressure , I don't have any pinging problems I usually run 89 octane but I filled the tank with premium for the smog test . Also I will bump the timing up a little, also I'm going to replace the thermostat to 160 , I was living in Colorado for a couple of years and I changed it to 190 for the heater to work properly up there I had a 160 degree before . It pass smog test before but I was just at the edge of failing on the NOX by a few numbers , I think that now that the engine is broken in the compression might have gone up a little , the smog tech also told me that they changed the test a little lower to get these old cars off the street , making it tougher to pass
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Old 11-20-2013, 01:17 PM   #17
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Wow what a response. OBD1 ECM`s are not reprogrammable.....I am working with a couple people to be able to actually change the Eprom so in the not to distant future that might change.....so that is a pointless question. Properly set up there is no reason why a OBD1 controlled stroker cannot run well and efficiently.

Putting a BB in the FPR vac line will cause a lean condition skyrocketing the NOX level.
1) I never said it was programable, I said CUSTOM CALIBRATED...
FYI, some OBD1 computers ARE programmable, you just need to know what you are looking at.

Did you know some Ford heavy duty trucks use a OBD2 computer programmed as OBD1, clear up till 2002!
Early OBD2 systems are used on some 1994 and 1995 vehicles and are programmed with OBD1 calibrations.
If he was using one of these (which IS possible since he is running a newer 4.0L PFI setup), the possibility exists, however since you say Eprom, its answered this for us! (assuming you know exactly what he is running).

2) a BB in the FPR will fool the FPR into WOT (no vacuum to FPR) mode, feeding MORE fuel, remember the more VACUUM the more fuel goes back to the tank, with a BB in the line, no vacuum hits the valve leaving the return shut pushing UP the fuel pressure.....

So, putting a BB int he FPR vacuum line will cause a RICH condition....

the CO reading goes to .04 at 15 mph and zero at 25 mph
Yup, lean

You are on the right track with upping the fuel pressure, but Banthis has a good idea with the timing too, dont go too far or your HC and CO will start to rise.
IMO: lower Thermostat will only result in a small change, and higher octane gas might burn slower, but if you dont have a higher compression (vs stock), you wont get much benefit.

Can you scan and post your test results?
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Old 11-20-2013, 03:04 PM   #18
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Sure I'll try to post all that I can find maybe it will help somebody else's with a similar problem , probably till the weekend, by the time I get home it's already dark outside can't really get much done during this time of the year
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Old 11-20-2013, 10:09 PM   #19
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Yep, I forgot to mention I had an adjustable FPR with my stroker. I can't remember what brand it was though

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