New motor, new cam.. starting/running issues

[neonhomer]

Rebuilt the motor for my 96 ZJ. Motor is stock, except for the Comp cam and the "703" injectors. A lot of things were replaced, but with stock replacements.

Anyway, the Jeep will, 90% of the time, fire up on the first try, and runs great...

The other 10%..... Sometimes it acts like the old "no fuel at the injectors" bit. However, I have checked, and there was fuel pressure at the rail. Usually when the jeep does this, just holding the throttle open 1/4 will let it fire right up.

Then... My exhaust is getting hot... okay, hotter than normal. Example. Other day, had to drag my friend out of the mud. While pulling him out, I heard a pop through the intake. Anyway, got him out... and he broke an axle. Got some rope from under my pass rear seat, and noticed the floor was hot as hell!....

I am thinking I need a way to tune this motor. The OBD-II system is okay at part throttle, but when I go to WOT, the fuel maps seem to be lacking for this setup.

I am in the process of building a MAP adjuster, but I'm getting conflicting info on if it will do me any good....

[Muad'Dib]

Backfire out the intake is usually a sign of running lean.

Did you use refurb injectors or Junkyard ones? One or more could be sticking.

I had trouble with refurbs and had to purchase new.

[neonhomer]

These injectors were from the junkyard, but were "refurb'd" myself with new screens after flowing FI cleaner through them. They all performed flawlessly.

I am thinking the motor is running lean, but I am not sure how to richen it up. The 703 injectors flow a little more, and I have relocated the IAT to the air intake tube.

The PCM will adjust the fuel at part throttle, but I need to be able to add fuel at WOT.

There are no tuners that really work for the 96 ZJ, that will let me adjust the WOT fuel maps.

Looking for ideas.

[SilverXJ]

96 Is OBD II, so there are quite a few adjusters. Off the top of my head the Apexi SAFC II, Splitsecond FTC1, AEM FIC. But the first step would be to get a wideband to see the AFR. I would also be hesitant that the injectors may still be clogged.

As always, check your distributor indexing just to be sure. http://www.angelfire.com/my/fan/dist_index.html

[neonhomer]

When we rebuilt the motor, we replaced the distributor with a new one. We followed the procedure in the FSM for the distributor, and it was good.

Like I said before, the motor runs great at part throttle. Get on the throttle, and that is where things get dicey....



I've been looking at the Unichip device. According to them, I can use their plug & play kit for the 96-01 XJ.

[SilverXJ]

The unichip you can't tune yourself and according to Hesco there have been quality and supply issues with them. What cam did you use?

[neonhomer]

Comp 68-232-4

http://www.compcams.com/Company/CC/cam- ... id=12&sb=2

[SilverXJ]

I don't know how the FSM differs from the link I posted, but sometimes you need to break off the ears on the distributor to set it correctly with an after market cam.

[dwg86]

Did you use stock springs with that cam? You might have some valve spring coil binding issues with stock springs.

[neonhomer]

No. I had a machine shop set up the head for the cam, so he installed the appropriate springs.

Distributor is lined up where it should be, according to FSM and by timing.

Two things I noticed today. With my scanner plugged in, I am noticing a -14.5 LTFT.

Also, at WOT, the upstream O2 goes lean, and maxes out at .88v (or something like that). Spark advance maxed out at 22 deg.

[SilverXJ]

Rich is up around 1 volt, lean is down around 0 volts. .88v is rich.

The distributor doesn't control timing so verifying it by timing won't work. It does however control the fuel injector timing.

[neonhomer]

Well, the aforementioned article has checking the dist by where the rotor is pointing w/ the balancer at 0 deg. I don't think the distributor is at fault.

Then either my scanner is not interpreting the data right, or something. The scanner goes 0.88v at WOT, when you let the throttle close, it goes to 0v.

If it WAS running that rich, I would be rolling black smoke from the exhaust.

For the record, the scanner I am using is a Snap-On MT2500 using the appropriate cartridges. (Non programmable, but good up to 97).

[SilverXJ]

Well, the aforementioned article has checking the dist by where the rotor is pointing w/ the balancer at 0 deg. I don't think the distributor is at fault.

I haven't looked at the FSM, but is that what it calls for? The only reason I am concerned is that frequently with an aftermarket cam you may need to rotate the distributor a bit to get it to install correctly.

Then either my scanner is not interpreting the data right, or something. The scanner goes 0.88v at WOT, when you let the throttle close, it goes to 0v.

That sounds normal. Rich at WOT and then very lean with closed throttle at RPM.

If it WAS running that rich, I would be rolling black smoke from the exhaust.

The problem with the stock O2 sensors (and all narrow band sensors) is that they really only have 3 data points: 14.7:1, lean and rich. You can't really tell how lean nor how rich. So, rich to it is anything below 14.7:1 or so (numerically lower). Same for lean.

Next time it doesn't start you may want to throw a noid light on an injector to see if you are getting a injector signal. Or see if you have spark as well. Is there any rhyme or reason to the no start issue? i.e. if then engine ishot or if its cold?

[neonhomer]

No. There is no rhyme or reason to it.

My Jeep normally sits during the week, because I drive a company car. The only time it gets driven is either when I have to go get my girl from work or late night Frosty runs, or on the weekends.

I've thought about it maybe being a fuel pressure issue (not building up). I can cycle the key numerous times to build pressure, but it doesn't do anything to help. Hold the pedal down 1/4 and it will fire right up.

The data doesn't add up. The overly hot exhaust, popping through the intake, it all points to a lean condition. The data from PCM is conflicting as well. The O2 sensor says .88v, but the "indicator" (which will go from rich to center to lean), will go LEAN on WOT.

At this point, an expensive tuner or fuel manager is out of the question. No money. I'm hoping the MAP adjuster will help, but once again, conflicting data.

[SilverXJ]

No. There is no rhyme or reason to it.

My Jeep normally sits during the week, because I drive a company car. The only time it gets driven is either when I have to go get my girl from work or late night Frosty runs, or on the weekends.

What about the ambient temp? I've delt with rough starting issues and it was worse when it was cold out. I have a 2000, which should be more restrictive in terms of the AFR. I have had the 68-232-4 cam and never had an issue with. I only started to have starting issues when I went with a more aggressive cam.

I've thought about it maybe being a fuel pressure issue (not building up). I can cycle the key numerous times to build pressure, but it doesn't do anything to help. Hold the pedal down 1/4 and it will fire right up.

What happens when you floor the pedal during start up? The PCM will kill fuel when you floor the pedal during a start to clean a cylinder floor. I wonder if it dithers that on % of the TPS. Thinking about it, it could also be a lack or air issue. Hesco does recommend drilling a hole in the butterfly to compensate for the extra air flow requirements of the stroker. But usually if you have issues. Does your snapon scanner allow you to see data on the IAC?

The data doesn't add up. The overly hot exhaust, popping through the intake, it all points to a lean condition. The data from PCM is conflicting as well. The O2 sensor says .88v, but the "indicator" (which will go from rich to center to lean), will go LEAN on WOT.

a rich condition can cause the same thing with extra fuel burning in the exhaust manifold. As well as an ignition timing issue. What does the O2 sensor show at a hot idle and at a constant cruise RPM? Also, on your narrow band gauge could you have wired it backwards? I've never used one for the previous reasons, but it doesn't correspond to the voltages from the snapon scanner.

At this point, an expensive tuner or fuel manager is out of the question. No money. I'm hoping the MAP adjuster will help, but once again, conflicting data.

Your fuel trims are a bit out of wack, but shouldn't be causing the issues you are having. Prior to a tuner I would get a wide band gauge, but that isn't cheap either.