Having problems with the new cam.

[Ttop34]

Right now I have 5 of the stock Delco Platinums in there with one NGK TR-55-IX gapped at what it had when it came from Thunderracing, .050

I have some regular TR-55's on order, hopefully will be here monday. So should I still get the walbro fuel pump or is that not the problem? That intake work and head work are the only differences between my car and Min's and he's running fine.

[strange_trp]

i'm not exactly shure the problem is severe knock retard. not likely to be the main problem anyway. to rule this out, run some racing gas (super-high octane) in it and see if it gets better... my first thought is that you're getting too lean at high rpm's. you need to fix this before you burn a valve.

i think there may be a few possibilities:
1: with your new cam, your fuel pump may not be able to deliver adequate fuel volume at maximum injector pulse width. with autotap make sure your injector pulse width is not cutting out and make sure your desired a:f mixture at WOT is somewhere between 12:1 and 13.5:1. i think that if you find all this stuff good, your fuel pump is just not delivering enough volume at maximum injector pulse width. although a higher-volume pump (pump makes volume, press regulator provides restriction that allows for pressure.) may help if you're getting very lean at high rpm's, it still will not address your DTC problems.

2: changing cam profile like you've done, you really need to get pcm reprogrammed. it is trying to fire injectors and ignition to run an unmodified engine. yours has been modified significantly and the pcm needs to know that there will be more air coming in and less exh backpressure so that it can make corrections for fuel delivery and ignition timing, as well as egr solenoid operation and expected o2 sensor response. look through the past year or so at everyone that has done major engine mods (or even just exh mods and put in 0s sims) without reprogramming pcm and like 99% of them are posting with some kind of drivability problem or some kind of "my light is on" problem. the pcm has to know what the engine is doing mechanically so it can make the proper decisions electronically. part of the EPA ob2 mandate is that the pcm periodically test sensor operation by purposefully going way rich or lean and observing 02 response. sims wont see this and wont send the proper return signal so the pcm sets a code.

3. like the others suggested, replace all rocker arm bolts, etc that you removed. they are "torque-to-yield" bolts and are designed to be torqued only once.

4. get rid of the o2 sims. waste of money. the pcm will expect to see the post cat o2 get slightly rich if the precat 02 sees very rich, and post cat 02 should get slightly lean if the precat o2 is very lean. the o2 sim sends a constant non-varying ac voltage signal to pcm that does not respond whatsoever to fuel mixture. in fact, to ensure proper operation of catalyst efficiency monitor, the pcm will sometimes purposefully richen or lean the fuel mixture jsut to see if all o2 sensors are functioning properly. if the postcat o2 is a sim, it won't see this and the pcm wont see the proper response. so it will set a code.
put old post cat o2's back in and reprogram pcm for wider acceptable parameters for the catalyst efficiency monitor.

all i have time to write right now (grades are due in a few hours). try these and see what happens. "bolt-on" mods are rarely just that anymore. to get real performance from mods you have to let the pcm know that you have changed things so it can make the correct decisions electronically. otherwise, you often get poorer performance, increased fuel consumption, possible engine damage, and dtc's.

[strange_trp]

<blockquote>quote:</font><hr>Originally posted by slacker69:
yeah thats KR all right cause the colder it is the less of a chance u have for premature detanation.<hr></blockquote>

not necessarily. at WOT, the pcm goes into open loop and the engine coolant temp sensor is one of the main inputs the pcm uses to determine fuel delivery (as well as MAF, MAP, RPM, and TPS). i am thinking lean mixture at high rpm's, either because of insufficient pcm commanded injector pulse width or insufficient fuel pump volume at WOT and high rpm's. at warmer temps the pcm will not let the a:f mixture get as rich as it will at colder temps (colder temps the pcm will richen the mixture to ensure enough of it vaporizes to ensure combustion.)
severe detonation will also probably set a separate dtc.

but let me qualify my suggestions by saying that an engine running way lean will have higher combustion chamber temps which may result in preignition. however, the preignition/detonation in this scenario is not the root cause of the problem. it is a symptom of the core problem of fuel starvation... just going to a colder plug will solve detonation but won't help power loss because you're still going to have a leaner-than-desired fuel mix.

[ December 19, 2002: Message edited by: strange_trp ]</p>

[Ttop34]

Steve, Thanks for replying. I won't have Autotap untill I get back to Lubbock on the 30th unless Dee will scan it for me, I'll email him as soon as I get home. I'll also try to steal/borrow a torque wrench from my dad when I'm home and put in all new rocker bolts when I get back to Lubbock.

So everything that I can tell points to me needing a better fuel pump. Do I need to go to the walbro 255 or will the 190 be more than enough? I've been told the 190 will last longer and not get as hot.

Thanks again for responding, your insight has been missed.

[nino]

if he is getting lean at high rpms, would adjusting the a/f ratio with a maft+ help that situation?

[strange_trp]

thanks for the compliment, kendall... let me know how things work out... i've been painfully busy lately.

nino...
the maf+ will only help if the pcm is commanding incorrect injector pulse width for the proper mixture with the greater airflow (due to cam.) if it is lean because of insufficient fuel pump volume the maf+ won't help much.

i miss you guys :( married now, with a couple of kids and a couple of jobs... i hardly have time to wipe after dropping a load [img]smile.gif[/img]