Hiccup

[gectek]

to check the cat you should use the pressure test, but it doesnt sound like a fully clogged cat, maybe partially clogged, but it just sounds kinda funny...i would look for bad connections or a common thread on those 2 occations, like with an apply chart on a trans, if ur trans slips from 2-3 and 3-4 and during a 4-3 downshift, then it is this(if all elec components check out ok), so there seems to be a common point

[Sprucegagt]

Well I don't think your problem is in the ignition system. If it was it would breakdown under high load and you don't have that. Instead you have it happening under light load conditions and its strange that it went away after changing the filter. That makes me think it's fuel related somewhere.

[zhd1000]

is there a way to hook up a tech2 to the car and see what's going on without having any codes??


so i'm thinking it's fuel related too.. so where's the next stop? fuel pump? injectors? where else in the fuels path could be causing a problem?

[gectek]

yes the tech 2 will give the person live data from all of the sensors and inputs.

[zhd1000]

bump.. anyone.. any more ideas?? where should i try next??

[Gizm0815]

Fuel Pressure Regulator

i have been having the same problems and i have hooked up the tech 2 and only found that under light load the #3 cylinder would missfire, at one point in time i had a code 0303 which is #3 missfire but that didn't help, i had replaced the fuel filter, air filter, plugs and wires, did a vacuum check, fuel pressure check, checked FPR and found nothing, so i have an extra set of injectors and i am going to go ahead and change injectors just cause it has came to that point and its not a bad job, most people have been saying since it has 225,000 miles that its a compression problem or valve problem but everything checks out surprisingly well for a 3100 with that many miles so i figured that its worth a shot.

[lone_wolf025]

Originally Posted by zhd1000

bump.. anyone.. any more ideas?? where should i try next??

Maybe its a tranny issue. You mentioned that with the stock PCM it was less noticeable...I assume your DHP jacks up the line pressure? If that's the case perhaps its something that is beginning to fail that is amplified by higher line pressure? How much would it cost just for a pan drop?

Fuel pressure regulator might not be a bad thing to check too like Gizmo said.

[gectek]

well the misfire under light load would usually be spark, thats what was bad on mine, and also the MAF was bad, which irritated the issue. too dirty to clean so had to get a new one, changed those 2 things and that was it

[Sprucegagt]

Originally Posted by gectek

well the misfire under light load would usually be spark,

How so? Light load is second only to idle in no load being placed on the ignition system.

[zhd1000]

Originally Posted by lone_wolf025

Maybe its a tranny issue. You mentioned that with the stock PCM it was less noticeable...I assume your DHP jacks up the line pressure? If that's the case perhaps its something that is beginning to fail that is amplified by higher line pressure? How much would it cost just for a pan drop?

Fuel pressure regulator might not be a bad thing to check too like Gizmo said.

yeah the DHP does increase the line pressure, even though this does occur frequently during (or immediately following) the 2-3 shift, which may suggest something in the transmission, it also occurs at crusing 68-70 mph (don't know about any higher really, i back down the speed as soon as i feel it). so if the problem occurs at a crusing speed couldn't i rule out the tranny?

[zhd1000]

i went to the track on sunday and here are my results.. after the first 2 runs i swaped out my DHP for my stock PCM with the intention of reducing the timing to see if the car would run better... this resulted in fairly same times (the low of the day was with the GM tune though, remembering that i only gave DHP 2 chances too..)

just thought i'd share.. don't know if this will shed any light on anything..

[gectek]

Originally Posted by Sprucegagt

How so? Light load is second only to idle in no load being placed on the ignition system.

because at light load the voltage spikes can start to induce glitches, or agitate a problem. i used a DSO on my car and that is the only way i found it. it was barely there at idle, and when i gave it some throttle, the glitch would show up and get bigger, but under WOT the waveform would be so distorted and change so fast you couldnt tell.

[Sprucegagt]

So what did you change to fix it and how does this imply that misfire under light load usually means its an ignition problem? That sounds to me you had a unique case. Not something that is common.

[gectek]

i changed the 3-6 coil and the MAF as well and it went away...and yah it maybe was unique, but i have seen it before on vehicles with HEI.

[Sprucegagt]

You mean DIS. HEI went away with the distributor.

[gectek]

no i mean HEI. ive seen it with both systems

[zhd1000]

ok i've had my OE PCM in the car since 4/22.. i've filled up with 93 after the track day and everything seemed fine.. today i fill up with Mobil 87 knowing that i had the original pcm in there (and regular was $2.999)... and about 35 hwy miles later that car feels like a dog. could this be related to my problem at all? or is it more of feeling the reduction in timing and using the lower octane fuel?

[zhd1000]

so.. this is still going on.. and i'm starting to get real annoyed with it.. enough to actually do something about it..

where should i look next? all i have done is replace the fuel filter.. so check the gap on the plugs (what are they supposed to be at anyway)? check plug wires? can i check the coils?

[gectek]

the gap on the plugs should be .060 in...says that in ur owners manual i think. also yes u can test the coils, but it isnt a very accurate test because u are testing them without a load on them, but u can still do that. just use an ohm meter. should test little to no resistance on the primary side(small slits) and about 5-9k ohms on the points. but also i would take ur module in to get it tested at an auto parts store that can do that. if that doesnt find the problem, then u should go to a mechanic with an oscilloscope to hook up to the wires while the car is running to look at the wave form patterns. that will narrow it down to coils or module. also if you scan it, look at the maf readings and see what u can find.