Developed a miss......

[32valvZ]

Only seems to happen at part throttle. If I'm coasting or I'm between gears then ease into the throttle it misses pretty badly. Its almost as if one or more cylinders just stops firing..... then suddenly, it all catches up and its fine until the next time it feels like doing it. Its pretty random, but getting more frequent. Having trouble determining weather its fuel or ignition related.

Heres what Ive done so far.

Pulled all the plugs... they look like new.

Checked fuel psi.... its 40 KOEO & 40 running, doesnt ever seem to bleed down past 38 psi

Checked for codes..... found a code 13...... checked the o2 wires, the o2 extension harness, and pulled th o2 on that side. It all looked ok to me, nothing unusual.

Pulled the air horn and looked into the throttle body to observe the butterlies..... all 3 looked like they were functioning properly, and the back sides were clean still from when I cleaned them during the plenum pull.

NOTE** all the injectors, coils, plugs and wires are under a year old, as well as the fuel filter.

Any ideas on where to go next?

[tomtom72]

hummmmm....I hate intermittant stuff. The fuel PSI #'s look a bit on the low end of the FSM listed range? Clogged strainers in the tank? You checked the regulator hose for gas?....long shots, I know.

what about:
Are the O2's new? How are the m/volt and cross count readings?

Excessive oil in the MAP hose and therefore in the MAP vac port?
Also the electrical side of the MAP? The voltage is suppossed to change with changing vacuum.

TPS, I would want to check if it was going thru it's voltage sweep in a linear fashion....ya know from .54 @ idle and it changes correctly as you advance the throttle.

It will not do it if the car is running with a scanner on it in your driveway? I was thinking that if you could duplicate the miss with the scanner hooked up you might see something in the O2 #'s or the fuel #'s....and you could check the MAP and TPS voltage responses. Sorry I'm full of answers, hugh?

If it were me I would redo the fuel pump test, scan the car, see if I could get it to miss in the bay so I could smell the exhaust....might tell ya something. I usually keep last yr's plugs....I use the std GM 402's...so I'd swap them just to see. I'd do a spark intensity check. Re check all my EEC plugs and then be lost if I didn't find anything.....oh battery & alternator voltages just to be sure because it sounds like it has to be hot for the miss to occur, right? That's the nice thing about the scanner, hook it up & let the car get hot and watch the outputs.


Tom

[32valvZ]

Thanks for the input Tom..
I'll have to check the map hose.... The o2's afe new, (like a yr old) I dont have a scanner, just a multi-meter.... What scanner are you using? I tried more than once to buy an OBD1 and never could complete a transaction. I dont really feel like spending 5 or 6 hundred dollars on one either. I know this is probably not an expensive fix, just a hard one to find.

I thought about the TPS also. I guess theres some kind of rheostat type mechanism in there that can wear down in a certain spot and cause this kind of problem.

[32valvZ]

Got home from work this afternoon and took the hose off the map sensor. I blew through it & was met with a bit of resistance. I blew a little harder & heard whatever the blockage was free up. I pushed a small dowel through it and a bunch of "caramelized" looking oil came out of it. Real gooey. I also noticed the hose was pretty soft. I replaced the hose and put it back together, but havent had a chance to test drive it yet. Heres to hoping!

[tomtom72]

Okay, sorry I haven't gotten back to this in a timely fashion.

Good on the MAP hose! I often wonder if the oil is able to get up into the vac port and get inside and do some kind of "damage" to the internal workings of the MAP? If it was plugged solid, wonder why it didn't set a DTC?

On the TPS, I was thinking that it has to be built like a dimmer switch...so yea a rheostat was my visualization also....bad contacts & all.

I have an old snap-on MT2500 scanner I bought used from a retired mechanic. I got what I thought was a generous deal from the guy, $200. The rub is the software which is to me expensive. I have basic emissions/motor trouble-shooting software. I bought the anti-lock software cheap on e-bay, it was about $40.00 if I remember right. I kept loosing auctions on Tech1A's....seems everytime I found one to bid on with good software packages for our cars, I would reach my $1,000.00 limit and loose out to a more determined bidder. The Tech1A is the one to have IMHO, because I think the FSM's 6E section is written around that scanner. What I have is very useful, when I get a DTC it makes "seeing" what's going on a breeze.

Good job on your part, now go get some quality testing time with your baby!


Tom

[32valvZ]

Originally Posted by tomtom72

Okay, sorry I haven't gotten back to this in a timely fashion.

Good on the MAP hose! I often wonder if the oil is able to get up into the vac port and get inside and do some kind of "damage" to the internal workings of the MAP? If it was plugged solid, wonder why it didn't set a DTC?

On the TPS, I was thinking that it has to be built like a dimmer switch...so yea a rheostat was my visualization also....bad contacts & all.

I have an old snap-on MT2500 scanner I bought used from a retired mechanic. I got what I thought was a generous deal from the guy, $200. The rub is the software which is to me expensive. I have basic emissions/motor trouble-shooting software. I bought the anti-lock software cheap on e-bay, it was about $40.00 if I remember right. I kept loosing auctions on Tech1A's....seems everytime I found one to bid on with good software packages for our cars, I would reach my $1,000.00 limit and loose out to a more determined bidder. The Tech1A is the one to have IMHO, because I think the FSM's 6E section is written around that scanner. What I have is very useful, when I get a DTC it makes "seeing" what's going on a breeze.

Good job on your part, now go get some quality testing time with your baby!


Tom

Hey Tom, no need for apologies my friend. Yea, I was wondering the same thing about the map being damaged. It wasnt plugged completely, but it was definitely gummed up inside the hose.

After this, if its still sick, I need to get a longer hose for my fuel psi gauge so I can observe it during the miss, while driving. Unfortunately, the hose that came with my set is only about 2' long.

I know what you mean about the T1's.... they always got pricey on Ebay, so I gave up. Then another time, a guy on here was gonna sell me one with everything I needed, and he backed out

Thanks for your help, and I'll keep you posted.
John