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]

:icon_scra 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.:redface:

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?:o

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.

:cheers:
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.:o

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?:icon_scra

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!:mrgreen:

:thumbsup:
Tom

[32valvZ]

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

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?:icon_scra

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!:mrgreen:

:thumbsup:
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 :mad:

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

[tomtom72]

:wave:John,

Yes the T1's are the nuts.....but I must confess I've given up as that budget is no longer valid!:sign10:.......but when times were good I was willing to go that high if I could get one with most of the software for our cars....jez, they have software for every darn system on the car....sweet stuff! I kind of keep looking half heartedly.

I just had a BFO.....actually I just read your sig.....outside shot, do you still have the old chip? Did you try swapping the old one back in just to see if the same miss occurs.....just grasping at straws..:redface:

I just can't quite figure how the clogged MAP hose makes your car do what it does? I would expect a more stable mal-function? I mean if it's clogged, it's clogged....and therefore there is no vacuum signal so then what?....the ECM reverts to a pre-programmed fuel & spark table?.....instead of having real time vacuum readings to determine engine load demand and what to do with pulse width?......jez, I wish I knew & understood more!:mad:

Anyway, I hope you can figure this one out. Be well & I'll keep watching to see what turns up & if I have anything that may contribute, you know I'll post up!

:cheers:
Tom

[32valvZ]

Well, I took her out for a spin after work today, and it did well. I couldnt simulate the problem. Got it nice & warm, drove it about a 15 mile trip. I did everything I could to get it to do it again, and it just wouldnt. Before, it was doing it about every other time I up shifted. Not saying its fixed, but it sure didnt do it today!

As far as the old chip, no, it was a trade in to Marc. The stuff that was in the hose was weird. It was a really gummy oil, to the point of being sticky and thick. That combined with a soft hose, maybe the problem. Perhaps when the engine warmed up, the hose was collapsing and that gummy oil was sealing up the passage?? I'm not sure, and I'm also not sure if changing the hose did the trick.

I'll take it out this weekend for a long drive and see what happens. Thank you for your help and good ideas.
John:cheers:

[Jeffvette]

It wasnt plugged completely, but it was definitely gummed up inside the hose.


There is a reason why GM made that hose plastic. Rubber gets saturated and starts deteriorating collapses.

[tomtom72]

There is a reason why GM made that hose plastic. Rubber gets saturated and starts deteriorating collapses.

thanks for turning on the light Jeff!:thumbsup:
So if our motors didn't have so much oil vapor flying around this wouldn't be a maintenance issue....the oil in the map line.


John, good deal. Go play with the toy!:thumbsup: