2_point8_boy

Ok here's the deal. If I let my car idle for a minute, like at a light or something, then when I get back on the gas it seems like it's misfiring or something, but once I get above 2000 rpm, the problem goes away. i've done the entire TomP tune up and it didn't fix a thing. Fuel pressure at idle was right at 45PSI and went up steadily as I opened the throttle. I even did a vacuum check and got 15in without and variation, not even a little bounce on the needle, and that acted fine with throttle changes. EGR valve is fine as well(checked w/vacuum pump for diaphram leakage and to see if the motor slowed when it was opened manually...it did) Now I just don't know what to check. It does smell like it's running a little rich. Let me know what you guys think. Thanks in advance.

Jeff

Gumby

Might be time for a dist rebuild. It would wooble in the bushing easier at lower rpms. Also you could check your cap index. cut a hle in an old cap and amke sue the tabs line up when it fires. Some time they get out of wack and the rotor and cap contact doesnt line up as best as they could. Even though the car may be timed right. The tab should be right across / even with each other when it fires.


Matt

85f-bird

MAF? i know it caused me some probs at different times, one of which had a hesititation and backfire issue at the lower RPM band, but was fine as power increased, although there wasn't anywhere near the power i wish it had.

2_point8_boy

MAF is a possibility. I have to go and find TomP's write up on how to check. If anyone knows exactly where it is and can save me the time, that would be awesome. Thanks, and keep the idea comin'.

2_point8_boy

ok, here's the results of a few other tests I ran and some other info that might help me out in the quest for the problem.

I hooked up my fuel pressure guage and key on, motor off, hit right at 40 PSI. Motor running was just under 40, maybe 39 PSI. Worked fine through out the throttle range. 40 PSI all the way to WOT and held it.

I also hooked a vacuum guage up to the bad boy. Manfold vacuum held a steady 17 at idle, no fluctuation what-so-ever. WOT equals 0, just like it should, then with the throttle snapped shut, it went way up to like 26 or so, then came back down as engine speed decreased. When the throttle was slowly opened, there was a steady increase to about 26-ish or so. AlL of this stuff is normal.

I also noticed that the problem only exists after the motor has entered closed loop operation (I think that's the mode where it listens to the O2 sensor), signaling the end of cold start condition. During those fist couple of minutes, the car runs beutifully. This makes me wonder is the coil is weak. If the coil is starting to go, then it can make enough power to jump the richer A/F mixture that exists when the engine has just been started, but when the computer adjusts for the proper mixture, there isn't enough voltage to make the jump across the plug.

I have to check the coil next. If that brings up nothing, I think the TPS is next on the list, since the problem goes away with a little jiggle of the throttle. Let me know whaat you guys think, I need all the input I can get.

Gumby

MIght wanna find a real dark street somewhere n pop the hood and check for spark leak.

Matt

AGood2.8

1st off- has it always done this or is it something new?

When did you last change the plugs? What type of plugs are your running? Plug wires? Check their resistance-could be bad a lower voltage. Thats starting with the basics- usually the problem is found there.

How old is the Alt- whats the gauge doing?
To check the MAF, just lightly tap on it with the car idling. If the motor stubbles when MAF is tapped on then replace it.

What octane fuel are you running? If running 91, try 87. Higher octane can cause a car to stumble off the line at low r's(especially a worn motor combined with weaker ignition parts.

Lets start here first. A car will run better when lean, not rich. However, a coil will conduct charge stronger when cold than hot.

2_point8_boy

The problem is something new.

I live on a REALLY dark street. When I look under the hood, it doesn't remind me of 4th of July, so that's a good thing. The Alt. is less than 3 months old. The voltage jiggles a llittle all the time, but I can't figure out why. It's done it since i bought the car. I think it's just the connector to the voltmeter because it doesn't affect the battery or lights or anything. Never goes under 12 volts though.

Plugs are a few months old, and the wires are about the same age(8-10 months I would guess, can't remember for sure). I always run 87 octane(poor white boy living in the San Fernando valley, do you really think I can afford a tank of 91...)

I still have to check the MAF and the color of the spark. I also have a MAJOR exhaust leak on the passenger side of the motor. The damn bolt back by the firewall keeps comin' loose. I think I might Loctite it tomorrow.

Gumby

I have found out with both my 2nd and 3rd gen that they can eat a new tune up fast. Sometimes even though its not even close to time for a new full tune up, its fixes the problems.

ON my 2nd gen I went through hell changed everything in the ign, had problems for weeks as it ran fine till I went to stop. SOme 98 cent champion plugs fixed it but was the last thing I tried as it wasnt near time and the old plugs were clean.

My 3rd gen did the same thing. I ran in circles with codes. changing relays, checking fuel pump, went through 3 stock coils and just threw money and time down the whole when again some plugs n wires fixed everything even though it was no where near time for it.

Matt

2_point8_boy

yeah, just my luck that's the problem. It's just kinda weird how it'll run like crap when I get on the gas, but if I let off and get back on, then it's fine and I can pass most anyone. It's also kinda weird that it only happens once the engine has run for a couple minutes.

Keep the suggestions comin' everything helps. Thanks Guys.

AGood2.8

2_point8, You didn't mention what type of plugs you are running- note to all, do not run A/C rapid fires or Bosch platinum 4's. Even the stock ignitions systems on our cars are too hot for them, they burn up fast. I tried Rapidfires last time to see what the hype was- they sucked to begin with, then faded fast after 1 day of driving. Bosch lasted me about 2 weeks. I am now running double platinum Autolites (Have always used Autolite regulars in all my cars for years. Even my 540hp race vette- they are workhorses) The double platinums work great and have been in there now for 2-3 months with no performance drop what so ever. I even run a VERY hot ignition in this car.

Doward

I've always run the $1.59 AC Delcos from Autozone. Awesome plugs for the $$.

Gumby

I like the accel u grove plugs. They seam to last forever.

Matt

2_point8_boy

Running good ol' cheapo autolites. I've never had a problem with them wearing out too fast, but I have had a couple beak off on me.

2_point8_boy

OK, so i fixed my problem. It ended up being the plug wires. The bolt on top of the exhaust manifold keeps coming loose and the exhaust gas leaks out in a straight shot at the wire there. I replaced the wires and BAM! Problem gone. I also fixed the exhaust leak and tightened that bolt down nice and tight, so hopefully i wont have another problem with it. I am using my "spare set of wires right now, but when I go buy new ones, I think I'm gonna pop the money and get the good wires (Accel 8.8mm and the like) so that I get the lifetime warranty.

It's kinda funny too because opening the hood didn't remind me of 4th of July. I guess that the excessive heat wore them out and when they got heated up the resistance went up, which would explain why I had no problems when the car was cool, but once it heated up, i wasn't firing right.

AGood2.8

Don't buy Accel wires- they are crap. The boots crack very easy. Get a set of Taylors and some firesleeves for the boots. That way you will never ever have to buy another set of wires.

By the way, was it the #3 wire that went bad? the one by the EGR? They go bad first generally because of the extra heat radiating off the EGR.

2_point8_boy

Well, glad to hear some kind of feed back on the wires. I usually just go down to Pepboys/Autozone/Tampa Auto Parts and buy whatever the "custom fit" wires are. Never bought a GOOD set of wires.

No, it wasn't the #3 wire, it was the #5. The top bolt on the exhaust manifold right there came loose and the hot exhaust was shooting right up onto the boot. I had those little metal "heat sheilds" that fit right over them, but I think they more helped to cook it than protect it.

Stupid California smog laws, I wanna get a set of legal headers that are heat coated. That's what I really want. Christmas list I guess, for like 4 years from now.

jeremy178

don't think that headers will help your problem w/ cooking wires, one of my friends runs a built 427 under his hood, and those headers cook everything near them

2_point8_boy

Headers will probably help as compared to the stock manifolds because they will 1: Be heat coated, helps drop the temp a little, and 2: They tend to pull away further from the block then the stock ones.

Now I'm not saying for sure that they will help, but hey, it's a good excuse for me to talk the woman into letting me get headers. I can hear me now, "sure, they're expensive, but think of how much less I'll spend on wires "

jeremy178

hehe good thinkin'

nadster

I actucally had one melt in half and break on me one day shorting out the rotor/cap and burnt out the air temp sensor as well from the zap to the block.

-Dan

Nixon1

On my 302 that has equal-length shorties (whoever invented these should be shot) I had a boot on an MSD wire, which had a heat-resistant sleeve over it on TOP of MSD's normal heat resistance....well the boot touched the header, melted, and grounded spark right into the header. Car stumbled and missed so bad I thought I was going to kill my engine. I ended up stuck in Orlando for the night til I could get a new set of plugwires the next day.

SharpSnake

sounds like mine here what im having problem with

yesterday i was driving around town all day the car was fine i was done to a 1/4 tank of gas and i stoped to fill it up so i did and i put in a bottle of gumout fuel injecter cleaner and the payed and drove off about a mile down the road i stoped at a red light i had a ich on my foot so i stepped on the brake pedal real hard and rubbed the side of my foot and about that time my car stared runing real rough and then died i tried to restart it and it just cranked cranked cranked and no start after i sat through a green light i tried to restart it again and no go just crank crank crank after a another green light ppl behind me was getting pissed i tried to start it again this time it cranked cranked then spudderd and spudderd the started real crappy backfireing and could not run it passeed 2200 rpm so i limped it to a parking lot and opened the hood and checked things out and when i hit the trottle lever it bogged badly and a puff of black smoke come out of the left side either fome the tube that comes out of the throttle body to the valve cover or the egr valve now today in the morning i had to crack crank crank spudder spudder spudder backfire backfire zroom then it idles ok but i have no throttle responce if i rev it up it goes boggggg zroom and after it reaach 200 220 degrees it all worked fine no hesitation or anything so can anyone tell me after reading this long post what might be wrong with it and what the simplest steps to find out

SharpSnake

sorry its a 90 firebird 3.1 mpfi

TechSmurf

Could be over-filled gas tank, evaporative emissions canister system failing.. happened on my 305, where if I filled her up too much, she'd suck raw fuel in through the vacuum line attached to the EECS (btw, EECS should be vapor-only, not liquid fuel.. this is a sign of a serious foul-up of the system) ... Pulled EECS, and the fuel line started siphoning my tank out.. I'm sitting there going 'WTF? This is a vapor system!!' ... long story short, capped vacuum and plugged fuel line and completely removed EECS, car's run beautifully ever since.

2_point8_boy

from the puff of black smoke that you are talking about, it sounds like you might have a clog somewhere. i had my catalytic converter melt and clog on me(no one knows how old it was), but it wouldn't let me get and kind of pwoer and wouldn't rev past about 2K. i think the only reason that the car actually still ran at idle was because i had an exhaust leak that was letting just enough exhaust out to keep the backpressure down to where the engine would still run. long Story short, it sounds like it's a clogged cat, or maybe even a clogged PCV system.

TechSmurf

Clogged PCV won't keep a car from starting.. the IAC will spend a little time compensating, however it's not that drastic.. clogged PCV will, on the other hand, cause lovely things like fuel vapor buildup in your crankcase, effectively turning your oil into a corrosive sludge, and the pressure buildup will cause it to vent wherever it can, being out the PCV inlet filter or blowing out the dipstick.

Melted cat, yep, that'll do it.

You might also want to check your codes.. if it was a TPS problem or something, chances are your ECU has some nice info for you.

SharpSnake

i get no codes i tested the codes with a reader and all was well i have been driving it all day im going to change the fuel filter in a few mins and ill see what happends tommorrow morning

TechSmurf

EDIT: post removed.. on second thought, after finishing the mounting brackets for my intercooler today and glancing at how the V6's EECS is set up, there's just no reasonable way to diagnose it.. why the heck does it need 3 vac lines?... argh.