alright...this definately is getting annoying. for those of you who read my last post about my hesiation about threee weeks ago you may remember the story. but anyway. my car had been hesitating for a while, so i removed my rapidfires and gapped them back down from a .055 to a .045. but that didn't solve the problem. i also changed the fuel filter and that didn't help either. so my parents sent it to the dealer and they changed out my distributor and my 02 sensor. they said they were water logged ( i had water up to my doors once).

so we got it back and they said there was a small hesitation but they didn't know what it was and that i should remove all my performace parts.....hell with that!! well anyway, the hestitation was gone until about a week ago. now when i gun it the car just jerks...almost like only some of the cylinders are firing, and then catching. well anyway....thats the problem and so far the following has been done:

MSD gm blaster coil, MSD superconducter wires, ACdelco distributer, O2 sensor, fuel filter, +4 plugs.....any other thoughts??? its not my egr valve, the 3.1s didn't come with them according haynes, they were digital in the ecm. and the timing is set at 12*..i am assuming the dealership did that - i havenever touched my timing.

the car has 93,000 miles on it now and has run beautiful to this point...so i am picking at your brains....watcha think?



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1990 Firebird 3.1
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- Auto Trans, TA Body Kit
- Home Made C.A.I.
- ASP Underdrive Pulleys
- MSD 8.5mm Superconducter Wires (custom-cut)
- MSD GM Blaster Coil
- AC Delco Cap & Rotor
- Bosh Platinum +4 plugs
- Mobil 1 Synthetic Fluids
- 2.5" Hooker Aero-Chamber Cat-back
- 2.5" Hooker Elite Stainless Extension Tips
- GTS Blackouts (stickers removed)
- TB Bypass

KILLS = Dodge Daytona (stick), 2000 Toyota 4 Runner 4WD,
1997ish Ford Explorer, "older" Jeep Cherokee (don't ask why they are all SUVs...who the hell knows?)

LOSSES = 300zx (had him half way through 2nd, he was manual)

"The racing dice added 5hp...I SWEAR!"

 

Put the timing at 10 degrees and see what happens... what kind of water were you in? Fresh water or salt (more corrosion) water?


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

it was a while ago, a river at school flooded and a friend had moved my car. when i went to check there was water up to the bottom of the doors....about 1" or 2 on the floor....so i got in, started it (grinned while i did, wasn't sure if it as the best idea) and gunned and got out. then wet-vaced it. but it was fresh water. about a year ago.

 

any ideas? anything to look for?

 

Ever change your trans fluid & rear axle fluid? Both of those guys have vents on the top; you might've gotten some water inside. The trans I don't see as likely; the vent's on the top of the case, before the upward curve of the bellhousing.

How's everything look now? Like, the spark plug tips, the inside contacts of the distributor's cap & rotor, air filters, etc? If something's worn down it'll point to a problem. Plus, you might be able to find a bad cylinder (aka leaking/clogged injector) by reading the plugs. Since you can't tell the gap of those Bosch +4 plugs, maybe you can throw in cheap $0.99 AC plugs for a while to help you diagnose the problem.

Got a fuel pressure gauge? If not, it might be time to buy/rent/steal one and throw it on.. don't wind up like I did (with my pants down at the racetrack)! Stock "prime" pressure (key to "on", engine stopped" should be 40.5-49 PSI.. I saw one book even say 35-39 PSI.

I can't think of much else that hangs "that low" to be affected by water.. even your gas tank vent is way up there, a few inches above the axle.

Check all your plug wires with an ohmmeter.. they should come out to be nearly the same (except for the shorter coil wire). The MSD 8.5mm wires are 40-50 ohms/foot, so if you've got a 3 foot wire that reads 500 ohms, you know it's bad. Yeah it might not be 100% bad, but if every other 3 foot wire shows 130 ohms, and your one wire's at 500 ohms, the car might be running a little off.

It honestly sounds like something small & stupid... unless it's the fuel pump. Did the dealer ever check fuel pressure?

[edit] Any sudden change in temperature in your area? We in NJ went from hot/humid weather to cold/dry weather in a day; and I'm getting a sore throat as a result. (fu@%!) A sudden change in temp might point to a bad CTS, coolant temp sensor...

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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

[This message has been edited by TomP (edited August 01, 2001).]

 

hey TomP, thanks for the help so far. sorry if this gets long, and i don't expect you to have all the answers, just giveing up some more info i am gonna tinker around this weekend.

i already tested my wires about three weeks ago before it went to the dealer. since i custom cut them i wanted to make sure it wasn't them. they all matched, and read good. something like 95 ohms for a two foot length. my tranny fluid was changed before the flood thing, but still looks good. also, my oil is a nice brown color (due for a change soon)....i was reading around the board and saw that if it looked like "chocolate milk" then i may have a head gasket leak from coolant leaking around. i also read that if you pop the radiator cap and run the engine and you see bubbles that may be a sign of a head gasket leak too....luckily no bubbles.

two things i should add. one, i ran out of gas about three months ago, since then i changed the fuel filter. it was definately the first time its ever been done, and the gas that came out looked like and off white color, definatley dirty. also, fuel injector cleaner hasn't helped...but what is dry gas??? i read about it the other day.

and the last thing, how would a leaky exhaust manifold affect performance? my passenger side has a leak. while listening to it though i also notice with a quick opening of the throttle the engine definately stumbles when it is warm...and after listening for a while i am noticing a quick knock until it catches...then the engine runs great on the top end. i don't know enough about cars to know what might cause this.

anyway, i don't expect you to have all the answers, but maybe some suggestions since you have more experience than i do. for now i think a fuel pressure gauge may be a good investment and i am gonna throw my rapidfires back in this weekend. let me know what you think....thanks a lot!!

 

Hey, no problem! (Besides, I like a long post, in case you couldn't tell, haha) And dude, I hope it's not the pump- if you run a fuel pump dry, you can burn it out... in fact, it's not good to run with a low tank of gas. The pump gets hot; and when you have a full tank, the pump is submerged in gasoline- and it stays cooler. Dry gas has some alcohol in it, and is meant to take water out of your gasoline (to make it "dry"). You usually just need it in winter, when it's cold outside, since condensation forms inside the tank.

I'm not too clear on what a leaky manifold means... maybe someone else can help. I'm guessing it could be one of two things- the leak could mean "extreme backpressure"- meaning the exhaust gas isn't moving away from the engine fast enough to make room for new exhaust gas. (as in, the motor can't exhale). Or, fresh air could be getting sucked in, and running past your oxygen sensor... but that's usually with a y-pipe-to-catalytic-convertor leak- something close to the oxy sensor.

How bad is the manifold leak? Is it an inch wide, or a millimeter wide?

And yep, a fuel pressure gauge is a great investment. If my (or my parents or my friends) car ever acted up, and some "easy" things didn't fix it, I threw on the fuel pressure gauge. It eliminates one whole area of diagnosis pretty quickly. Plus, you can do an injector balance test with it, too. They usually sell the balance test as one unit, but you can make your own. The balance test is basically a fuel pressure gauge, a battery hookup, a pushbutton, and a stopwatch. The idea is to feed the fuel injector some fuel, and watch the gauge and stopwatch. After 10 seconds, the fuel pressure gauge will drop to a number. All fuel injectors should drop to the same (or very close) number after 10 seconds, or one is screwed up. You can do a "leaking injector" test with just the gauge, tho. I found my Sunpro gauge for $40 at Pep Boys a few years ago.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

manifold leak, as in passenger side exhaust manifold where it connects to the block. when i originally bought the car, two bolts were snapped and the used dealer i bought it from patched it up with some sealent, needles to say it wore out and the dealer fixed it for free. as for the size of the leak, i would think it is small. only when i get under the hood can i hear a slight ticking sound. it used to be real bad before it was fixed...could hear it all the time. but thats the extent of the history of my car...lol. yea, i hope its not the pump either, i can hear it turn on and stuff last time i checked for codes, but i think i am gonna try and by a fuel pressure guage, call it a hunch, but for some reason i think it might be that or the injectors....ugh!! just because it really feels to me like a cylinder or two fires when it feels like...i dunno....we'll see, but thanks for the help

[This message has been edited by SAEspinz80 (edited August 02, 2001).]

 

If it comes down to the exhaust, this might be some comforting news: I've had three sets of heads on my workbench; two were mine (one given to me, one I pulled off of a blown-up '87 Camaro's 2.8), and one was from my 2.8/2.8 swap friend. All had a snapped manifold bolt (or two!) on the head.

What's odd is, with vice grips, I was able to turn the snapped bolts out! It makes me wonder how the bolt head could've snapped, but the bolt itself turned so easily. Maybe the bolt head rusted to the manifold? Or maybe the shoulder of the bolt rusted to the manifold? Chances seem to be good if you pull off your manifold and there's a piece of manifold bolt sticking out of the head, you can nab it with vice-grips.

I wanted to do that on my 2.8 (if you look down for my "did some exhaust manifold porting" message) when I yanked the driver's side manifold. I noticed that the frontmost upper bolt was snapped. Unfortunately, when I had the manifold out, the bolt was snapped even with the head- and I wasn't about to try drilling it out with the head on the car. Besides, I don't have a tap & die set yet... I really need to get one, but I can't seem to find a complete set by a "good" name. I kinda don't count the JC Whitney sets...


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

yea i remember reading that post on the porting of the manifold...but its already been fixed, when the dealer fixed it a while back he drilled them out and re-threaded them....

 

Oh, the bolt's fixed? Great! Maybe you just have a loose bolt down there! Torque spec is only 25 ft/lbs, but my driver's side "lower front" bolt was so loose I unscrewed it with my hand.


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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

alright, i have been doing some diagnosis and think i have come to the root of the problem. first thing i did was re-check the resistance on my MSD wires, and they were perfect ranging from 79 - 90 ohms. then i used my multimeter on my MSD coil and it checked out fine too. the timing was at 12* and didn't fluctuate. and i also checked my TPS and got readings at idle of .69 and at WOT of 4.5. so the idle was a tad high, but probably not causing my problem from what i have been reading about TPS voltage. so i went out and bought a fuel pressure guage and got a reading of 42psi at the "on" position and about 36psi with the engine running....with in the stock numbers. so i was reading my chiltons and found another way to test the ignition. i started the engine and thnen unplugged the IAC sensor. then, it said to unplug on plug at a time and see if the rpms go down, if they don't you found a problem cylinder. so i did and as i was going i would check to make sure the spark was jumping out the the boot too. the when i got to the number 3 cylinder i got a nice shock. woohoo!!! turns out, the boot of my plug wire on the #3 cylinder is really cracked and beat up, it was evidently touching something it shouldn't have been. so i layed it ontop of the plenum behind the throttle body and watched the spark shoot out the sides. hmmmmm, not good. so i pluged it back in and watched it and sure enough the spark was jumping to the alternator bracket. so i don't think it was ever getting to the plug...explaining the hesitation. so i just wanted to supply an update for everyone, my parents are mailing me my extra MSD stuff, luckily i bought a V8 set so i would have extras. i will let you know the results, but i think i definately pinnned it. like we said....SOMETHING STUPID....lol, thanks for the help

 

yup!! runs like a charm....thank god thats over...