HELP PLEASE: Under high acceleration, at around 4-4.5k RPMs my wife's baby feels like it's "stalling". She feels as though she's not breathing well or possibly not getting enough fuel.
Backround - My wife's 88 GT had a 3.1 swapped into her about 24k miles ago. They guy who did it didn't do the best job of getting the top end (intake etc) back on and needless to say all the upper seals had to be replaced due to a vacuum leak.
That coupled with the $1200 in exhaust/cat and EGR work to get her running smoothly didn't make me very happy.
Bottom line, she runs great now, idles perfect, and drives like a dream with the exception of a power loss under the above conditions.
Any idea what a sudden loss off power or "stalling" sensation would be caused by?
THANKS a million in advance.

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"The last 29 days of the month are the hardest" - Nikola Tesla

Sounds like the point where power peaks and falls off on our engines. Or would you describe it more as a sudden loss of power like the engine shutting off? You could be going very lean from lack of fuel if the fuel filter was clogged or the pump can't keep up.

I suppose it feels like I lose power. It really does feel like she's not getting enough ______ into the cylinder. Fuel filter/pump would make sense as the chassis has over 225k miles on it and I don't know if it has ever had those replaced.
OR it could just be that I'm used to high revving engines. I haven't had a Fiero for over 2 years now. She pulls just fine at low RPM's but get it above 4k and that's it.
Any ideas? Thanks.

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"The last 29 days of the month are the hardest" - Nikola Tesla

My guess is that the lack of much power above 4000 or 4500 RPM is attributable to what Hudini first mentioned:

quote Originally posted by Hudini: Sounds like the point where power peaks and falls off on our engines.

With 225,000 miles on the chassis, a new fuel filter and fuel pump could be good insurance, especially if you're not familiar with the repair history of the car. However, even with those replaced, I'd think you still wouldn't feel much power above 4000 to 4500 RPM anyway because of the restrictive stock Fiero V6 intake manifold.

If you want more power at that RPM and beyond, a Trueleo intake manifold would be a good start ( http://www.trueleo.com ). I haven't seen one for a pushrod 2.8L or 3.1L engine, but here's a dyno chart nicely illustrating the difference one of those can make on a pushrod 3.4L engine:

quote Originally posted by Raydar on page 18 of the thread, "hi-flo manifold update": Here it is. (Thanks to Capt_Fiero for converting the image.)

In the above chart, look at the difference in horsepower between the stock Fiero intake manifold versus the Trueleo intake manifold over much of the RPM range, and in particular, above 5500 RPM. (Hopefully, somebody can post some dyno results for a Trueleo intake on a 2.8L or 3.1L engine as well.)

By the way, vertigo1, welcome to Pennock's Fiero Forum!

Thank you for the welcome! I've been browsing the forums for years and finally decided to contribute/join in.
Thank you for the suggestions.
I looked through the repair logs of the previous owner and it does indeed say that he had changed the pump back in '04.
However now I have a NEW problem that I believe is related:
I added a grounding strap as everyone is saying to do and it did indeed help with the electrical system (lights brighter, windows faster, etc) but now for some reason my idle is slightly off by about 300RPM - was at 800, now 1100. I made doubly certain that all the vacuum hoses were re-attached and all cables perfect before starting her again.
Also, when I accelerate relatively hard the car hesitates even at low RPMs - again like it's not getting enough ______.
Any suggestions on my new predicament?
Thanks a million.

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"The last 29 days of the month are the hardest" - Nikola Tesla

[This message has been edited by vertigo1 (edited 04-20-2008).]

Just for kicks, try resetting the ECM.

quote Originally posted by Blacktree: Just for kicks, try resetting the ECM.

Pardon my ignorance, but how does one do that?
Thanks.

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"The last 29 days of the month are the hardest" - Nikola Tesla

Again, let me re-iterate my ignorance - How do I go about resetting an ECM?
Thanks.

Just remove power by disconnecting the battery. I'm guessing Blacktree was suggesting erasing all the learned fuel trims so that the ECM can quickly relearn new settings with the restored ground. I've learned that the ECM looks at (among many things) the voltage to the fuel pump. Using that voltage, it has a correction factor it adds/subtracts to all your numbers. Could be it simply needs to start from scratch again?

Welcome to the Forum!

few guesses:
ignition coil
bad dist cap/rotor
bad valve spring

If the filter is 4 years old replace it and run a bottle of injector cleaner like techron through it. One tank of bad gas could restrict it.

While the stock intakes are restrictive at high rpm they can still reach 6k plus fine without feeling like they are stalling. Mine stays between 4k and 6500 almost the whole time its running with a stock intake. If I had the option I would like a better intake as they are better, but I doubt that is the problem here.

quote Originally posted by SCCAFiero: If the filter is 4 years old replace it and run a bottle of injector cleaner like techron through it. One tank of bad gas could restrict it. While the stock intakes are restrictive at high rpm they can still reach 6k plus fine without feeling like they are stalling. Mine stays between 4k and 6500 almost the whole time its running with a stock intake. If I had the option I would like a better intake as they are better, but I doubt that is the problem here.

Your Air/Fuel ratio above 4.5 with a stock into gets very rich to the point where most widebands stop reading it! To take a pure stock engine to 6k is almost pointless since you have long since passed peek power and youre not getting much HP back for the strees you're putting on the engine. 5k is high enough to up shift.

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[IMG]



Trueleo.com/fiero.htm
RSpiderII@aol.com

quote Originally posted by Francis T: 5k is high enough to up shift.

I am not knocking your product Francis. In fact, I did state I would like to have a better intake.... if my rule book allowed for it.

5k may be enough for a street car, but then again 2500, 3500 or whatever you want is high enough as well. Peak torque is usually made at a lower RPM than peak HP. Torque and HP are two differant animals, as you know. etc etc.

For me and my Fiero. Shifting takes time, seconds that could otherwise be used for accelerating. Especially shifting into the next higher gear for a few hundred feet before maximum braking for the next turn. Not to mention the fact you can not shift in a turn if you are on the edge of control. I just increased my rear tire aspect ratio from a 45 to a 50 series tire in hopes to gain a few more rpm/mph before blowing up to make it to the end of the front stretch at Moroso without shifting into 5th. Currently, I have to shift out of 4th around 6300rpm or 115 to 120 mph. Shifting at 5000 rpm would get me a top speed of around 80 +/-. Not to mention, Shifting into overdrive (5th) on a race car is like setting the cruise control. The Fiero is slow enough as it is in my class.

All I am saying is that the intake restrictions are nothing like what the poster is describing and it would be unjust to have him spend hundreds of dollars on parts when he may have a dirty $5 filter. I do not have any stalling like symptons on my car at high rpm, but more power would be a good thing. My car will be idling at 2500 to 3000RPM after a 20 minute session on the track because the ecu is programmed to make adjustments for the way the vehicle is driven even in excess of 5k where it spends the most time.

Could be he does have other probs and I was just talking in general terms about 5K being high enough. If you look at that dyno sheet you will see 6k is also way passed peak tq. And yes you shift beyound your peak in a race to make up for the drop off, but 6,5K is realy pashing it. With our intake my other mods I tended to take it to 7k so often I had my son burn me a new chip for a 6.5k rev limit not wanting the added stress on the engine. When I use to race Mopars I shifted just lil beyond peak. Once you can feel the power dropping I dont see the need to keep pushing it. BTW: I did not respond to sell intakes, lots of folks like a the pure stock look and was aiming this respose at them. I just wanted to say 6.5k is just not worth it wioth a stock engine. And if you shift often above 4.5k your gas millage will suck, the engine is running rich.

If you are running the stock '88 ECM the following doesn't apply, but the earlier V6 ECMs did have a "soft" rev limit value that could cause the high-RPM symptoms you describe.

The fuel filter is cheap and easy to change, so that would be a good place to start. It wouldn't hurt to attach a fuel pressure gauge and see what's actually happening there when the problem appears. If an ECM rev limit isn't involved and the fuel pressure is OK, then the problem is most likely ignition related.

Finally, a 3.1 using the stock 2.8 injectors and stock ECM will run slightly lean due to the higher engine displacement. This usually isn't a big problem, because the O2 sensor conveys that information to the ECM, which responds by increasing the BLMs to compensate. The problem is that the ECM drops back into open-loop mode at full throttle and high RPMs, so the engine may be running lean there. I have never noticed this in my '88 with a 3.1, but I don't spend much time above 4000 RPM, either.

[This message has been edited by Marvin McInnis (edited 04-23-2008).]

I had a similar problem once in my 2.8. Started at around 5.5K and over time it wouldn't rev over 4k. Problem was some cam lobes went south. If cam break-in was not properly done that could be a posibility.