91 TransAm GTA, 350 tpi, 114,000. I try to do as much as possible myself but I'm still a newbie.

It's been gradually losing power since I bought it a year ago, at first not noticeable. I thought it was associated with getting hot, because when it was hot it would lose power and sound airy, kind of like in neutral, but never *really* obvious, couldn't nail it down.

In order of what has happened : (about 3 or 4 months ago the alternator died but this is not the problem because the alternator was a straightforward case, and clearly electical.)
The only mod is a welded flowmaster muffler, got it about 3 or 4 months ago, about the same time the alternator went bad. It gives me really great mileage and I am not eager to take it off, because I like it and I can't really believe it might be making my engine run lean... But the car really hasn't been the same, at least, it made the power loss more noticable.
It was barely kinda missing, I would have changed spark plugs *then*, but then the temps suddenly started going up. My mechanic suggested I have a dealer check the codes because it wouldn't be helped by spark plugs. That was a month ago. There were no codes but the dealer said power loss could be a fuel filter (he did that) and a thermostat would fix the temps. I should have had him check the fuel mixture then, but I didn't know any better. I put in a 180 stat which fixed the temps and the car should love the new lower temps but there was no effect on performance. In old times it used to really react better when it was at lower temps. It is missing more than ever now, and all the time, (not due to taking longer to warm up.) It's really missing badly while accelerating. Very jerky.
I bought an oxygen sensor but I haven't changed it because I don't think it will help and the old one looks good. I've also recently (3 days ago) had changed spark plugs & wires, thinking it was now obviously causing the missing, but it didn't change a thing. In fact I think they screwed it up even more, considering how hard they are to get to. But the old plugs weren't that old, and the wires had been ok.
If it isn't the exhaust I have some general feeling that it's the fuel injectors or maybe with the egr. I knew I should have bought an older car!
I've decided to take back to the dealer for a different diagnostic, or at least a diagnosis, because my mechanic is nice but not very helpful. At least at the dealer I get free snacks, but I hate spending that money and I'm frustrated with my ignorance! I have gotten really good advice from the message boards! All advice is welcome. Except what my mom said, which was "Why didn't you buy a cute little mustang?"

 

has the fuel pressure been checked ?

maybe its a bad fuel pump ...

 

Could be, fuel pump...seems everything has gone bad on it the past few months. I wouldn't say its surging, but it's almost like a bad mixture, when it's idling and it skips or misses, it really rocks the car. No backfiring, yet, but every day it's worse. I'm trying to get a grasp on this, since I don't know much about fixing it myself, I need to be careful.

 

Sorry about the extra post. I'm still a newbie.
In Re. to Z's R best: the possible blown head gasket (Can't even see my $#@# spark plugs, or I would have done them myself...) Well, I ran the car a bit, It's dark out and I couldn't see any arcing down there. I would hate to have a blown gasket but that would also explain the power loss. No check engine lights, at least it could give me a clue. There's no leaks or anything.

 

Thirdgen injectors are semi-known for shorting internally. You'd need an injector tester or an ohmmeter to test resistance of each one though.

 

My dad is convinced I got screwed with the tuneup, and that they probably left some wires loose or worse, because the misfiring has been really bad since then. With my limited experience I can't get to the spark plugs at all. He wants me to take the to his mechanic tomorrow, which means leaving it there all day and not getting any input from that guy! This is not going to be good. I can't really argue though because I'm mostly broke. How much does an ohmmeter run?

 

I got a cheap ohm meter from Radio Shack once for $12. Not the greatest thing in the world, but it does the job.

What kind of exhaust manifolds/headers do you have? If you have stock manifolds, you shouldn't have that much of a problem reaching on the side of the motor and takin' out the plugs. Just follow the wire down. If you have headers (ESPECIALLY Edelbrocks), they could be harder to get at, but with most good headers, you can get at them with even a socket/ratchet, so they are easy to get at.

Check the top of your distributor and make sure all the wires are down on that. If you hear a click when you push on them, then you know what's going on. Same for the other end of the wire. Follow the wire down with your hand and see if the wires pull off the plugs with the slightest tug. Also, check to see if the wires laid against your exhaust. They could be all fried inside. *** knows my old headers LOVED to eat plug wires because they hugged the plugs so closely (even with shorty plugs).

 

Where do u live? mabey someone here isclose to where u r. there r alot of helpfull members here.

 

GTA,

If the misfire is more apparent after the spark plug and wire change, that would be the first item to investigate. Remember that you want consitent plug gaps, "regular" spark plugs (not the designer plugs like SplitFires or Bosch +4), suppression wires with silicone jackets, and recheck the firing order closely.

You should also test fuel pressure to eliminate that potential variable.

The oxygen sensor change would also be a good idea, since they do degrade over time.

Be aware that the '90-92 cars used Multec fuel injectors, a type which is more prone to failure of the operating coils. That may not be your problem, but it is always a suspect.

Hang in there. We'll get you running yet, but we can't do it for you. You're going to have to get your hands in there.

 

Thanks, thanks! I am checking this all out right now. I didn't get fancy plugs or anything, not even bosch. I've seen what badly gapped plugs can do on my friends cars. My headers are still stock. The wires were good, all tight at both ends and not near to the exhaust, so they didn't get fried. It's possible the order got messed up, though. In my neighborhood where I live in California, everyone and their mother is a mechanic and nobody drives stock, but I'm finding out how if you want it done right you have to do it yourself.

 

Look closely at the #5 and #7 spark plug wires. Not only are they physically adjacent on the left head and distributor cap, but they are adjacent in the firing order. It's an easy mistake to make - I can say that having done it more than once myself.

 

Dum dum dummmm....
Well I just spent the morning at the mechanic (after waking up with a bad cold.) They ran a complete diagnostic. I got a look at the printout (hopefully I can keep it later) and the mechanic explained things to me. (which the dealer place was smart not to do - I bet the time I took it to the dealer they never even ran any diagnostic!) The diagnostic found problems in 7 of the 8 cylinders. Looking at those numbers, from what I could tell, they should have been like 500 or so and they were 70's and below. After berating me about mistreating my car, said (the other place) probably yes burnt the wires and they crossed wires which they shouldn't have. The diagnostic found trouble in the distributor but it might just be the spark plug problem, so that's not a concern (yet). The fuel injectors are either extremely dirty or completely screwed up, so I guess they will get cleaned, hopefully it will not be a worse problem. Other things that came up was possible vacuum leak (not doing anything about it yet), and I am still keeping my fingers crossed that it wasn't a blown head gasket because the diagnostic asked to look for arcing in the spark plugs. Also I learned my car is a gross polluter which was no big news, but I got to see the real numbers. It was running hydrocarbons of 500 at an idle and over 1000 at higher rpms. I also found that it was having a fuel rich mixture, so I can't blame the exhaust for the problems, which I had long suspected of making it run lean.
How did things get so bad? Well, I guess I *did* always want to know everything that was wrong with it.

 

Things go bad over time sort of like you said. At first you don't notice it because it's so gradual then when you do watch out. At least now you know where to get started. Good luck with your repairs. Are you still planning on doing as much as you can yourself?

 

GTA,

If you have misfire, the unburned fuel will turn your engine to a "gross polluter" in no time. That's why the HC readings are so high.

As for cleaning your injectors, forget about it. They are most likely Multec, and not even worth the trouble. If the mechanic doubts this, have him get on his AllData (they DO have a subscription, right?) and check the numerous TSBs on these injectors in GM engines. The final "fix" is to install a different type injector, as GM did a couple years after beginning to use the Multecs. You should be able to get a set of injectors from various sources and have them cleaned, tested, and installed. This may also not be something that needs to be done immediately, unless you have one that is leaking constantly or shorting and blowing one of the two injector fuses. If the fuel pressure will hold when the engine is turned off, the need for replacement injectors may not be so urgent. This would allow you time to acquire a set of injectors and have them properly serviced (ultrasonically cleamed and flow-matched) before installation.

Not to argue with your mechanic(s), but if the diagnostic was "complete", what were the results of the injector power balance test?

 

This is the bulletin on Multecs, however I have seen an injector flush cure a leaking Multec injector. The customer was faced with paying around $1300 for a new set....or he could spend $100 to clean them and see what happens. Well, we cleaned them and "problem solved". :shrug: You never know.........

Document ID # 250973
1991 Pontiac Firebird

--------------------------------------------------------------------------------

INFO ON MULTEC FUEL INJECTORS DO NOT CLEAN MULTEC INJECTORS #91-6-26 - (02/15/1991)
Subject: INFORMATION ON MULTEC FUEL INJECTORS/CLEANING

Models Affected: 1986-1991 ALL MODELS WITH PORT FUEL INJECTION

This bulletin has been written to inform technicians of possible damage to Multec injectors as a result of cleaning.

The ball and seat design of the Multec injector eliminates the need of ever having to use an injector cleaner. By design, the fuel metering portions of the injector are not directly exposed to the intake manifold gases that are responsible for the build-up of deposits that can cause injectors to clog. (see Figure 1).

Some of these cleaners may contain high percentages of alcohol and other solvents that cause damage to the injectors' coil wire insulation. Damaged insulation results in low resistance or shorted injectors. Also, alcohol reduces fuel lubricity which increases friction at the injectors' critical bearing surfaces which results in premature wear.

General Motors has conducted extensive injector cleaning studies to determine effectiveness. There is no confirmed evidence that cleaning Multec injectors has resolved a vehicle driveability problem. In addition, suppliers of various injector cleaners may claim that their product can also clean intake valve deposits. General Motors laboratory tests have shown that injector cleaners have little or no effect on intake valve deposits.

General Motors maintains the position that Multec injectors should not be cleaned.

Figure 1

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.

 

I guess the GM TSB doesn't mention the 12,000+ vehicles recalled through 1996 due to leaking/failed Multec injectors.

The Multecs don't even make a good paperweight, since they are too rounded on the ends. Don't even consider buying them as replacements. The alcohol in bottled injector cleaners have the same effect as alcohol additives in fuel (ethanol), but just a little faster. These things fail in the midwest like snow melting in May. Funny how the Bosch and Rochester/Lucas CAV injectors don't have that problem.

If your's are working, leave them alone until you can get good replacements. Just my opinion.

 

http://www.jegs.com/cgi-bin/ncommerc...14&prmenbr=361

$1300 for injectors???

 

Yes, injectors from GM plus labor at $72/hr = ~$1300.

 

That bulletin is from '91 so it probably wasn't updated or anything.

You know, here in CA we(my work at least) don't see Multecs go bad that often. What we do see is CPFI injectors sticking ALL THE TIME. GM issued a bulletin to clean CPFI injectors for free for 100K miles/10yrs, however this only applies to cars with YF5, the CA emissions RPO.

 

Well, I don't know whether the mechanic really cleaned the fuel injectors or not. Hopefully he didn't, after hearing that. They weren't really the problem anyway. At any rate, once the spark plugs were fixed, my hydrocarbons went back to normal, a little above 100 which is ok since I won't be doing a smog check until late next year. Phew! Everything is mostly back to normal. It just isn't fun unless its a crisis. Of course I still want to do as much myself as possible! If I can ever go a week without breaking something on the car...

 

Yeah, those remote poppets are a real friggin' treat, aren't they? They got so close to making the sequntial CFI into a real injection system that they might just as well have gone all the way. It can take half a day just to get the intake open to get to "them rotten little bastards" (as they were described to me).

The problems with the Multecs doesn't seem to be in the valve design (which is actually pretty clever, if not effective), but with the solenoid insulation. Anybody have a set of six 16-17 pounders for a '91 3.1 (NOT Multecs, thank you)? I'm still looking for some, since the set I checked has three out of six at less than 7 ohms, and one at 1.1 ohms (blowing fuses).