Hi All,
New to the forum here, spent some time scrolling through and couldn't find a thread that matched the issue I am having.

I have a 1991 Firebird Trans-Am GTA. 5.0 TPI. I bought it from the original owner, he had some issues with it and parked it a few years ago. I picked it up this past winter, he said it would not start, he tried to diagnose it but isn't good with cars and took it to a local shop. The shop said that it probably needs a new fuel pump.

Brought it home and finally had some time to work on it over this weekend. It cranks well, no kick or trying to start. I can hear the fuel pump running so I decided to spray some fuel in the intake right at the manifold. It started pretty quick and idled on its own. I let it run for a bit, moved it around the yard and seems all was well. So we took it down the road, I was easy on the gas for the first 5mins. Once I started to get into the throttle it started to struggle and wouldn't go above 3000rpm. Brought it back shut it off and if I let it sit for more then 10mins or so it wont restart without a shot of gas in the intake.

I believe it to be a fueling problem since once it gets gas it starts and idles. But underload it breaks up and at idle it surges. I tested the fuel pressure, at the rail schrader valve I have 40-45PSI with the key on and primed. Running at idle it sits between 35-40PSI. I put it in gear and put a load on it and the fuel pressure didn't change. Also the gas looks clean and clear coming out of the rail, I put some fresh gas it in before hand. Next I tested the fuel injectors resistance (ohms) thinking the injectors are the issue. Drivers side (ohms): 6.4, 25, 27, and 6. Passenger side (ohms): 13.2, 11.5, 17, 12. Based on what I read at least 4 of these are not performing well (anything 12 ohms and under).

As its some work to get to the fuel rails I was going to replace all 8 with remans. Before I commit to purchasing all 8 I was hoping to test the waters on here and see if that makes sense. I am also going to replace all spark plugs, wires, distributer cap & rotor, coil, and air filter as I normally do with a new to me car.

Do you think I'm on the right path? Any suggestions I haven't noted? Appreciate everyone's help!

 

Injectors get sticky after sitting. I would pull them and have them assessed/cleaned. Any injector shop can deal with this. It's a common issue w cars that sit and don't have fuel stabilizer. I had it happen on almost new injectors after sitting for 2.5 yrs.

That said, replacing them may be the move but is is necessary? One could argue to just replace because of their age.

 

Thanks Firechicken. I just did some googling and looked into local shops for cleaning/testing and unfortunately, their cost to do a full service is about the same as getting remanufactured injectors. I'm glad you are thinking the same, injectors as being the issue. Hopefully this is the case. Not sure what else it could be, I think I ruled out everything else. Let me know if theres something I missed.

 

Just get a good set from SouthBay Fuel Injection. They'll take care of you.

While you wait for them to arrive, go ahead and do the basic tune up you were planning on doing (plugs, wires, cap & rotor, air & fuel filters, oil & filter change, tranny fluid & filter, maybe even the diff fluid, etc.). A good tune up and new injectors will either make a big difference, or at least get you moving in the right direction.

 

Didn't they install those multech injectors from I think 89-92? Those are the grayish green looking things... the internal coils short out in them.


Id dump those injectors and get the delphi units from south bay. they look almost exactly like the multechs but are black and have a better internal design.....They are pricey but that's probably the best stuff you can get for these cars.

 

Currently my injectors are that grey colour.

Ill take a look at their website and see if they have what I'm looking for. Do you guys know what the stock injector lb/hr rating is? I see a lot of difference in injectors and want to make sure I get the right ones without needing to re-tune the car.

 

https://www.southbayfuelinjectors.co...d-305-tpi.html

The 1989 to 1992 LB9 5.0L TPI engine used 19 lb/hr Rochester Products "Multec" injectors. All 89/92 RP Multec injectors are bad LB9, L98, LT5, LT1. No matter how they test or run. Ticking timebombs. Russian Roulette. Not a matter of "If" just a matter of "When". Never troubleshoot any running or drivability problems until they have all been replaced. They will fail in ways that make you chase your tail around in circles like a dog. They will test good and be bad. They will fail intermittently. They must GO!!!

The brand new 19 lb/hr Delphi injectors are what you want for a 100% bolt in and go, no adapters, no tuning solution. On a perfectly running 100% bone stock engine they run 105% better than perfectly working RP Multec injectors ever did.

They also run quiet. Not the Tick, Tick, Tick, Tick you get with the other rebuilt injectors. TPI is "Batch Fire". If 1 injector is firing then all 8 of them are firing at the same time. The RP Multec / Delphi injector replacements are quiet by design. The used rebuilt Bosch replacement injectors were mainly used on engines with "Sequential Fuel Injection" that fired the injectors 1 at a time in order and not "Bank Fire" or "Batch Fire". They weren't noisy on the engines they were intended for. You fire 8 of them at once you going to hear them ticking.

The new Delphi injectors also look right on a TPI engine because they have a similar style/design as the factory RP Multec injectors.

 

Yeah, those are the multec... Id dump those. and go with the delpih IMO

Others like the Bosch 3s or something but people say t causes drivability issues / you need a tune etc...

 

Hard to ignore the price of those Delphi injectors. Especially considering I live in Canada and our dollar is crap. Roughly $700 Canadian delivered.

What do you guys think about the Bosch Gen II from SouthBay? Do they have drivability issues like then 3's? They are muchless expensive.

Before posting on here I was going to get remans from Rockauto but I assume these are just rebuilt Multec's? Has anyone had luck with remans or are they just the same and will die after a short while?
https://www.rockauto.com/en/moreinfo...6224&jsn=21251

I don't want to do this job again in a few years but also don't want to spend close to a grand. Hopefully there is something in the middle? Appreciate the help.

 

I don't like spending money. I don't. It irritates me. Spending $700 for injectors would irritate me, and I wouldn't want to do it. I was confronted with this exact issue, ~6 years ago when I was resurrecting a 'Vette that had sat for ~5 years. It had Multec injectors, they ohmed all over the place (similar readings to yours), and 5 of them were plugged. The "proper" thing to do was to buy new or re-man'd but I didn't want to. So? I found another make/model/engine that used the same pph injector, I went to Pick 'n "Pull and bought 8 injectors from the right make/model/engine car(s). 6 BUCKS EACH. I paid my $48 went home, put 'em in, and went out and did this.


They worked. It was, perhaps, a temporary measure just to get the car going at that point in the project. Buuut, they worked so damn good that they're still in there. In fact, those same cheapy-cheap injectors recently made 289 RWHP, installed in a SuperRam on the same engine. So? 6 years later, that $48 bux was worth it. Probably not a popular option on these here forums, but a viable option.

 

I believe those are rebuilt multteccs for 89 plus that R/A sells. So they'll likely fail again. I had ,ultecs in another GM and they SUCKED.....


My understanding is that people need to do a tune with the bosch injectors and they may not ft properly etc... I think I recall seeing that you might need to purchase an adapter to prevent leaking??? But I have no experience with those..... some people seem to have no issue while others do from what i recall reading. thats one reason I went with the delphis...


But if all else fails ($700 is a LOT) you can buy some maybe used 5.0 TPI injectors from a TPI that's pre 89. Mine were fine but i was redoing everything and the O rings were brittle, so I decided to just get new / refresh things. but my original 87 injectors worked fine.. as I recall there are 2 types of older style injectors...I believe Lucas and some other type.. I think it is a bosch design (they look identical except for the tips)

SB also sells rebuilt older versions on ebay..it was enticing but I personally went with the delphi..... Try see what they have to offer.

If I recall, my research told me that the 5.0 dephis are actually made / specd for 90s .I think 2.2L 4 cylinder Sonomas and S-10s. Youd of course need to do research to confirm if you want to go that route.

 

I'm going to bite the bullet and order the new Delphi injectors. Sounds like its the best option. Does anyone know the exact product code for the 5.0L 19lb injectors? I can only find the part # for the 5.7L and want to do some price matching before I order. SB website doesn't note the # and I checked Delphi's website and they don't even list it.

 

Give SB a call. They'll help make sure you get exactly what you want.

 

They have it listed as "19lb 5.0 Camaro Firebird 305 TPI" and "22Lb Corvette Camaro Firebird 5.7 TP"I" they have other pressures as well but they all look the same so look carefully....
the 19Lb is listed as 4228

"The 19LB Camaro Firebird 5.0 TPI 1986-1992 features new replacement Delphi fuel injectors, optimized by SouthBay Fuel Injectors. These injectors are engineered to be compatible with a range of fuels, including those oxygenated with MTBE, serving as replacements for the GM-style Multec injectors. They offer a flow rate of 19.3 lb/hour or 200 cc/min at a GM pressure of 43.5 psi."


I forgot his name, but the owner is really cool and helpful. You might want to call and double check.


FYI, I believe the TGO discount code doesn't work on the delphi units... I talked to him and he said unfortunately the discount would cut the margins too thin so it doesnt apply to the delphis....that was a year ago though....very understandable though. Excellent product so no worries there. Change the FPR while you're in there... they sell those too.


You might not want to hear this.... but if you're gonna put these gems in Id consider getting a brand new fuel pump to replace the 30 something year old unit and cleaning out that old gas and start everything fresh. id even rebuild the fuel rail as they have the O- kit for that since it all has to come out. .02

 

Do you still need to replace the original Multecs if they were running good before the car sat? The fuel lines and gas tank were purged before I stored the car. When I ohmed them, they all were within spec.

 

Everyone has their opinion and I have a very strong opinion about 89 to 92 RP Multec injectors. Everyone is entitled to their opinion and they own their car and can do whatever they want with it.

Do you actually drive your car or just look at it in the garage?

If you do drive it is it more than around the block to warm it up and put gas in it?

If you just look at it and take it for a trip around the block and gas it up and maybe go a few miles to Cars & Coffee you probably can get away leaving the RP Multec ticking timebomb injectors in it. Only run pure gas E00, never use any fuel treatment or additives that aren't GM approved for use with the RP Multecs, never use HEET or anything like it. The only thing that should go into your gas tank is pure ethanol free gas.

If you actually want to drive your Trans Am GTA as a normal car sometimes then Hell no you can't leave them in there. My opinion.

8 grenades with the pins pulled and a rubber band wrapped around the handle under the hood baking in the heat. It only takes 1 rubber band snapping to ruin your day. If you can live with that then you are good to go. You pay the price now or you pay the price later on. But sooner or later you will pay the price. Pay it on your terms or pay it on the rubber band's terms. In your garage on your terms or 250 miles into the road trip you took your wife on.

 

I know that Multecs have problems....I've had some that had problems (See my post above). But I also don't like to, or agree with, arbitrarily replacing stuff that works. Everything in the car will fail...someday. Should we replace everything, today? No.

To that end, my '92 has Multecs. It has ~215,000 miles on and I DD every summer. I expect the injectors to fail at some point...I've expected them to fail, for years. One day, one of them will fail, and I'll replace 'em. But in the mean time, I've had tens of thousands of miles over the past 15 years of ownership, of perfectly fine service from those "8 hand grenades" . I'm perfectly happy that I've NOT spent money on injectors, that so far, I haven't needed. Car runs great, so what's the problem? Some day, they'll fail. That day, I'll drive home on 7 cylinders and change 'em then. NBD.

 

Thanks Tom!

It gets old when everyone jumps on the same bandwagon saying to replace them even if they ohm to spec and have been operating well before storage or before pulling the car apart. I appreciate your sentiments. I agree. Everything will eventually need to be replaced someday so why prematurely do it if you don’t have to.

I think it’s probably the mod mentality of some people around here who want better than factory stuff. I can understand that. However, if you’re on a budget or going after a restoration using OEM parts, I don’t see why keeping the Multecs (if they ran good and ohm to spec) is such a bad thing. In some ways, it’s like arguing whether or not to keep the original TPI because it choked the 350 at high rpms.

When my car was on the road, I had no problems with mine. On the other hand, my uncle had a problem with one of his right after he bought his ‘91 Z28. Luckily, the used car dealer fixed it under warranty. I remember that day clearly standing on the lot anxiously waiting for the mechanic to replace the injector so we could take the car. It felt like he was taking forever. I guess they didn’t want to increase their costs by getting new gaskets for the plenum so they had him R&R the injector with the intake still on the car. After what seemed like an eternity, he finally got done. Yeah, he did it right there on the lot. When we got the car back, it ran great afterwards. No problems with the rest of the Multecs after that.

 

I did drive it before I took it apart.

When I drove it, I would typically travel 10-20 miles per round trip with some averaging 30-40 miles. It never was a daily driver, though. I probably used it maybe 2-3 times a week.

I don’t like looking at it in its current condition. It’s all pulled apart up on jack stands. However, when I get it back together, I will definitely stare at it for a couple of months while driving it on short trips in between. Traffic/population around here has increased tremendously since I first bought my GTA so it will never be a daily driver. I’ll probably drive it even less than when I first got it.

Well, I think I’ll keep the Multecs because they are original to the car and they never gave me any problems when the car was running. It only has 76k miles on it so I think they should be fine. If I start to replace things out of fear on what could go wrong, I’lI be replacing everything. Might as well get a new car. I remember when these cars were new. I remember sitting in them in the showroom and also test driving them if I got the chance. So, I guess it’s nostalgia related on how I want to do things. I want to keep as many things original to the car and only replace the stuff that really needs it.

 

if they run well, keep them.

They'll probably crap out eventually but unil then run them until they die / you get issues. . o sense doing all that work / money if its stil lgood.

 

Closing out this chain in case anyone comes looking for the solution,

First off, thank you to everyone who replied. The group is super helpful on this forum!

Ahead of this weekend while I was waiting on the injectors to arrive I did a full tune up on the car. New spark plugs, plug wires, distributer cap, distributer rotor, ignition coil, fuel filter, and a engine oil change.

This past weekend I changed all 8 fuel injectors with the new Delphi units from South Bay. Not a easy task, however it "only" took 1 8hr day. I was expecting 2 days at least. Before I started taking everything apart I did what I'm sure we all do, jump on youtube first and see if I could find a video to get some tips. In the one I found, the guy took the intake runners completely off to allow the entire fuel rail to come out of the car. This was my plan until I realized i needed some better wobble T40 sockets for the bolts at the bottom of the runners. To save time and having to wait to find a good set of wobble sockets, I found that if you take off the plenum you can loosen the 4 fuel rail bolts and disconnect the fuel feed lines at the front of the engine. This will allow the rail to raise and pop each injector out without removing the full rail. Keep in mind there are clips on the original injectors that you need to un-lock before you can pop them out. These also arent used on the new delphi units FYI.

Then I worked on getting the new injectors in. Put them into the intake manifold first as they are slightly shorter, then put the rail on and tighten them down. Before you move on to the next step, prime the fuel system by turning the key to ON and back to OFF a few times to get the fuel up to the injectors to check for leaks. I also threw on my fuel pressure gauge to ensure they did come up to 40PSI and didnt leak down. Be careful to not damage any of the O rings, I cut 2 of them during install and had to take them back out and replace. Don't be afraid to take off more items then you think you need, it helps as the engine bay is very tight, I moved the alternator out of the way, the top radiator hose off the engine. Both of these helped getting the fuel feed lines off the rail.

Long story short. The car runs amazing. Took it down the road and it rev'd up fantasic, power is back all the way to redline. The injectors are also super quiet compared to the stock units. What everyone on here said is true, its worth spending a few extra $$ to have it run amazing out of the box.

Unfortunately the front driver side brake caliper seized up so I couldn't fully enjoy the car this weekend, but I have them on order so I can swap and take full advantage of next weekend. Also going to replace the trans and diff fluid while I'm at it. Along with some steering components that are a bit loose.

Thanks again for all the help.

 

Awesome follow up story!! LOVE it!

Sounds like the car needs more PM, which you're planning (good), but do the brake fluid while you're doing the caliper, then coolant too, so you're not posting about another seized caliper and a heater core soon.

 

100% the brake fluid will be changed out when I do the calipers.

Good point about the coolant. Are there any bleed points when refilling to get all the air out? I have a KTM dirt bike and that thing has multiple screws you take out as you fill it up with coolant to bleed the air.

I know this is a touchy subject, but what do you think about changing the trans fluid & filter? Tons of people are either for or against changing the fluid. I don't know when the last time it was changed. Its not perfect bright red but doesn't smell burnt and it shifts well. Car has 220,000kms/136,000miles on it.

 

I knew you would like those injectors after you got them installed. The price is a bitter pill to swallow at first and even worse if in Canada having to order them from the States but I think the Delphi injectors are worth it.

I wanted to wash my Firebird the other day because we were going to have 1 very nice cool low humidity day in the middle of a wave of hot AF Hell. Well on the way from the shop to the house the front brakes decided they wasn't in the mood for the car being cleaned up and put up one Hell of a fight. I had to downshift to Low 1 and use all the foot pounds of torque to make it. MFer was smoking hot when I got in my driveway. I mean it took all she had. 100% WOT in Low 1. I wasn't stopping because it would have never moved again from a stop. Was already sometimes lighting up the back tires while moving. I was real close to home anyways because my shop not far away.

She got her bath all shinning and new looking again. After sitting over night I can move her some but the front brakes groaning. Got me a stack of brake stuff from NAPA.

Man I wished you lived closer I would have helped you. Got all the tools that make it easier and the tips and tricks of doing it many times. Also have a 1991 Trans Am GTA parts car. 5.0L TPI 700R4 T-tops Brilliant Red Metallic with Beechwood Tan leather interior. GEM Mint 9.9 out of 10 dash pad and GEM Mint 9.9 out of 10 taillights lens. Lots of good parts. I'm doing her like the Native Americans did the buffalo. Nothing going to waste. Many of her parts living on in other 3rd gens.

 

Glad to hear!

"These also arent used on the new delphi units FYI"

Not sure about that though.. I removed the clips and transferred them over. the 4 bolts which I think are torqued to 25-35 ft lbs hold the injectors in place, but the clips are extra insurance.

be sure to check for fuel leaks around the fuel rail joints (not at the injectors but at the corners of the rail) .. I would have preferred to have replaced all of those but I know people don;t, but i have had them leak a bit after handling the fuel rail as the o rings get old.

 

DUDE.... I was waiting for this story to get worse! A guy on the 'Vette forum posted about a VERY similar episode he'd had with his wife's Corvette, it was identical to your story....but ended way worse. Body damage...fire ensued! I tried to search and find the post to share it w/you b/c it was hilarious, and mind blowing....and so similar to you story. MAN...I wish I could find it!

 

I transferred the clips to the new injectors but they didn't line up with the location on the rail. The rails are bottomed out and the bolts are tight. No Leaks at the joints in the rails or at the injectors. I thought it was odd the clips didnt line up but it was fully seated in the intake so i assumed it wasnt needed. Runs great and dosent leak.

 

thats dd, I have the delphis as wel land the clips fit no problem.

Save them clips just in case, i heard they are hard to find!

 

The clips fit perfect on the Delphi injectors. Got a box of used clips and junk RP Multecs. Not hard to come by I got bags of new ones. I'll post a link.

GP Sorensen 800-9411 Retainer Clip

You talking about those fuel injector retaining clips?

They all over eBay in bags of different amounts.

 

Thats the one!

Back in 2000 or so when I needed them for my V6 they were impossible to find / apparently nobody made them. That or the parts guys i used suck....But looks like thy are widely available now!

thx!