FI or carb???

OK. I'm way confused. My '91 Calais appears to have a carb, but all the manuals and online sources for parts say the 2.5L engine is TBI...which is throttle body injected.
The reason I thought it was carbed is that it has the round air cleaner on top and when I pull off the cover I can see the throttle blade.
Am I screwy thinking this is a carb?
If it is TBI, does that mean it has only one injector mounted in the throttle body (I seem to recall reading somewhere that that is what TBI means) rather than one injector for each cylinder?

Thanks!
Thomas

OK. I'm way confused. My '91 Calais appears to have a carb, but all the manuals and online sources for parts say the 2.5L engine is TBI...which is throttle body injected.
The reason I thought it was carbed is that it has the round air cleaner on top and when I pull off the cover I can see the throttle blade.
Am I screwy thinking this is a carb?
If it is TBI, does that mean it has only one injector mounted in the throttle body (I seem to recall reading somewhere that that is what TBI means) rather than one injector for each cylinder?

Thanks!
Thomas
It is TBI one injector for all 4.

Throttle body injection came along on most cars long before the port fuel injection except on high performance cars. The throttle body injection system looks like a carb. If you remove the air cleaner and look at the opening to the carb you will see a small round injector sitting in the center of the bore. It is possible that it has two. When the car starts the throttle plates open just like a carb to allow air into the engine. The injector sends fuel into the engine through the opening as well and the engine runs. Your car does have throttle body injection.

Throttle body injection came along on most cars long before the port fuel injection except on high performance cars. The throttle body injection system looks like a carb. If you remove the air cleaner and look at the opening to the carb you will see a small round injector sitting in the center of the bore. It is possible that it has two. When the car starts the throttle plates open just like a carb to allow air into the engine. The injector sends fuel into the engine through the opening as well and the engine runs. Your car does have throttle body injection.
Wowsers! Many thanks for the answer.
I looked at it, as you said, and then found that Autozone has good repair info on their site including drawings. It is, indeed, one injector. That's so bizarre.
I guess I'm a bit spoiled, being used to the Bosch mechanical and EFI injection systems in my volvo and my rabbit convertible...I expect one injector per cylinder...now I feel really stupid.
And thanks for the advice on the backfire...I'll do the compression test. A buddy said to change the fuel filter as it sounds like "lean backfire" to him and he thinks low fuel pressure...so I'll be checking that as well...he also suggested the Crank position sensor. And I'm going to check for vacuum leaks...now that I know it's FI I understand a whole lot better what's going on inside.
Next step after that is to take it to the mech and pay for diagnostics, I think...how hard is it to replace burned valves?
It's just so frustrating because everything I try doesn't matter...the car doesn't act up until it's under a load, so sitting at idle where I can run tests doesn't help...even when I rev it with the AC going...it still won't backfire.
Thanks again!
Thomas

If you find that you have burnt valves you will have to remove the head from the engine and take it to a machine shop. While you have the head off you might as well have it cleaned, new valve seats, if they are bad, if not have a valve job done. Of course you could purchase another one, if you can find one, these heads are getting hard to find a new head would be expensive.

If you find that you have burnt valves you will have to remove the head from the engine and take it to a machine shop. While you have the head off you might as well have it cleaned, new valve seats, if they are bad, if not have a valve job done. Of course you could purchase another one, if you can find one, these heads are getting hard to find a new head would be expensive.

Ah...Sorry...I should have been more clear. I have pulled heads off of many cars and done valve jobs. I was sort of wondering how difficult pulling the head is...it doesn't look any harder than a typical 4 cylinder. Is there any special magic or tools required?
I would much rather it be a burned valve than a bad fuel pump...because no way I want to pull out the fuel tank. How stupid is that? All the Rabbits and Volvos I've owned have an access hole under the back seat...this is unbelievable...
How hard is it to make an access hole inside the trunk to get to the fuel pump?
Thomas

No special tools are necessary to remove the head but use new head bolts when you replace it. Also be very careful to use the proper torque sequence. The 2.5 had some odd torque readings. Also the torque pattern listed on the Autozone website is incorrect so consult a service manual for the correct pattern.

I just went thru a head change on my dad's 2.5 (89 Cutlass Ciera), was much easier than I thought it would be. Easier if you block up motor and unhook front engine mount, and drop car down a bit to force motor frontwards a bit. Makes it easier to deal with. The head bolts are a bit of a pain as they are based on torque and then additional turning of the bolts, instead of a final torque figure. One bolt does not get tightned as much as others since it is in water jacket... Hopefully you won't have to do this though. Don't know what issues you are having but we had to replace ignition module and crank sensor a while back on this car as it had running issues, especially when damp. If you go ahead with a head removal might I suggest you go ahead and replace the lifter cover gasket as it is right there after you remove the intake/head. Hard to fix later if it starts leaking and is cheap insurance. Ditto on oil sender unit, as we just had to go back in anf replace it as it started leaking weeks later on us. One other thing, the crank sensor on a 2.5 in UNDER the ignition module. Maybe check that for cracks too, and get module tested as you have to remove as a unit, crank sensor is several inches long and sits inside block. Hope some of this helps a bit.

Thanks! Very good info!
Thomas

just replace your fuel pump. If your wondering, try doing a fuel pressure test first. Also, to check your pressure regulator, pinch off the return line if possible. A fuel filter is easy to change, but I suspect your fuel pump is running at about 30%.

just replace your fuel pump. If your wondering, try doing a fuel pressure test first. Also, to check your pressure regulator, pinch off the return line if possible. A fuel filter is easy to change, but I suspect your fuel pump is running at about 30%.
Huh? "Just replace the fuel pump"??? You make it sound so easy. Have you tried doing that on these cars? It will cost me more $ to replace that pump than I paid for the car. I'm not going to replace the fuel pump until I know it's bad.
Can you tell me how pinching the return line checks my pressure regulator? Simply saying "pinch the return line if possible" doesn't help. What should it do when I pinch the return line? What should it not do?
At any rate, as I've said before...the problem turned out to be a cracked spark plug on the #2 cylinder.:banghead:
Thanks to all for the help!
Thomas