Ok, i'm new to this site, I just recently bought a 1991 305 RS with a TBI. I have delay problems with the throttle. It bogs down when you give it the gas, and then about a second later it goes. Any ideas as of what would cause this? I cleaned my TBI and changed my distributor and rotor and that still didn't help.

I already did a search on the site and didnt find anything.

 

My problem too.
I've been asking people for help for over 2 months now, and although they have suggestions it just does not seem to work.

I've replaced everything in the car, and its still doing hesitant like that.

All I can think of is fuel pump, but might not be it.

Damn, I''ll let you know how my troubleshooting goes.


I am thinking ECM problem...

 

My initial thought would be fuel pressure. If that tests at 12-13#, you may need to look into the throttle minimum air position. A nearly sealed throttle blade makes for some very still air in the bores.

 

Ok, I played with my TV cable today and actually set it right. Damn quite a difference. I knew I messed it up a bit when i changed the coil, but I didn't know I messed it up that much.

Now my hesitation has calmed down quite a bit, but there is still some in there. Now its betwee 20-30mph, and its fine if I accelerate through it. However if I were to brake and get down to that speed the car would, kinda, hesitate when given gas. I tryed different prom's and it was the same thing, so I narrowed down the problem to 3 things.
ECM, 02 (although I doubt that one) and fuel pump.
I will be changing those after I get paid on the 25th, so I'll let you guys know what happens.


The tbi hesitation is a very well known problem and its interminent so once I figure out what the hell was wrong with the car i will write up a guide for TBI dudes who have a problem.
Its a pain in the ***, especially when you are low on cash.

 

P.S. I am smoking tires again

 

Does the problem happen when the car is warm or cold? A bad 02 can cause boggin in an LO3 without any engine codes. It could also be fuel pressure as Vader suggests. What did you set your base timing too when you re-installed the distributor? Did you set it with the EST unpluged?

 

I am not sure what happened to the guy who started this post???
But timing is something he should check. I remember having my TBI -2# by mistake and it ran like crap. Now its around 4advance.
You really sure about the o2 shifty??? O2 is the only thing I can afford now so it wont hurt to replace it.

What about having a collector leak which is really close to the o2 sensor on the headers??

Anyway, my car does run good once in a while.

I will update this post whenever I replace anything.

Oh one question..

What causes the car to revv up on start up, even when its all warmed up???? LIke revv to 1700rpm and drop down.

 

Yes, an exhaust leak near the O² can dilute the gasses enough to create a lean indication, so the ECM would tend to enrich the mixture. However, leaks behind the sensor would have less of a tendency to affect it, and going rich may not be your problem. It sounds like you may be more lean.

 

New O2 is in and not much luck. Drove it for about 20mins. and it behaves the same, however I am noticing things that I haven't before.
Whenever the engine boggs down o2 would show very lean condition, and when I get on the pedal and downshift it picks up like crazy and goes to rich.
With every shift I go lean than rich. So shift to 2nd(lean) 2secs later (rich).??

Also when its downshifting it does the same thing just backwards, (lean) downshifts (rich) and goes down to (lean), than again.

My idleing in park is constant rich to lean lean to rich condition, and the car sounds like its missing a bit.

It very much so indicatates a bad pump.

However, i could not find a guage for fuel pressure today (checked at least 6 stores and called even more) Only one had a huge gauge that showed to 15psi (which would work) but it will take 4 days to get it, and its as big if not bigger than my speedometer.

 

This is all low end power, high end the pump stays ideal/rich when I get on it.

 

What would cause a high startup even when engine is warmed up. (really happening all the time). And than it drops to normal idleing?

Also, I went ahead and replaced my gas cap since it didn't want to screw all the way and would lock on first turn. This helped a lot too!
I wonder if there is not enough preassure in the tank for the pump!!!
When i drove it for about an hour today and took the cap off, there was very little to no hissing. Just very minimal.
Does that mean that the pump is going out, or that the preassure is escaping somewhere else.

 

Sorry for it takin a while to get back, but heres how it is for me. i haven't checked the o2 sensor or anything, im not too sure how to do it. this is my first car (im 16, just got it 2 months ago) and this seems to be pretty much the only problem with it. it has the delay when both warm and cold, and i also think theres something up with my idling. my tach is broke (doesn't help much) but when it idles it will get real low sometimes and sound like its normal, and have a nice low growl to it. after about 3 seconds it will go back up a little bit too. im just seeing if these 2 things could be related

 

I would change fuel pump and the ECM. Fuel pump because you might have to low of a preassure under load.
If you are going fine without giving it too much gas, than its probably the pump. Even if its not it would be worth it since its very old.
ECM (the computer) is acutally easy to replace since its two screws that hold it and than it comes down. Unplugg the connections and connect them to the new one. I really belive that a loose ground, or just bad connections can be fatal to the ECM. That are the only two things that I have not replaced and I am having the same problem.

I am really thinking the fuel pump and since you dont know how to do much (what am getting from ya, sorry if I am wrong) just hang on and see if you can get someone to help you. If not just pm me.

 

I wouldn't change anything just yet. Changing parts without diagnosis is not good a practice. You'll spend money and time on things that aren't necessary, and will still need to find the actual cause of the problem.

For the ECM, if the SES lamp on the dash does "the bounce" when the ignition is first turned on, it is probably working. If you can request a scan of error codes from the ECM (paper clip trick) and get it to display codes, it's probably working. If you can enter Field Service Mode (paper clip trick AFTER the engine is running) and get it to display mode, it is definitely working. Don't spend the time or money on replacing the ECM unless you need to.

We're already suspecting a fuel pressure problem, so until you can test the pressure and pump delivery rate (flow), there's no reason to continue changing parts. It's not a Mitsubishi Talon, where you can flip up the back seat and change the pump. There's a little more involved on our cars.

And even if you determine you have low fuel pressure, you need to diagnose further to isolate the problem to either the pump, filter, or pressure regulator. How about spending three days changing the pump, only to find that the pressure is still low, and all you needed to do was clean the seat of the regulator - Without ever having to raise the vehicle.

Buy, borrow, or rent a pressure gauge. It will make your life a lot easier. Even AutoZone has them. Actron CP7817, for both TBI and other EFI systems. They might even rent one.

 

Ya know, Vader is right! I did go replacing things and I replaced near everything and still nothing happened. I really had no access to the scaning equipment and could not find a preassure gauge for the fuel that I can use. So I went replacing everything and nothing helped. A lot of times from reading on the boards, since I did a lot of searching, most delays are either a bad pump or the ECM. Since I have not replaced those two things I highly belive they are the culprit. I also like carbed non-cc cars since they are a lot easier to adopt and modify (I really dont want to get into computer tunning).
So. I would suggest you do your tune up! and see if that fixes the problem. If not than do check all of your components.
Mine was so interminent that I could really not find what was wrong with it. Once I messed with my cap and rotor and got the car to run great. Than few hours later it started craping out on me again. So I replaced the distirbutor and all the sensors wires, even re-built the TBI and still the same problem. So, I was really thrown all over the place by my engine which could not tell me wether it was one part or the other than was not working. (no codes either).
Sometimes a good indication of something mechanical not working is if you are not getting a code. But here on the site, I got answers that a lot of things don't necessarily throw a code if they are bad. So off I go...

Anyways, sorry for the rant...
I'll reaplace my pump first, than if that does not work I will replace the ECM and I will make sure I'll let you know whats happened.
Laters.,

 

Ok, thanks everyone very much! and yeah, When i just lightly tap the gas its fine, and if i gradually go into the gas its fine. but if i try to put it to the floor even moderately slow, it will bog down. Thanks alot everyone and thanks WhellRaiser for your help too. and yeah, i don't know too much about cars yet, but gettin there.

 

Ya bud, I have the same problem. ANd I have been working on it for two months now. I have no access to much equipment nor do I have much money, so I am replacing a thing or two with every paycheck. IT kinda helps me feel better about my car having all the new parts.
Like I said it has boiled down to ECM or the PUMP. So I will be replacing the pump first and than if that does not work the ECM. I'll let you know what happens and I will send you few pics of how to change the pump. HOwever, I am doing an access door (which is all done right now) but I dont have enough money for the pump so gotta wait till 25th.

Laters.


Oh, and if you give it gradual gas you are putting less strain on your pump. SO, that right there tells you whats up.

I would recomend you adjust your TV cable. Go to tech articles here and find the TV cable adjustment. It might help a bit.

 

Have you checked for any vacuum leaks yet? Look at the PCV, brake booster, gaskets, all vacuum lines (and their routing and connections), EGR valve, and MAP sensor.

Did I miss something? A fuel pump is going to set you back about $100. A fuel pressure tester is going to be about half of that, probably less if you shop well. It may actually SAVE you $50 to get a pressure tester, not to mention all the work of changing the pump and hacking a hole in the floor of your car.

Have you even changed the fuel filter yet?

And even without a tester, you can check the fuel pump output volume. All you need is to remove the fuel line at the TBI, route it safely to a container, then operate the pump for 15 seconds. The pump should deliver at least one pint (16 ounces) of fuel in 15 seconds.

If the ECM is reporting as described, forget about that for now. Unless the PROM has been changed from stock, there's no need to look any farther.

 

I've been runing TBIchips.com stage 2 chip for almost a year now.
It had no problems what so ever, and it was a BIG improvement over the stock one!
I have quite a few things done to the motor though.
I am going for a cam next and really updating the pump.
However, my good friend swears that the fuel pumps either work or don't, and he keeps telling me not to worry about my fuel preassure. Since everything else is new in the ingntion (alt. has less than a year, batt has less than a years all new coil distributor MSD cap and rotor, MSD coil, new pluggs (AC delco) new wires, new sensors etc..)
It really feels like the car takes few seconds to pick itself up. It delaying the acceleration.
I would give it gas and than after I let go of the gas it would go.

Usually happens when I brake and get it down to about 20mph. I would give it gas and little to nothing would happen. Than I would press the throttle in 3/4 and nothing, than I would press it in a bit more and the car downshifts and picks up like crazy. ALl of a sudden when there is more demand on the pump there is plenty of gas. Its the only reason I doubted the pump from the get go. Why in the hell would I have no power on the low end but have plenty on the top end!!?? The top end feels great, just like it used to be before it started messing up.

I am not sure how to check and see how my spak is and why does my car work great when I mess with the cap and rotor?? than it will mess up again really fast. ALso, why does it start and goes up on the RPMS than drops to normal????

There might be a possiblity of my timing mark being off and me runing very retarded (no pun intended ). How can I tell that????

Thanks Vader for the help.

 

Ok guys, i found out what the problem is with my car. i was thinkin hard about it being the fuel pump and i thought ''why not just take the air filter off the quadrajet and watch the gas'' so i did and when i pull the throttle i can see that the gas flow is inconsistent. it decreases the amount flowing when i pull it open hard and then shoots alot in. well i now know what it is, and my buddy's dad has a brand new pump that he can give me. the hard part isn't paying for it, its putting it in...

thanks alot everyone. helped alot

 

Great!!!

Quadrajet??? I thought it was TBI!

Anyways, I am changing my pump when I get some money. And I can show you how to do it the "HACK" way, which is building a door on the back hump of your car. If you want to do it right than you have to drop the tank and I would recomend at least one more person to help you out.

Sweet, I am glad you found out what the problem is.