caprice_2nv

Hope you guys can help me, I just got this car to replace my old daily driver and I've got 2 driveability issues with it. I searched for a while and could not find what I was looking for.

The car has a bog on acceleration at all times and it ranges in severity. No misfire at all it's smooth at all times just it bogs really bad. Sometimes it will barely get up to speed, and sometimes has a hard time keeping up to speed on hills without downshifting. If I step on the gas over 3/4 throttle and it bogs I can hear the air sucking in the air cleaner. This is my first car with EFI (all my previous cars have a qjet) but I know a bit about EFI. Anyways my problem felt like it could be a TPS, but it has not set a code for that. The only code it has set is code 23 (intake air temp sensor I think?).

My 2nd problem I think is related to the code I have, when I start the car cold it idles up to probably close to 2000rpm and stays there for several minutes before finally dropping down. Other than that it starts and idles perfect all the time.

One might suspect a fuel delivery problem if they test drove it, but the thing is I had a chance to drive this car about 3 years ago when it still belonged to the person I bought it from (it was in the dealership i worked at for service) and at that time it had the exact same bog which I at the time thought might be the fuel pump. However a fuel pump doesn't start failing and keep going for 3 years and 30k miles later still doing the same thing.

I thought about map sensor, or knock sensor (retarding timing), but like i said, no codes for those. The SES light only comes on occasionally when the car is warming up, other than that so far it seems to stay off.

Could the air temp sensor cause a bog, or just the fast idle? Can a map sensor or knock sensor problem not set a code?

Hope you guys can help me, I'm driving the car to work regularly now and can't pull out to pass anyone cause I don't know how bad the car will bog.

Thanks.

John 89 Formula

If you haven't done it already, a good tune up is where I would start, also a new fuel filter, and make sure the base timing is set to dead zero.

caprice_2nv

My plan is to fix the problem first, then get to the tune up stuff, other than fuel filter and PCV valve I am replacing ASAP.

My reasoning is that none of the regular tune up items will cause this problem. Also the plugs, wires cap and rotor all looked decent and I have no misfires.

Timing could be off but it wouldn't explain an intermittent lack of power. It would just have no power all the time. Timing fluctuations could cause my problem but I don't have access to a timing light right now or the time to check it. If the timing is doing weird things I have to figure out what is causing it.

What I'm looking for is some advice on likely causes for the problem and depending on price of the part I may just replace it and hope for the best. I don't really have any time to go and test all the items, but I don't have $$ to pay someone to diagnose it. Someone out there has to have enough experience to have a good idea what may cause it to act like this. The symptoms are very specific.

whitealexander

yes a new tune-up will be the first thing for you to do..

caprice_2nv

I see that you guys are parts replacers and not diagnosers. You can throw all the parts you want at a car and if you don't replace the right one it won't fix it. Keep that in mind. I'm trying to use logic here to fix the problem. We all know bad plugs and wires don't cause a bog, they cause random or steady misfires.

Anyways I thought of one other idea. There is a leak from somewhere in the AIR system, maybe one of the air tubes going into the head on the passenger side and it's making a ticking noise on acceleration or when the engine is revved. I'm now thinking it's possible that the knock sensor might be hearing this and retarding the timing when the ticking starts. I will try to fix the leak tomorrow and see what happens.

Any other advise besides a tune up is still much appreciated. Thanks.

dr.fiero

Have you scanned to see what the actual code being set is?

One thing for sure - if you have an IAT sensor failure or wiring to it, you'll never run right. If the sensor is shorted (or wiring) the ECM will see the air coming in as 255F (might be higher, can't remember). Anyhow.... very bad.... conversely, if the sensor or wiring is open, the ECM will see it as -40F! It will go CRAZY rich and again... never be right.

If your coolant temp sensor fails, it does the same trip - it's just worse. But that doesn't seem to be your problem.

Anyhow.... bog.... Fix that IAT first. A bad TPS you can sort of feel around it. Accelerate REALLY slowly. If it keeps getting faster, but then bogs if you blip it quicker.... that CAN be a TPS. TPS really only tells the ECM how fast the pedal changed position, not really where it is (though it does that as well) to determine the 'pump shot' (in carb terms).

If you simply have no power above a certain RPM that's a whole different issue.

caprice_2nv

Thank you dr.fiero, that helps a lot. The only code I got was code 23. I didn't see a problem with the wiring to the IAT sensor so I will try replacing that today. The car never seems to run offensively rich, it just runs too fast when cold.

The bog doesn't seem like it's the TPS the way you describe it now, cause if I change throttle position too fast, sometimes it will catch up within a couple seconds and sometimes it just keeps bogging. If it was the TPS then it should only act up for a second or 2 right? Also at slowly progressing medium throttle sometimes I can still feel a slight bog.

Thanks again, I will try a couple things today after work.

dr.fiero

Before you just replace it - Pin A11 is the ground at the ECM. Might want to check that wire at the sensor, then again for the signal on C12. I've seen those plugs go bad, especially if the wire is folded over. They break internally (the wire itself).

The sensor itself is just a thermistor. Meter across it and look for a resistance. Then hold it in your hand for a while to warm it (if it's cold out) and keep watching the reading. If it changes, it's probably OK.

caprice_2nv

Well I finally got a hold of a scanner to borrow (an old one but it seems to do the job), and I got an Alldata account for my car to help with the diagnostic procedures. Before this I already went and replaced the old fuel filter and replaced the fuel pressure line from the front back to the filter as it turned out to be leaking in more than one spot.

This did not affect anything.

Next I replaced the IAT sensor since my friend who works at a parts place got me one just in case, since I mentioned the code to him, and I was coming out to help him with his truck. I also verified no problem with wiring to the IAT sensor.

This didn't change anything either.

Next thing I tried a tank of 91 octane, my theory being that maybe it was carboned up really bad from 304k miles and the knock sensor was backing all the timing out. Anyways that was not it either.

Now I got the scanner on it driving today, have not had a code set since I started driving the car regularly. I have no Knock Retard happening at any type of throttle, even fast hard throttle, and no pinging either which makes me think I may have a problem with something pulling timing out. I still have to check the initial timing, but that wouldn't be the main problem because if it was retarded it would consistently have no power, not the intermittent surge that I've got. Also the scanner i have would not show me a lot of the Modes listed, spark advance being one of them that wouldn't work. There were several other modes that just came up "unused" even though I'm sure the car has them.

The TPS voltage seemed to be ranging okay but I didn't have the normal specs for it when I was driving and I can't remember exactly what it was reading, between 0.7v and 3.5v but I am only getting about 3/4 of WOT right now because of an incorrect TV cable for the transmission.

The biggest thing I think I found today was that the O2 sensor was not consistently switching back and forth while I drove. When cruising at speed I noticed it tended to go LEAN and then just stay there indefinately until I hit a hill where I had to keep giving more and more throttle and the car was losing speed then it would finally start switching back and forth again. I didn't get to watch it very much but at idle it seemed like it was switching back and forth every few seconds, and at higher RPM, but light throttle it would stop switching.

So even if the O2 sensor is not causing my issue, it needs one for maintenance so I will pick one up tomorrow and try it.

If that doesn't do it, the next things on my list are to try another ignition module, as I heard that can screw with timing if they're faulty. After that i will test the MAP sensor. If I'm still having problems at this point a fuel pressure test.

Think I'm on the right track guys?

thomas1976

I would go with the FP test and the TV cable first.

caprice_2nv

Well since the TV cable is obviously not causing a surge from the engine, and the engine is supposed to be working properly before doing any adjustments to the way the trans shifts, I will leave that until after. Also I don't have a fuel pressure gauge right now so the other stuff is getting done first. I already bought a replacement AC delco fuel pump to replace the old one just for reliability, so it will be getting installed soon anyways.

thomas1976

I had unstable FP once and it caused bog at acceleration and wen stumped. Uncorrect TV cable adjustment also makes the car drive as if somethings wrong. Thats why I shared.

caprice_2nv

No I can see fuel pressure being a problem, but since I already know I have a bad O2 sensor, and I don't have the means to check the fuel pressure right now it's easiest for me to do the obvious problem first. The tv cable will cause problems but not the surging I'm feeling. One day I'll get caught up with all these problems. At least with over 300k on it, almost everything will have been replaced except the engine and rear end.

tibbitt23451

I had the same problem until today. The hose on the fuel pump that connects it to the sending unit was split. My car would start fine & idle great. I could rev it up in neutral, no problems, but when I accelerated it would hesitate. Runs great now with a new $0.50 hose.

newts25th

I too have the same problem until the car gets hot. I start my car up first, it idles itself up and down until the car gets warm. But my car (92 RS 305tbi) has pinging issues and have fought with the timing ever since i got the car. It is suppose to be at dead on zero but I had to retard it back to -2 and that helped a lot. I have been told that the open element filter is the cause because the idle air temp is not where it is suppose to be. I too had a code for the IAT.

When you put an open element filter on there you take off the IAT and you stash it somewhere else. The engine cannot read the correct temp. I am in the process of finding the stock air box. I have replaced the following:
TPS
idle air control valve
Fuel pressure regulator
fuel filter
spark plugs
rotor
cap

I am thinking of replacing the coolant temp sensor as it only idles funny when it is cold. Although that isn't always the case. The car has a mind of its own.

caprice_2nv let me know what you find out. two heads are better than one!!

caprice_2nv

Well I finally fixed the problem today. I brought some beer to a local mechanic and gave him all the background on the problem. He suggested we check the timing, since I don't have a timing light I had not been able to check it. Anyways turns out it was so far over advanced that he could not find the mark at first. Set it to 0 and then when I pulled out I spun the tires by accident. I guess if the timing is advanced too far the computer will try and compensate by pulling the timing way out. Now it seems to have a lot more power and still no pinging at all :-)

Next I can get the tv cable replaced so I can achieve full throttle and it should work okay.

newts25th

well I am glad you found your problem I have checked my timing and I was close. I had to pull it back to -2 and the car still pings!!!! I am checking my timing chain next. It might be lose or have some slack in it.

Trick414

I see that two guys advised you to do a tune-up in the first place and you shot them down.

I'm certain that you know that setting the timing during a tune-up is part of the procedure.

hmx

Yeah, and then after crapping on them for being 'parts replacers' he replaced parts anyway.

I've got an '89 Chevy Caprice with TBI which had very similar problems after I replaced the engine, and it wasn't until I started datalogging the car using an ALDL cable and a laptop that I had enough data to determine what the problem was. Logging data is great because you can see whether your sensors are working or not and you won't have to waste money replacing things if they're within spec.

caprice_2nv

Well your very well right that timing "should" be part of a tune up, but since vehicles like these have not been commonly around for a while pretty well any common garage won't think of timing when they think of tune up. They only think of plugs, wires, cap, rotor and filters. Especially since a lot of guys don't have a timing light, but will do the actual tune up items at home. My 89 Caprice owner's manual actually classifies checking timing separately as an "emission control service" to be done every 30k. Usually timing does not just "go out" unless the distributor hold down bolt is loose, or the chain wears severely, or some other problem. Not trying to argue, just wanted you do see my point.

I went to a local garage where I know the guys, brought a case of beer and told him what it was doing, what I'd tried so far, and what I had found with the scanner. He immediately got his timing light and once he was actually able to find the mark we got it running great. The beer cost less than if I had to leave the car there and have them diagnose it by symptom.

Somebody likely did adjust my timing a while back and did it with the connector for the EST unplugged throwing it way off. All of my previous cars have been carbureted with no computer controls, so if the timing was off it would either have no power all the time or ping like crazy. I had no idea these things would compensate so much for timing the way it did, it was the weirdest thing ever. You would have sworn it was a lean bog if not for the fact that it did not ping ever.

Now with the timing set at 0 I can hear just the slightest bit of ping at light throttle which is more like the 305's I'm used to. I'm sure the timing chain is fairly worn with 305k miles on it, so I will replace it and the water pump eventually.

I finally have to give back the scanner tomorrow

hmx

If you read the sticker under the hood that resides on the fan cover, it says to disconnect the computer before setting the timing, as this sets the base timing. It's a brown wire on the left hand side near the A/C compressor. If you try and adjust timing with the timing light while the computer is connected, you'll be about 30° off, or at least mine was.

caprice_2nv

The wire your talking about is the one i'm assuming they left disconnected when they set the timing before. Maybe I used the wrong term for it. Anyways its set properly now and running fine. Thanks everyone for the help.

Racer86y

At least you did not have the problem i did.I bought my 90 camaro with bogging problem,replaced all sensors to find out afterwards that 2 plug wires were crossed.Runs great now but before me the guy had 2 wires crossed and sold cxar because of it.lol

jayjay007

You still on here, I'm having the same problem