Some Hesitation and missing at low RPM (UPDATE)

[revhardSHO]

My 89' SHO is giving me some trouble. Engine will start fine and idles normally. From idle(in nuetral) if you hit the gas it will bogg for approximatly 1/2 second and then spool up. It seems slower than normal to spool and has less throttle response in general. And its drive-ablitity has gone further out the window...

Now for the "moving" symptoms. In first throw 5th gear from ~1000-3400rpm ive noticed hesitation and inconsistant miss-firing. These symptoms occur under normal accelertion, and get worse under heavy acceleration.
At low rpms (1300-2200)under WOT the engine will backfire, and you'll hear the classic "POP" from the airbox. Hesitition is ALOT worse under WOT.

Now here is the strange part. Once the engine gets turning over ~3600rpm there is much less hesitation and virtually no missfire. Alot smoother has good power. although it does feel slightly weaker. The engine has 100K on it and there is no oil in the plug wells. the CE light is on, but i think the O2's are throwing codes. Im not about to go outside w/ a paperclip and flashlight to run the codes, maybe tommorow if it warms up...
and addvice would be appreciated.

thanks,

silas

<small>[ February 12, 2003, 08:30 PM: Message edited by: smithsil89SHO ]</small>

 

[drivinhard]

Sounds like maybe an ignition miss under load. Like a bad plug or wires.

I would start with the codes though, see what it's saying and go from there.

Also bad camshaft sensors will cause all kinds of weird things, backfires, hard starting, stumbling at low rpm, etc.

 

[sdpatt]

My first thoughts were like Mark's: bad plugs or wires. How old are the plugs? What brand are they? Is there oil in the plug wells? You should remove the plugs and check the gaps and the possibility of arc tracking down the side of the insulator. Old plug wires (how many years old are they?) can also cause a similar problem. This does sound like a weak spark misfire condition.

 

[BeatDaSHO]

it takes some time for the turbo to spool up thumbs_u

Greg

 

[revhardSHO]

Thanks for the replies...

Okay i just ran the codes.
Here is what i got:

24 -Intake Air Temperature (IAT) or Vane Air Temperature (VAT) sensor out of range

Now with engine running:

25 -Knock sensor not tested (ignore if not pinging)

41 -System lean
System was lean for 15 seconds or more (no HO2S switching)

91 -System running lean
Transmission SS 1 circuit/solenoid problem

Codes 41 and 91 indicate some sort of lean condition. What could be causing this? Maybe a bad fuel pump? I think its the original, and yes i can still hear it when you turn the ignition on. Bad 02 sensors? (what is the code for those anyway?)


engine is running alot better than it was yesterday. I added Fuel injector cleaner and it seemed better, but its hesitating some and occationally missing. No more backfiring. Still something is wrong.

The plugs have at least 35k and the wires have at least 45K, who knows they may be original.

what do you guys think? I think the wires may be at fault? Im worried about the lean codes. What could be the cause? The last thing i want is detonation

silas

<small>[ February 12, 2003, 08:34 PM: Message edited by: smithsil89SHO ]</small>

 

[rendyx]

I would look into the plugs and wires, as that's a fairly common cause of such a problem. However, the lean part makes me wonder. It might very well backfire if the system is lean. I'm not quite sure why though, as it probably isn't a sensor according to the computer.

 

[AutoSHO]

Clean you MAF!!! And that is all I have to say about that.

 

[sdpatt]

The intake air charge temperature sensor in the air filter box is out of range. Replace it and you may also cure the lean problem. Ignore the code 25 unless you are having a problem with pinging.

 

[bradman]

As Scott says, your first thing should be to clean the ACT sensor and run the codes again. If the 24 code is still there replace the ACT sensor. Once you clear the 24 code, if your HEGO's (O2's) are still indicating lean, then they probably need to be replaced. If they are the originals they are getting old and could be giving a false lean indication.

I had similar symptoms with my 89 where it would start and idle, but bogg when I applied any throttle. I was getting the HEGO lean codes in addition to the code indicating that the coolant temperature sensor was out of range. I changed both O2's and the coolant temp sensor at the same time and it cured the problem. Some will argue that the EEC doesn't take readings from the O2 sensors at start-up, so maybe it was just the coolant temp sensor that was my problem, but because our symptoms are similar, I think my experience is worth mentioning.

<small>[ February 13, 2003, 02:30 AM: Message edited by: bradman ]</small>

 

[revhardSHO]

thanks, i will be cleaning the ACT shortly and running the codes again.
let you know how i make out in a an hour or so.

silas

 

[Mark in PDX]

Hi Silas,
When I had codes 41 & 91, I replaces the 02's and this went away and so did the over-rich problem with my car.. The hesitation is due to it being flooded, so it takes a moment to get rid of that gas.. It will also eat your cats eventually...
I paid about 55 for new motorcraft o2's locally..
I'd just replace them.. too much headache otherwise..

 

[bradman]

I agree with Mark's analysis that due to the O2's false lean indication, the EEC compensates rich and dumps too much fuel for the engine to handle when you hit the throttle. In my case I think the bad ECT may have been a contributing factor. I bought my car from a used dealer who's mechanics couldn't diagnose the problem which had progressed to the point that the car would stall unless you held the rpms over 4000. oh_my It was virtually undriveable.

 

[revhardSHO]

Thanks for the replies everyone.
I cleaned the IAC and its still giving me code 24.

Like you guys said codes 41 and 91 are problably bad 02 sensors. On top of the 60K valve lash adjustment the car will be getting new plugs, wires, 02 sensors, and an IAC. Hopefully that will solve my problem.

silas

 

[revhardSHO]

Just installed new o2 sensors and the car is definitly running better. There is still some hesitation and missing at low rpms.
Ran the codes again and didnt get 91 or 41, inticating that my new 02 sensors are working.
I still got code 24 which means i'll be getting a new IAT sensor.
I also got this code:

22 MAP (vacuum) or BARO signal out of range

What could this be??? I have no idea what this could indicate?

I think new wires and a plug change should solve my hesitation/missing problem.

silas

 

[dward]

i am having the same issues. i have replaced plugs wires and coil and still nothing. my cel is not on. id like to know what it is too

 

[rubydist]

my experience is these engines will not run right if they are complaining about the IAT - you will need to fix that to make it run right.

the 22 code usually means you need a new barometric pressure sensor.

 

[sho4life]

so what was it? iat aic? baro? o2's? im going to try one at a time till i figure it out too