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Electromagnetic Wave :-h
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May not be a full on missed ignition event but a partial combustion due to weak spark or incorrect mixture.

Just did a Rolla at work with worn ignition parts, it would buck and stumble a little at tip in but otherwise ran smooth if you were easy on it and even if you were into throttle it would clear up around 3500 RPM. New stuff, runs great any speed any RPM and any throttle position. It was getting partial combustion on some cylinders some times.
 

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Discussion Starter #44
May not be a full on missed ignition event but a partial combustion due to weak spark or incorrect mixture.

Just did a Rolla at work with worn ignition parts, it would buck and stumble a little at tip in but otherwise ran smooth if you were easy on it and even if you were into throttle it would clear up around 3500 RPM. New stuff, runs great any speed any RPM and any throttle position. It was getting partial combustion on some cylinders some times.
Worn ignition parts? Can you give specifics?
 

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Different car, different parts, you don't have a cap and rotor with plug wires.
 

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Discussion Starter #46 (Edited)
Update:

I replaced my IACV on Sunday and the car started idling perfectly. No more high idle and no more idle surge (although the idle changes from 650-900 whenever it feels like it). I've driven about 50 miles and have not seen the CEL come back yet. This is a big relief. I also changed my drive belt with a gatorback belt. No more squeaks. :)

Unfortunately though, I STILL have hesitation. Nothing has changed. It's still an intermittent thing. Sometimes I'll have nice, smooth power and other times I won't (all during the same driving session).

I've sprayed the intake manifold around where the gasket sits with intake cleaner and I did not see anything abnormal or hear audible changes in the motor. I really don't think the gasket is leaking, especially with perfect LTFT's. And just to add, I generally get around 28mpg city/hwy driving.

The last thing I can think of is that I really could be leaking compression based on how the spark plug looked. I'm going to replace the spark plugs in case I over-tightened them and damaged the seals. I'll torque them down appropriately this time.

In addition to what Bitter said, this is something I found on another site:

"Over-torquing a spark plug can distort and break the seal between the metal shell and porcelain insulator, which causes combustion gases to leak into the spark plug boot and blow it off the spark plug. If a spark plug boot keeps blowing off, suspect a seal leak caused by an over-torqued spark plug."



Mine:
 

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Electromagnetic Wave :-h
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Did you reset the ECU after the IACV replacement?
 

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Electromagnetic Wave :-h
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Unfortunately though, I STILL have hesitation. Nothing has changed. It's still an intermittent thing. Sometimes I'll have nice, smooth power and other times I won't (all during the same driving session).
Yes, I disconnected the negative terminal during the entire replacement process.
Give it about a tank of gas to settle down. After a reset, you will hit points in the fuel map where it needs to make adjustments. If you are still having issues after a tank, its time to start troubleshooting again.
 

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Discussion Starter #50
Just an update, I've driven a good 300 miles by now and I'm still having intermittent hesitation issues. Besides leaking compression through the spark plugs, I can't think of anything else to check.
 

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Those intake gaskets are easy to change, so why not just as a 'cover all bases' step. Next up I'd take a closer look at O2 feedback to see if it's a lean issue or rich issue. It's probably a lean problem, most hesitation issues are. I had a Caddy in the shop the past week that had 2 leaky fuel injectors AND a bad O2 sensor, it would go lean under load on one bank badly then steadily miss worse and worse at idle as two cylinders flooded out. Talk about conflicting problems! Once the injectors were replaced it would still miss sometimes at idle in a predictable pattern, you could watch injector time and sft drift apart between the two banks as it started to misfire then BOOM snap back to where they should be and it ran fine, then repeat the cycle. Replaced the stuck O2 sensor and it was all fixed. Turns out the connector was corroded and there was a bridge between the heater and feedback circuits.
 

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Let's back up a step. What do you define as a "hesitation"?

Is it a defined pause in the application of engine power? Can you hear/feel a miss or stumble in the motor? Is the motor running smooth or vibrating a lot? Bitter's scanner test would reveal these issues with either the ignition or with fuel delivery.

Or do you feel the hesitation in the power being applied to the wheels? Does it feel jerky when cruising or when applying the throttle in the gear range you mentioned in an earlier post? This could come from a mostly worn clutch or slipping automatic transmission, which is why I asked that question earlier. Our 1990 Celica GTS had this problem; solved with a new clutch.

Hope this helps.
Dentman
 

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Discussion Starter #53 (Edited)
Let's back up a step. What do you define as a "hesitation"?

Is it a defined pause in the application of engine power? Can you hear/feel a miss or stumble in the motor? Is the motor running smooth or vibrating a lot? Bitter's scanner test would reveal these issues with either the ignition or with fuel delivery.

Or do you feel the hesitation in the power being applied to the wheels? Does it feel jerky when cruising or when applying the throttle in the gear range you mentioned in an earlier post? This could come from a mostly worn clutch or slipping automatic transmission, which is why I asked that question earlier. Our 1990 Celica GTS had this problem; solved with a new clutch.

Hope this helps.
Dentman
I define "hesitation" as a lack of increase in power throughout the rpm range. When you are stepping on the throttle, through out the power band, you will feel the car pull and then all of a sudden it will stumble/hesitate for a couple seconds (as if applying brakes or taking your foot off the throttle), and then suddenly pull again. Strangely enough, the problem is almost non-existent in 5th gear.

If my issue was represented on a dyno chart, I feel that it would look like this:



Bitter - can you explain the O2 feedback in more layman's terms? How would I go about troubleshooting that? I do have an obd2 scanner.
 

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Electromagnetic Wave :-h
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Have you checked the VVT oil screen?

What is the Date of Manufacture shown on the door?
 

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Discussion Starter #56
Have you checked the VVT oil screen?

What is the Date of Manufacture shown on the door?
I have not checked the oil screen. Can that affect performance in such a way that I've described? The Date of Manufacture on the door is 10/01.

Bitter said:
I understand how the O2 sensor works. I was really trying to understand what you're doing to determine if the motor was going lean and/or misfiring. Was it just by checking stft/ltft?

Here is a read out from my scanner of my O2 sensor..


For the first 20 seconds it is idling at 750 rpms. Then I held it at 2k up until about 35 seconds, and then back down to base idle from there on out. From my understanding, the sensor is working correctly.
 

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Yes, that looks good. Now, lets see feedback when it's hesitating.
 

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Electromagnetic Wave :-h
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The Date of Manufacture on the door is 10/01.
Subject to oil burning issues.
Yes, that looks good.
While that is a good sign, it does not necessarily mean that it is detecting the correct AFR. Time to look at the LTFTs again.

I am by no means an engine expert. But, everything I've seen said running rich. The LTFTs, troubles in warm weather, etc. But, the P0505 has been cleared. :thumbup:

I have not checked the oil screen.
Can't hurt to check it. As I recall, earlier models do not toss a CEL on VVT range errors.
 

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Discussion Starter #59
Subject to oil burning issues.While that is a good sign, it does not necessarily mean that it is detecting the correct AFR. Time to look at the LTFTs again.

I am by no means an engine expert. But, everything I've seen said running rich. The LTFTs, troubles in warm weather, etc. But, the P0505 has been cleared. :thumbup:
I don't think it is running rich. I'm getting pretty good gas mileage (27-29 city/hwy combined) and no black smoke from the tail pipe. What should I look out for in LTFTs?

Bitter said:
Yes, that looks good. Now, lets see feedback when it's hesitating.
Is there anything in particular to look out for in the graph when it's hesitating?
 

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Electromagnetic Wave :-h
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I don't think it is running rich. I'm getting pretty good gas mileage (27-29 city/hwy combined) and no black smoke from the tail pipe. What should I look out for in LTFTs?
Apologies. I was thinking of a different thread. You said LTFT's were good.
Is there anything in particular to look out for in the graph when it's hesitating?
MAF, timing, temps, etc.
 
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