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Turbo Dodge Help Urgent help when something goes wrong with your Dodge and you can't figure out what the problem is. Troubleshooting help and the place to post when you're stuck with a broken car and have to get to work the next day.

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Old 04-10-2013, 08:00 AM   #1
Hesitation and stumbling at certain throttle positions  
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So the car developed some new weird issues during the last race. At certain mid throttle positions it would randomly start bucking and stumbling. We replicated it in the pits, you could open the throttle ~1/2 - 2/3 and it wouldn't rev. instead it would fluctuate up and down a few times, then slowly build up. If you snapped it WOT it would act normal again.

On track it would occasionally stall out and die on shifts. As soon as you came off the gas and put the clutch in it would turn off, and I'd just dump the clutch and pop start it again. It also wasn't consistent in power delivery. At WOT you'd feel it pull, then back off, then pull again. Not always at the same RPM.

We ended up replacing the throttle body, and that seemed to help, but it did repeat the symptoms a few more times later in the day. The car has never done this before. We did have electrical issues the day prior. The O2 sensor wire bundle hit the turbo outlet and melted, shorting some things out (fuel, ignition, etc). Also caused a code 11 to be thrown, which really sent us on a wild goose chase. We did get those issues solved, but the hesitation issues listed above then greeted us.

I'm hoping that the replacement throttle body was just not 100% good and that really is the issue, but does anyone have other ideas? This race we were running the stock '89 computer with a '88 TII engine, with the '89 head and intake on it. (I know, it's a cluster-F, but you make due when you're racing cheap cars)
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Old 04-10-2013, 06:51 PM   #2
Re: Hesitation and stumbling at certain throttle positions  
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You have to verify all of your basics are correct...
Fuel Pressure(especially while the problem is present)
Ignition...
a)Capable of minimum 25 KV
b)No Arcing, use water test
c)Plugs are gapped properly and not fouled
Cam Timing
Ignition Timing
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Old 04-10-2013, 09:02 PM   #3
Re: Hesitation and stumbling at certain throttle positions  
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I can confirm a few of those already.

Cam timing is correct. It was checked 3 times before the engine went in the car

Ignition timing should be correct. We set it with a light when we swapped distributors chasing a code 11 the day before.

plugs are gapped to the stock .035 as called out by the sticker on the hood.

I believe fuel pressure to be ok, but i really need to put a gauge on it to confirm.

I will have to do the other tests.


Is it at all possible that our theory that something is wrong with reading the throttle position holds any ground?
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Old 04-11-2013, 05:18 AM   #4
Re: Hesitation and stumbling at certain throttle positions  
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Without any codes stored in memory it is doubtful that there is an issue with the TPS but you can backprobe the signal and signal return line and read output voltage.
You can also check Map output compared to vacuum/pressure when the problem occurs.

Be sure all of your engine grounds are connected/tight/clean especially from right rear intake to the firewall.
Rum a wiggle test on all wiring/connectors to attempt to simulate the condition.

FUEL PRESSURE
http://www.turbododge.com/forums/f4/...-93-turbo.html

MAP OUTPUT
http://www.turbododge.com/forums/f4/...agnostics.html
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Old 04-11-2013, 06:49 AM   #5
Re: Hesitation and stumbling at certain throttle positions  
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Thank you sir.

I did check codes again last night, and it's throwing a code 13. however that is new. It was not throwing that one at the race when this was happening. Not saying it isn't related, just stating the timeline.

I'll run through all the diagnostics you pointed to and see what I can find.
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Old 04-13-2013, 12:27 PM   #6
Re: Hesitation and stumbling at certain throttle positions  
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whatever the case, dont allow it to stumble or backfire under boost or youll crack pistons
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Old 04-16-2013, 03:13 PM   #7
Re: Hesitation and stumbling at certain throttle positions  
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oops. Ran a good 5 laps with it doing that trying to figure out what the hell was happening. No cracked pistons (engine is already in pieces). we did spin two bearings when something in the cooling system failed and our temps went from ~190 to ~240 in a single lap.

A friend pointed out something that makes sense. Since the short we fixed the day prior was in the O2 wire bundle, there might be other damage to that bundle and the car might not be reading the O2 correctly, and therefore not responding correctly. It's making the WOT transition right, but not consistently making the mid throttle position changes right. I'm going to rebuild that piece of the harness with new wire/connectors to eliminate that as a potential problem.
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Old 04-16-2013, 03:27 PM   #8
Re: Hesitation and stumbling at certain throttle positions  
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O2 is only a "fuel trimmer" and is only a player during idle and no load cruise conditions.
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Old 04-16-2013, 03:32 PM   #9
Re: Hesitation and stumbling at certain throttle positions  
Garrett Booster
 
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Quote:
Originally Posted by NAJ View Post
O2 is only a "fuel trimmer" and is only a player during idle and no load cruise conditions.
Well, rebuilding the harness may still help. Idle was significantly different after fixing our short problem, and nothing else really changed on the car. I'd rather be safe than sorry with this.
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