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Discussion Starter #1
When I advance the timing 15 distributor degrees it runs good. Rotate the dist back to normal position the problem comes back. This all happens parked in the drive way. Is it the cam sensor circuit?
 

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Have you checked the timing with a light? What's it set at?
 

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Note that when you check the ignition timing, you must remove the ECU input, by jumping the blue/red wire to black wire, in the little diagnostic box.
 

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When I advance the timing 15 distributor degrees it runs good. Rotate the dist back to normal position the problem comes back. This all happens parked in the drive way. Is it the cam sensor circuit?
[To me that sounds a lot like a loose crankshaft bolt or torn keyway. Are you torqued to 94 ft. lbs and no play in the crank gear? If everything is tight, follow Fordem and Bex's advice.
 

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A damaged crank keyway will cause the timing to be retarded which will be revealed in the suggested test - for me that's the quickest & easiest way.
 

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Discussion Starter #6
Parked in drive way. Distributor set at the factory 9 degree BTDC mark on dist housing. Start cold engine. Runs good with no bogging when goosed. Warms up but not yet fully hot and bogging starts, with occasional popping back up the carb. Immediately checked timing with timing light. Shows 9 BTDC at 800 RPM. Rev up engine and timing mark acts normal. Advanced the dist about 10 degrees and bogging is less. Immediately did a compression test: #1 190psi #2 190 #3 175 #4 180. (engine was hot by this time.) Timing light reflects what I do at the dist. Unplugged the air temp sensor: no noticeable affect. Unplugged the coolant temp sensor and bogging lessened. Engine hot by now. Measured ECT sensor and it was 360 ohms at 175 degrees F. which is what it should be. I checked the big timing gear bolt on the crank and it is tight, which doesnt really prove the key is ok. But I think the compression test proved it is.
BTW, a sheared timing gear key will not affect observed ignition timing because the distributor is physically tied to the timing gear on the crank by the belt and the pulley is bolted to the gear with 5 screws so stays as part of the gear. Thus this whole system will appear to be working normal even with a sheared key. Only a jumped belt will make the dist and timing mark on the pulley disagree with each other.
While I had the timing light out I aimed it down into the throttle body and could see gas striking the throttle plate. Bogging or not, I didnt see anything what I thought looked abnormal.
Cant figure out whats wrong.
 

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Sheared or wallowed key will however alter crank to cam relationship,
timing light will be fine as thats tied to the cam, But the pistons could be 5 degrees out from where they should be. Timing marks on the pulleys will line up, but won't line up with the piston position internally.

Check your crank keyway, and check valve lash, #3 is low, #4 is as well but not as bad. Do a dry warm compression test again, and a wet test, post results please.
 

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First, I would think that you don’t have a carb, no?? Second, your timing light scenario doesn’t indicate that you’ve removed the ECU from the circuit, which you MUST do.
You should advise exactly what the idle is doing from ‘start cold’. When your engine is cold, the ECU is injecting more air/fuel into the system to warm the car up, which hides various issues that become apparent once the engine is warmer.
By the way, the #1 cause of bogging/hesitation, is the EGR circuit. Have you tested that?
 

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Discussion Starter #10
I went straightr to the chase and removed the timing gear from the crank and everything was in perfect condition, including the belt and cam timing marks. Yes, just a throttle body. I always use the jumper to isolate the ECU but as others have noticed, it doesnt change the timing unless your AC is on or power steering pressure is high. When cold it idles fast mabe 1500rpm, then idles down to 800 after a minute. The EGR functions correctly, no sticking, passages not clogged. To make sure, I disconnected the EGR vacuum line so it couldnt open but that didnt cure the bogging issue.
 

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I don’t know where you got the info that the ECU doesn’t change your timing unless you have AC or PS. I have neither of them, and the ECU inputs into my timing.
I have the same 91 Tracker that you have - when it starts from cold, it revs to about 2000 rpm, then the throttle opener closes within about 5 seconds, and the idle drops to about 1500. And then it takes about 5 minutes for the idle slowly drop down to 800 rpm. A bit different than what you’re describing??
And in looking over your compression values - I find it somewhat difficult to believe that a 29 year old 8v, even when hot, can still get 190psi in a compression test. When new, they only pulled about 199psi...????? The norm for this age car, on a hot engine, is about 170psi...
 

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Discussion Starter #12
It has 151000 on the odometer. Maybe carbon buildup? Started it up cold this morning and came off fast idle in about 10 seconds. Sometimes longer. Will inspect vac hose to dashpot.
 

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And in looking over your compression values - I find it somewhat difficult to believe that a 29 year old 8v, even when hot, can still get 190psi in a compression test. When new, they only pulled about 199psi...????? The norm for this age car, on a hot engine, is about 170psi...
Vehicle age is not really a factor in compression numbers, engine wear (cylinder bore/rings) is the determining factor, and it is possible for a well maintained low mileage vehicle to have good compression numbers regardless of it's actual age.

Having said that - mileage is not a good indicator of engine wear as the majority of engine wear occurs directly after a cold start - you can also have city driven vehicles with relatively low mileage that, because they are only driven short distances and the engines never really reach operating temperature, they are more worn than engines in vehicles with significantly higher mileage that are primarily highway driven.
 

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Discussion Starter #14
My '95 tracker had 250000 miles and the pistons would slap until warmed up. Compro do it in and it was fun.ession was 180 in all cylinders. Then I overhauled it. I had a nice place to do it in and was fun. I enjoy solving car problems doing the fix but this come and go bogging problem in the '91 tracker has me stumped. Its gone on too long. Did find today why fast idle lasted so long. It was a badly cracked vac hose. Easy fix. When this rain ends will play with the TPS adjustment after looking over FixKick's TPS adjustment webpage.
 

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Discussion Starter #15
Cold engine started right up. Didnt start bogging until warmed up. Idling at 850. Went thru TPS adjustment and test procedures. Still bogged. Intentionaly misadjusted TPS : still bogged same as before. Readjusted TPS correctly. Let me discribe how the engine behaves when it bogs. I quickly open the throttle about half way and immediately it starts loosing rpm and almost comes to a stop and then quickly recovers and revs up to high speed. This all happens within a few seconds because its not under a load like when driving when the engine is in gear. Well, I tried something else; pinched shut the fuel return hose coming out of the regulator to increase the fuel pressure. All that did was to very slightly increase the idle rpm by enriching the fuel mixture. ( I originally said advancing the ignition timing stopped the bogging but actually it only lessens it. ) Then I killed it and couldnt get it started. This has happened a few times in the past on the road so was glad so I could investagate here in the driveway. First I removed spark plugs. They looked alittle sooty and were gaped .040". They were not wet. Cleaned off the insulators with a rag and regaped to .025 to help insure they arent misfiring. A long shot. Still wouldnt start. Put cyl #1 at TDC and looked at the rotor. It was pointing right at #1 spark plug. The dist cap looked clean inside. All looked good. I tried starting it and it started. BTW, I'm using a jumper wire under the hood for starting. I then notice that if I open the throttle a wee bit and hold it there as I goose it that it doesnt bog! So I screw in the throttle stop screw, the one thats never supposed to be touched, and I couldnt get it to bog any more. I adjusted the idle speed screw to bring the idle back down to 850 to compensate for the now slightly more open throttle plate. Rechecked TPS and still in spec. Someone in the past had monkeyed with the stop screw, paint broken, no plastic cap. Anyway, future days will tell. I will let everyone know the outcome one way or the other.
 

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Ah, hopefully you’ve found your problem. There’s a reason why no one is supposed to monkey around with that screw! And while it may be a typo, factory spec is .028” (.7mm) for the spark plugs.....
 

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Discussion Starter #17
Ah, hopefully you’ve found your problem. There’s a reason why no one is supposed to monkey around with that screw! And while it may be a typo, factory spec is .028” (.7mm) for the spark plugs.....
Ah, hopefully you’ve found your problem. There’s a reason why no one is supposed to monkey around with that screw! And while it may be a typo, factory spec is .028” (.7mm) for the spark plugs.....
Cold engine started right up. Didnt start bogging until warmed up. Idling at 850. Went thru TPS adjustment and test procedures. Still bogged. Intentionaly misadjusted TPS : still bogged same as before. Readjusted TPS correctly. Let me discribe how the engine behaves when it bogs. I quickly open the throttle about half way and immediately it starts loosing rpm and almost comes to a stop and then quickly recovers and revs up to high speed. This all happens within a few seconds because its not under a load like when driving when the engine is in gear. Well, I tried something else; pinched shut the fuel return hose coming out of the regulator to increase the fuel pressure. All that did was to very slightly increase the idle rpm by enriching the fuel mixture. ( I originally said advancing the ignition timing stopped the bogging but actually it only lessens it. ) Then I killed it and couldnt get it started. This has happened a few times in the past on the road so was glad so I could investagate here in the driveway. First I removed spark plugs. They looked alittle sooty and were gaped .040". They were not wet. Cleaned off the insulators with a rag and regaped to .025 to help insure they arent misfiring. A long shot. Still wouldnt start. Put cyl #1 at TDC and looked at the rotor. It was pointing right at #1 spark plug. The dist cap looked clean inside. All looked good. I tried starting it and it started. BTW, I'm using a jumper wire under the hood for starting. I then notice that if I open the throttle a wee bit and hold it there as I goose it that it doesnt bog! So I screw in the throttle stop screw, the one thats never supposed to be touched, and I couldnt get it to bog any more. I adjusted the idle speed screw to bring the idle back down to 850 to compensate for the now slightly more open throttle plate. Rechecked TPS and still in spec. Someone in the past had monkeyed with the stop screw, paint broken, no plastic cap. Anyway, future days will tell. I will let everyone know the outcome one way or the other.
 

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Discussion Starter #18
Well, the stop-screw was a dead end. The bogging/hard starting problem returned the next day. Nuts! A new light at the end of the tunnel: I was reading in this forum were someone with a '91 tracker had my same problems and he put on a new ECT sensor and problems gone! I recently checked mine and resistances looked ok. Assuming it is bad, I unplugged it and inserted a 165 ohm resister into the plug so the ECN would think coolant was at 180 degrees-- engine fully warmed up. So far no bogging or hard starting. Will take more driving to varify. Does take a little more cranking when cold but may be due to leaner mixture because ECN thinks engine is hot and doesnt need the richer mixture. I ordered a new ECT sensor just in case this works.
 

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Discussion Starter #19
Well, the stop-screw was a dead end. The bogging/hard starting problem returned the next day. Nuts! A new light at the end of the tunnel: I was reading in this forum were someone with a '91 tracker had my same problems and he put on a new ECT sensor and problems gone! I recently checked mine and resistances looked ok. Assuming it is bad, I unplugged it and inserted a 165 ohm resister into the plug so the ECN would think coolant was at 180 degrees-- engine fully warmed up. So far no bogging or hard starting. Will take more driving to varify. Does take a little more cranking when cold but may be due to leaner mixture because ECN thinks engine is hot and doesnt need the richer mixture. I ordered a new ECT sensor just in case this works.
 
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