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Part throttle cut out under boost


BlueCuda
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My car that I only have 20 miles on since I got it running is running well for the most part.  If I am pulling a hill where it is making boost but I am not applying the throttle hard it cuts in and out a little bit.  It runs great under heavy throttle or cruise but part throttle under boost it could be better.  

I do know the vacuum advance is in good shape, the original car I purchased happened to have two distributors in the trunk and one of them appeared to be brand new and I have checked the diaphragm on it and it works.  My only drives have been with the timing set at 5*, I have since set it to the correct 10* but I haven't driven it yet.  The 5* was the lucky stab that I forgot to double check.  

EGR, I plugged the passage in the intake when I had the intake off. I tapped a freeze plug into it on the engine side.  However the actual EGR valve is still there and has no vacuum or anything hooked up to it.  I do plan on making a block off plate for it I just haven't yet.  I am thinking this may be my problem?  

It has all new plugs, wires, cap, rotor, and fuel filter.  I found a receipt showing the injectors were flowed in 2019, they were flowed pretty close to the time of death of the original engine best I can tell.  

Anyways, thoughts?  

 

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You can always tap the EGR port to use a threaded plug for it. But it may be better to do that on the head itself so you aren't allowing hot exhaust gasses into the intake manifold (keeps it cooler) 

As for the part throttle concern what did you gap your spark plugs to? Should be around .26-.28

Mechanical or hydraulic lifter setup in your engine? Done a TPS reset?

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I don't recall what I gapped them at, it was whatever was printed on the underhood sticker.  

I have not done a TPS reset, a little scared to mess with it because it starts and idles perfect haha, I will add that to my list of things to try.

On the EGR I blocked it off right at the head but on the intake side.  I happened to have a freeze plug that press fit perfectly in there.  I'm going to make a block off plate this weekend and remove the old valve.  

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Turbo Cary mentioning the TPS made me think of something. The TPS might have bad spots in it--they wear out over time. If you have an analog multimeter, you can sweep test the TPS and see any bad spots. If you search here for "sweep test" you'll find the procedure. I think it's in the FSM too but it's been a while since I've looked.

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For the record it doesn't need to be an analog meter; a digital one will work fine. Just make sure the voltage across the TPS increases and decreases smoothly as you slowly open and close the throttle plate

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In the end your going to have to have a way to monitor your fuel pressure and air flow. I suggested in a prior post about how to  achieve it. If you don"t have a way to see how much fuel pressure and airflow (via a Wideband and a FPG) your producing at idle, midrange and on boost ,your just spinning your wheels and it will be difficult for anyone to be able to help you with any kind of  a viable or accurate answer.

Bill

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I have been doing this with an open stock downpipe with a stub of pipe off of it.  The car came with a 3" system that looks real nice but didn't fit worth a damn.  That is getting taken care of this weekend and I will have a wideband going soon, this weekend if the AEM one that came with the car works.  If not I am going to upgrade the wideband setup on my other car and move the LC2 over to the conquest.  

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If I were you I would put the Maf Translator and 3"Maf back on the car. This set up is the quickest and least expensive way to achieve control over your fuel/air  along with a Fuel pressure gauge, adjustable RRBCFPR and  a Wideband AFR  to have control over your engine and what it is doing as far as air and fuel . Been at it since 2002 and this is the best advice I can give you to keep a car as close to stock as possible and still have some control over how it runs. I have been the modified stock air can and the 1st gen mas route. Unless you decide to go MPI or a engine transplant (LS1 or the like) I feel the MAF Translator is a good way to go.

 

P.S. Don't let the 6.5 thousand posts fool you!! I had over 14,000 prior to the website crashing.

 

Bill

Edited by Caliber308
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Bill, I sold the Maf T haha a little late now.  If I can't get a handle on things I will megasquirt it.  I have an MS3X on my other car so I know the platform well and I like it.  I really just want this one to be right stock at the moment and its getting there.  

I got a ton done on the car yesterday, fixed the alternator, and got the exhaust system adjusted to fit right and mounted securely.  Its a nice mandrel bent 3" system with a Dynomax muffler.  Super quite in the car but is pretty loud on the outside.  I don't know what brand or if it was custom made but it sure didn't fit very good, we had to cut the turbo flange %95 off and twist it and reweld so it would all fit. Then put a 3" V band underneath, welded the slip joint up, and added some hangers to catch some stock mounting points.  So far no rattles.   I am not sure how the previous owner even got it hooked up?  The floor is beat up where it was hitting at one point.  

 

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Glad you got your exhaust in. Back in the mid 2000s myself and my buddy who owns a muffler shop in Montana built from scratch a 2 1/2" downpipe back exhaust.Then a couple of years later I installed D-2 coilovers adjusted all the way down. Always on the look out for speed bumps, deep dips and never park on dry grass.  😉

Bill

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Ok I have some Data.  My son and I drove it about 40 miles today.  Runs perfect at low throttle and cruise, still cuts out under much load with boost.  

When we got home I found the power harness for my wideband that I was missing so i got that hooked up and a boost gauge hooked up.  Its indicating about 11-14PSI when it really is maxing out at 9 or so.  It goes into boost on the stock gauge sooner than it actually gets in to boost(no surprise).  Air fuel ratios are great at idle and cruising around but as soon as you lean into the boost it goes straight into the 10s and if you hammer on it it goes 10.00(low as the meter reads) and it obviously can't keep it lit so it cuts out.  

Thoughts?  I have yet to check fuel pressure so that is on the list.  I have two other sets of injectors so I could swap the secondary injector and give it a try.  Injector clips are fresh.  

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Your experience matches what I've seen with a wideband on both of my stock Starquests. When you get into boost, the factory computer practically drowns the engine in fuel. Neither of them cut out or stuttered when everything else was mechanically sound, though.

What kind of plugs did you use? NGK 7031s are the only ones that have ever worked well for me.

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I agree with what Obsolete posted. It does it too with a 1st gen mas setup. Stomp on it and the wideband goes to 10.0 afr. This is why I suggested a Maf-T set up in a prior post, you need or want the control over the Air/Fuel ratio as much as is possible on these cars. Also, if you are running aftermarket injectors, you need to up the fuel pressure for them to atomize properly or else they will  not spray correctly and drip fuel. Staying completely stock with your fuel system is sometimes not a option. Install a Fuel pressure gauge and a Fuel pressure regulator. I have suggested all these things in prior posts in this thread. As Obsolete suggested, use NGK BUR7EA-11 spark plugs, I gap mine at appox. .44  or whatever works for your set up ( trial and error). You want the largest gap possible prior to flame out.

 

Good Luck,

Bill

Edited by Caliber308
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I did get this thing to pull cleanly through a few gears one morning, it was 12* outside so it was able to burn the fuel with that super dense air.  

I don't know the exact part number for my plugs, I ordered them from MKS for the stock G54B when I ordered plugs wires cap and rotor.  They are gapped to factory gap.  I do plan to replace the coil just because it looks either original or just old.  I tossed about 3 or 4 MSD blaster coils a year or two ago and now I am kicking myself for that move.  

I'll check fuel pressure and replace the coil and report back.  I will also do a smoke test on my turbo plumbing to see if I have any leaks.  

 

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If you want to check all the hoses for leaks, spray the entire engine bay with carb. cleaner while the engine is running. If you hear the idle go up where your spraying, there is a air leak.

Bill

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My Dad has a smoke generator we use for checking for crank case leaks.  Its super handy for stuff like this because it uses a tiny amount of compressed air and will lightly pressurize the test subject after a few minutes and the smoke will emit from any leaks.  Smells bad, works great.  

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I have done nothing to fix this and it is still doing it!  wt....! ha

I got to drive it some more last night with the wideband on.  I am going to swap the secondary injector just to see.  It gets rich anytime you get up in RPM regardless of boost.  Even a slow pull up to 4500 it goes rich into the 10s with zero boost.  The secondary injector I had at the house is plugged with varnish so I need to make a trip out to my parts beater and see what its like.  

Beyond this it feels good to have one of these to drive again, this engine is smooth as glass so much so it worries me lol.  

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23 minutes ago, admin_JAinsworth said:

Check your CTS (coolant temperature sensor). A bad one can cause similar issues. The procedures are in the FSM.

Jimmy

That is a great idea, thanks!  

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Just as I thought I found a pretty massive leak in the turbo plumbing.  The hose clamps for the coupler between the OVC pipe and throttle body were as loose as could be.  I had checked over every other joint in the plumbing multiple times but never checked the easiest one!  

I tightened that coupling and

The factory boost gauge reads 8psi and matches the mechanical gauge.  

It doesn't sound like it has a big air leak!

The air fuel reads in the mid 11s wide open throttle.  

It pulls cleanly at wide open throttle.

Just for the record whenever I see a forum post without a resolution I always assume it was some dumba** mistake like this one.  So I wanted to follow up to confirm it was indeed a dumba** mistake.  Thank you for all the replies.  

 

 

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