1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

84SE Engine Swap Success! Surge at idle, clutch out.

Old 09-27-15, 11:33 PM
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Smile 84SE Engine Swap Success! Surge at idle, clutch out.

So, the spare 13b sat on the engine stand in my garage after purchasing from somebody here 16 years ago with me spinning it over with the flywheel once a month or so and spraying Marvel Mystery Oil in the intake ports occasionally.

Finally got around to the finishing details to fire it up: primed the oil system through the oil filter pedestal, checked fuel injection pressure for leaks, installed new plugs (BR8EQ14's), and spun it up. Fired within 1/2 second and I was shocked - no starter fluid needed, and no tinkering. Watched for oil pressure gauge to come up and got nothing, as I was getting a little worried, decided to tap the gauge and it flipped up to 60psi and never wavered.

No coolant or oil leaks, no hydraulic leaks, and only a little surging at idle from 500-2000rpm until it warmed up - likely just an intake feedback loop due to throttle position sensor needing an adjustment. Trying to drive it, the light flywheel (RB Aluminum) has considerably less momentum and it revved freely, but was surging between 200rpm on the low end to about 3k RPM - which I would expect out of an -SE that's been sitting so long. What's weird is that with Clutch pedal IN, the surging stops immediately and idle goes to 2k RPM and holds rock steady. Let the clutch OUT and it goes back to 'brap-ing' like a Bridgeport. Any hints?

In complete desert rat fashion, drove it around the neighborhood without a hood ripping up and down the side streets testing the new clutch disk, pressure plate (Exedy stage 1) and aluminum flywheel, and it revs like never before. Ran it down the local highway for a ten mile jaunt and coolant temp nor oil pressure wavered on the gauges.

At 220k miles on the original engine, I'm feeling like there's new life on this one. Can't wait to put more miles on it after a TPS adjustment and possibly Throttle Body Rod lubrication - which will be the next thing I do.

Special thanks to the board member who shipped me this engine so long ago!
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Old 09-28-15, 02:57 AM
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sounds like you had a good day.

any reason to believe there is an inconsistency in the function of the ignition system?
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Old 09-28-15, 10:18 AM
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Congrats on getting it running.

I consider you an authority on the GSL-SE 13b tuning and troubleshooting. I have a similar issue with my 1985 GSL-SE and surging on start-up. It starts without issue, but until it's warm, it will surge and I have to keep my foot in it until it's warm (about 2000 RPM). Mine only surges a few hundred RPM. Maybe 2000 to 2200. Once it's warm and the idle kicks down, it's fine. It idles around 1000 when warm.

Any tips on how to adjust the TPS the correct way? I've read a few things but thought I'd ask you.
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Old 09-28-15, 01:32 PM
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I use a home-made TPS 'light'. It's nothing more than 2 old filament light bulbs (12v) that I soldered together in the following configuration:

SPADE ...............Bulb 1 threaded portion

SPADE ...............BOTH Bulb bases

SPADE ................Bulb 2 threaded portion

This gives you 3 spade connectors, which plug into the Green Plug over by the AFM (and the fuel pump shunt connector, which is white). Plug the common into the 'mouth' of the 3-plug, and the other 2 bulb threaded portion spades into the 'eyes' on the connector. From there, you want to turn the TPS adjuster screw (flat blade, big wide screw) which is on the main throttle body rod to the forward end of the car. It's right next to the OMP rod connection.

With the engine NOT running, you can move the throttle at the gas pedal cable to 'reset' the rods, and get no lights, one light, or both lights. You want to adjust the screw until you get just barely ONE light lit. Each time you make an adjustment, give the throttle a 'blip' at the throttle body to force the TPS to move and reset under spring tension. When set properly, as the throttle comes back to idle rest, both lights will turn to ONE light, only. This gives the best steady state throttle response, and is what tells the engine when you've returned the gas pedal to zero.

Have at it and reply back if questions. I've decided after thinking about it that my 'surging' is probably caused by dry throttle body rods where they go through the TB, which is what typically causes surging in SE's. Apart from that, I'll also reset the TPS as defined above. I'm about 90% sure this will fix it - and the other 10% is on a vacuum leak due to a vacuum hose I forgot to hook up properly! What throws me off is that the idle goes rock-steady when you push the clutch in - as I have no explanation why that should happen - if anybody knows, I'm all ears! Good luck,

Edited to add: ignition system is new plugs, known good cap & rotor, and known good wires. The engine pulls strongly with no misses all the way up to 6k, and I didn't want to redline this engine until I know it's running well. Thanks for the suggestion, and I'll have another look at it.

Last edited by LongDuck; 09-28-15 at 01:35 PM. Reason: re: ignition system
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Old 09-28-15, 05:01 PM
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i had an AL flywheel back in the day in my -SE and the idle system is setup to work with the stock heavy one, and it kind of over responds. i ended up going to a heavier flywheel, so i didn't really fix it. i was thinking about putting a small restrictor in the BAC hose, to try and limit it a bit.

it might do to check the clutch switch too
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Old 09-28-15, 05:21 PM
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Well, pushing in the clutch is enacting a change - so the clutch switch seems to be 'working'; the question is, what does the clutch switch have to do with the BAC or Idle Compensation air circuit. That's where it's boggling my mind that the clutch would have anything to do with it.

Night and day - clutch out, trans in neutral, BRrraaa-BRrraaa-BRrraaa - push clutch IN, brrrrrrrrrrrrrrrrrrrr @2k RPM, no surge at all. Clutch OUT and back to surging. Weird!
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Old 09-29-15, 09:50 AM
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Thanks for the help on setting the TPS. I remembered I had built a 2nd gen code reader that sounded a lot like what you described with the lights. Come to find out, I had exactly what I need already. I was able to adjust the TPS to one light that was just flickering. When I plugged it in, it had two lights lite. I was able to decrease the idle. I still get the surging, but at least the car doesn't want to die before coming up to temp.



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Old 09-29-15, 08:02 PM
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Nice work! Looks downright professional compared to the rigged up,smoldered light bulbs I've been using for 20 years now. I had an idea to build a mounted fixture like yours that would remain in the engine bay and use switches to power up the various diagnostic and adjustment tools, but haven't gotten around to it yet.
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Old 09-29-15, 08:51 PM
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Originally Posted by KansasCityREPU View Post
Thanks for the help on setting the TPS. I remembered I had built a 2nd gen code reader that sounded a lot like what you described with the lights. Come to find out, I had exactly what I need already. I was able to adjust the TPS to one light that was just flickering. When I plugged it in, it had two lights lite. I was able to decrease the idle. I still get the surging, but at least the car doesn't want to die before coming up to temp.



Sounds like you have a small vacuum leak somewhere likely due to either a hard hose (rubber is not sealing) or gasket that is not sealing properly. Once it is warmed up the rubber on the hose heats up, becomes more pliable and then seals properly or the gasket expands and seals the leak. I would replace if you have not already all the vacuum lines on the engine and retighten your intake gasket, upper intake gasket and plenum gasket. Also check the clamps that hold the large hose coming off the AFM to the TB and make sure there is no air leaking in there also.
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Old 09-29-15, 11:16 PM
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Good advice, man - thanks.

When doing the engine replacement, I took out about 90% of the rubber vacuum and air handling hoses and replaced with blue silicone from Mazdatrix, bought by the foot. This helped with prior vacuum leaks, I'm sure, because most of the old brittle OEM hoses broke off in my hands when I replaced them. If nothing else, it's peace of mind that the silicone hoses should never need replacing.

Aside from that, I just got in from the garage and reset the TPS using my 20yr old fixture - which still works great. It was way off with no lights lit at idle, which tells me that it's part of the steady-state cruise surging which I felt to some degree on the maiden voyage of this engine being installed. I attribute the rest of the idle surging (clutch out) to be a combination of light flywheel and BAC feedback due to Throttle Body rods sticking - classic -SE surge cause. I removed the TB tonight and re-lubed the rods inside and out with PB Blaster. That should tell me whether I've figured it out as a combination of items.

When looking around, I noticed that my charcoal canister vacuum source isn't connected to anything. The purge valve which is normally hooked up to it is routed through the big hose to the side of the oil fill tube - and I can't find another location where the charcoal canister vacuum source should connect. Broke out the FSM to read through,
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Old 09-30-15, 09:11 AM
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Originally Posted by LongDuck View Post
Good advice, man - thanks.

When doing the engine replacement, I took out about 90% of the rubber vacuum and air handling hoses and replaced with blue silicone from Mazdatrix, bought by the foot. This helped with prior vacuum leaks, I'm sure, because most of the old brittle OEM hoses broke off in my hands when I replaced them. If nothing else, it's peace of mind that the silicone hoses should never need replacing.

Aside from that, I just got in from the garage and reset the TPS using my 20yr old fixture - which still works great. It was way off with no lights lit at idle, which tells me that it's part of the steady-state cruise surging which I felt to some degree on the maiden voyage of this engine being installed. I attribute the rest of the idle surging (clutch out) to be a combination of light flywheel and BAC feedback due to Throttle Body rods sticking - classic -SE surge cause. I removed the TB tonight and re-lubed the rods inside and out with PB Blaster. That should tell me whether I've figured it out as a combination of items.

When looking around, I noticed that my charcoal canister vacuum source isn't connected to anything. The purge valve which is normally hooked up to it is routed through the big hose to the side of the oil fill tube - and I can't find another location where the charcoal canister vacuum source should connect. Broke out the FSM to read through,
The small hose on the vacuum canister goes to the fitting right beside the large hose and runs back to the rear of the car underneath. The two hoses connect almost side by side about 6" from the canister.
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Old 10-03-15, 10:03 PM
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Took the upper intake manifold off today to check the vacuum line to the cold start assist which was unconnected. The vacuum feed hose was pulling significant suction, but reconnecting it didn't change the surging. I followed the above suggestion and installed a silicone hose insert in the intake feed to the BACV and this held the surging to a minimum.

Got it tuned well enough to get it emissions tested and passed no problem! Got it home and installed the Racing Beat header and presilencer and went for a celebratory drive at sunset. Running well, powerful, but sill surging about 500rpm with clutch out. Push the clutch in and it idles at 1400rpm rock steady - still has me stumped.
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Old 10-07-15, 08:12 PM
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Found it.

Bypass Air Control Valve vacuum source wasn't connected. This is the vacuum line which comes from the switching solenoid on the rats nest to the black volume chamber bolted to the center iron and then up from under the intake manifold to the front diaphragm valve on the BACV. The location of the vacuum nipple is one the inside of the diaphragm and I didn't see it until I removed the BACV to check for gasket leaks.

Thanks to all who responded,
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