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Old 07-01-2018, 11:39 PM   #1
maxitoman007
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Default 740 Turbo Extremely Sluggish. Builds Boost but No Power

So I just recently completed a head gasket job as well as a wire tuck on my 740 turbo. Now the car is extremely sluggish off the line and jerks during acceleration. This only happens until around 4k rpm where the power finally comes back on. My first thought was that I skipped a tooth on the timing belt and that my timing was now extremely retarded resulting in the powerband being shifted way up, but I checked the timing marks and all seems well. I do also have a wideband and nothing abnormal seemed to be happening with the AFRs

It is a very odd sensation. Pedal to the floor in second and you can hear the turbo spooling, see it build to 15 psi (out of 23) on the gauge but feel nothing going to the ground, that is until 4k. Not feeling the power makes me think boost leak but then it wouldn't have shown boost building on the gauge either.

To me it still seems like timing although this wouldn't explain the rough acceleration. Other things I've thought could be causing it is the knock sensor (which can pull timing), spark plugs (cleaned out the ignition chambers of the head with a wire brush on a drill with the plugs still in). I've also heard of hoses collapsing under boost (but this never happened before).

Any input is appreciated. the car ran great before aside from the coolant spraying out from the head gasket. It ran much better than it does now.

Last edited by maxitoman007; 07-01-2018 at 11:44 PM..
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Old 07-02-2018, 09:53 AM   #2
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I would check first to be sure you have your grounds all secured properly.

Then I would check for boost leaks. It's entirely plausible that your car is detecting air and adding a ton of fuel and this is where your bog is coming from.
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Old 07-02-2018, 11:40 AM   #3
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So under 4000rpm the engine feels like it is bogging and not making power and over 4000rpm it picks up and smooths out?

Do you have a wideband? Could be a failed FPR causing the engine to dump fuel and until the rpm's are high enough the engine cannot deal with that much fuel until the revs are high enough, fairly common issue.

If you remove the vac line to the front of the FPR with the engine off does it stink like fuel? or when running does it spray fuel at you?
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Old 07-02-2018, 01:50 PM   #4
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Hmm, never thought about considering fuel as a culprit. The car ran great before I did all the work and although I did change the fuel rail, I used the same injectors and fpr. The car idles great and AFRs look solid. Don’t think the bogging is from being rich.

As for grounds, the only thing that comes to mind is the fact that I don’t have the ground strap from the valve cover to the firewall reinstalled yet. All the other grounds I believe I put back. Are there any I should look at that could cause this?

Haven’t done a boost leak test but all the clamps I can see look firmly secured and I don’t see/feel any tears in the hoses.
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Old 07-02-2018, 03:16 PM   #5
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You probably put the belt on wrong.

Take off the upper cover and use a strong light on the belt guides on the crank sprocket and check the notch is lined up with the casting on the block.

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Old 07-02-2018, 06:32 PM   #6
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notch is inline with the casting on the block, just checked. That said, I did just notice that the belt seems oddly loose on the long run going from the cam gear to the intermediate shaft gear it can easily be pushed in with a finger and can be flipped nearly 180 degrees. The belt has been on for less than a thousand miles so i don't see it being stretched already. My cam gear is adjustable and uses the hex bolts so the gear doesn't have to be removed for adjustment. Figured this may help make the diagnosis easier by testing certain adjustments.
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Old 07-02-2018, 08:55 PM   #7
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Quote:
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notch is inline with the casting on the block, just checked. That said, I did just notice that the belt seems oddly loose on the long run going from the cam gear to the intermediate shaft gear it can easily be pushed in with a finger and can be flipped nearly 180 degrees. The belt has been on for less than a thousand miles so i don't see it being stretched already. My cam gear is adjustable and uses the hex bolts so the gear doesn't have to be removed for adjustment. Figured this may help make the diagnosis easier by testing certain adjustments.
Did you wrap it along the pulleys in the correct order so all the slack was on the run of belt where the tensioner is? First time I did it I had too much slack between the intermediate shaft and cam pulleys.
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Old 07-02-2018, 10:18 PM   #8
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I’m not sure. If I wrapped the belt wrong would that have the same effect of skipping a tooth? Is there a set, good way to wrap the belt with the lower timing cover on?
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Old 07-02-2018, 10:26 PM   #9
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I did just notice that the belt seems oddly loose on the long run going from the cam gear to the intermediate shaft gear it can easily be pushed in with a finger and can be flipped nearly 180 degrees. The belt has been on for less than a thousand miles
Depending on exactly where the crank stopped, the cam could "spring" forward and all the slack could end up on the "wrong" side of the run. Have you retensioned the belt since installation (as recommended in any manual)? Pull out the big rubber plug on the belt cover (if you have one), loosen the nut inside 1/2 a turn or so, turn the crank clockwise a bit to remove all slack on the "intermediate" side, retighten the nut.
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Old 07-02-2018, 10:36 PM   #10
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I have only driven the car maybe 10 miles after the head gasket job. Much less than the amount recommended before retentioning. I have tried loosening and retightening the bolt on the tensioner but seemed to only help temporarily, once I pushed on the long run again all the slack was back.
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Old 07-02-2018, 10:50 PM   #11
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I have tried loosening and retightening the bolt on the tensioner but seemed to only help temporarily, once I pushed on the long run again all the slack was back.
Just covering all the bases here... There should be a big thick washer behind the nut, otherwise it can "miss" the tensioner's hollow hub. The nut gets torqued to 37 ft-lbs. The big spring on the tensioner is in place? Any tensioner "installation" locking pin has been removed? The tensioner actually swings freely (against spring pressure) when not torqued down? You remembered to swear at it and throw a random tool across the shop?
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Old 07-02-2018, 10:58 PM   #12
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Only thing I didn’t do out of that list is use a torque spec on the nut. Figured it wouldnt matter. Cant see the torque causing all the issues I’m experiencing, must be something else going on...

Last edited by maxitoman007; 07-03-2018 at 04:57 AM..
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Old 07-03-2018, 12:51 PM   #13
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Bump, still need ideas.
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Old 07-03-2018, 02:38 PM   #14
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I'm thinking it needs the ground connection between the valve cover and the fire wall. There are 2 of them, one on each side of the rear of the valve cover.
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Old 07-03-2018, 02:51 PM   #15
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I've only ever had one strap there but I'll be sure to reinstall.

I have done some more research and I may have an idea of what is going on. I recently stumbled across a thread made by someone seemingly having the same symptoms as me, here's the link: http://forums.turbobricks.com/showthread.php?t=122681

In the end, the issue ended up being with the guy's knock sensor. This had me thinking and I eventually found this page: https://www.volvoclub.org.uk/faq/Eng...ngaKnockSensor

Now the parts I found interesting about the FAQ were these:

" [Other symptoms] Retarded timing, acting as though no fuel is reaching the engine."

"Make sure the wiring feed to the knock sensor is not close to the alternator: anecdotal reports of interference and retarded timing upon acceleration were solved by moving this wire. Some electromagnetic interference from the alternator is the likely cause."

Is the knock sensor wire shielded from the factory? I did have to cut back down the harness to reveal more of the knock sensor wire in order for it to reach after my wire tuck. The wire going to the knock sensor right now is a green wire with no visible shielding (unless its in the wire). I could have definitely routed it past the alternator.
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Old 07-03-2018, 03:12 PM   #16
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Failure to rev can be incorrect cam timing, retarded ignition timing, or lean in my experience.

I wanna believe you that your cam timing is correct, but triple check.

I use a smoke machine to find air leaks.

No misfiring?! Does it rev freely in neutral?
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Old 07-03-2018, 03:19 PM   #17
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in neutral it revs free as can be, no misfires. I've checked the marks and they all align after several rotations. Also i'm using the notch in the washer on the crank gear not the line on the harmonic balancer to make sure the crank is at tdc. The slack in the belt is throwing me off but I have a feeling that its unrelated. As long as everything is in time, it should work right?
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Old 07-03-2018, 05:46 PM   #18
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Update:

Here's what I did:
- put ground strap back on
- re-tensioned timing belt (managed to get the slack taken up)
- checked cam timing (for like the fifth time. All marks lined up perfect. I used the notch in the washer on the cam gear not the harmonic balancer)
- re routed knock sensor wire away from alternator
- checked base ignition timing (was 12 degrees btdc bang on)
- made sure timing advanced in neutral by manually turning the throttle drum (timing advanced as rpm increased as expected)
- unplugged maf while car was running (car almost died so that's good)
- unplugged the knock sensor while engine was running (No change. Timing still advanced as normal while manually turning the throttle drum)

All tests were done with the car warmed up and in open loop, I can tell by the shift in AFR after startup enrichment finishes.

Drove the car again and I think I can describe the issue a little differently/better now. The car actually feels good up until about 2500-3000 in any gear. at that point it feels like I lose a bunch of power and the rpms climb really slowly. Once the rpms reach 3500-4000 it feels like the power suddenly comes back on, and I mean suddenly, almost feels as if theres a switch being flipped, doesn't feel like I'm just "entering the powerband". This makes me feel like something is going on with the knock sensor at around 3000 rpm and its pulling timing. once it exits the "issue zone" rpm wise the timing seems to be no longer pulled and the car runs great.

Is my car actually knocking? My exhaust comes out the hood but I feel like i could still hear the "rattle can" like noise people describe it as. The AFRs show it in 10s and 11s during this time so I'm not lean...

Guess i could unbolt the sensor and let it hang then test.

Last edited by maxitoman007; 07-03-2018 at 06:08 PM..
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Old 07-03-2018, 06:38 PM   #19
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How much was shaved off the head? Or actually, was the head thickness measured?

When the head gets thinned out the slack in the timing belt retards the cam timing.
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Old 07-03-2018, 06:43 PM   #20
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You could be getting a rich misfire at 10:1 of the spark is not hot enough to get a full burn.
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Old 07-03-2018, 06:47 PM   #21
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head was pretty flat when it came off so all I did was gave it a few passes with some medium grit emery cloth on a flat piece of thick mdf. The first time I did the head gasket I ran over it way more times with emery cloth than I did this time and it still ran great with the cam set straight up. I find it hard to believe that the very few passes I made would make such a big difference.

That said, Is there any way to measure the head thickness with the head installed on the car to figure out how much the gear should be advanced? I know the rule of thumb is 1 degree advance for every 0.010" taken off.

Is it possible that the fel-pro head gasket I used is thinner than the elring I used before and that this is causing problems?

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You could be getting a rich misfire at 10:1 of the spark is not hot enough to get a full burn.
Wouldn't I be able to hear that? Im not trying to sound rude, just wondering. I've had the car idling on 3 cylinders and it has a very different sound. When I'm in the "issue range" in the rpms, it still sounds like all 4 cylinders are running to me.
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Old 07-03-2018, 10:59 PM   #22
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A rich misfire is maybe the wrong term, but it can be just a bog and or loss of power from it being to rich. So it can be a bad flat spot in the power band
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Old 07-03-2018, 11:55 PM   #23
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Is this an lh24 car? Did you plug the knock sensor plug in the wrong spot? I know I have mixed the plugs up before and the car did not like that. I recall the IAC and knock sensor plugs being the same, and very close proximity. Usually get a 3-1-4 code or something like that.
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Old 07-04-2018, 04:19 PM   #24
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A rich misfire is maybe the wrong term, but it can be just a bog and or loss of power from it being to rich. So it can be a bad flat spot in the power band
I see, how would one go about fixing this? I'm pretty sure I've leaned out the mixture as much as I can using the adjustment screw on the MAF. I know I could use resistors to vary it further, but I've heard those cause weird changes in the ignition curves. As of right now, when my car enters closed loop, my idle AFR is around 14.4

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Is this an lh24 car? Did you plug the knock sensor plug in the wrong spot? I know I have mixed the plugs up before and the car did not like that. I recall the IAC and knock sensor plugs being the same, and very close proximity. Usually get a 3-1-4 code or something like that.
Forgot to mention the car is a 1987 with LH 2.2
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Old 07-05-2018, 04:23 AM   #25
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Pulled a couple knock sensors off the redblocks in the junkyard today. Time for testing, fingers crossed.
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