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Thread: Infuriatingly Mysterious Lack of Oomph (Power) Reply to Thread
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  Topic Review (Newest First)
05-08-2019 07:25 AM
1stgenxxx Shew....Sound like it needs an LS swap!
03-07-2019 01:23 PM
bronzeking Check for a vacuum leak. and the vacuum line tee, in front of plenum, and the vac line to the fuel regulator. also the big Vacuum line behind the plenum for leaks. I use propane to find vacuum leaks ...clogged or blocked muffler/tail pipe..incorrect ignition timing.. The distributor could be 180 degrees off as well.. vacuum advance perforated or the line leaking to it, .. My ignition wires go bad every year also..what is the idle rpm? I run the pertronix dist. fixed a number of problems I had..clogged fuel filter or bad fuel pump will show correct pressure at fuel rail, but cant deliver enough fuel under load..hope you solve it.. and yes I almost forgot..temp sending unit in intake manifold, and the final weird thing it could be what is your coolant level? two hoses run to place under plenum intake area. if coolant is low,,or NOT VENTED properly on filling it will never run correctly. read about adjusting the TPS, in forum or at atlantic british web site . need volt meter.
02-28-2019 02:11 PM
mikieman The slight stall when reving is normal
I knew a guy who had a similar problem
I thought it was clogged cats
But it turned out to be the tps causing
His problem
He replaced it and got his power back
02-28-2019 11:39 AM
LanceL I was wondering about the TPS, it revs smoothly, but very slowly. What would be the symptoms of a blockage, and by that do you mean cats? If I just twist the butterfly on the throttle body it revs up, but the response is very delayed. I can blip the throttle (by hand) and it doesn't really leave idle. It takes a solid 1-2 seconds before it responds to the throttle opening, and it revs very slowly. When opening the butterfly wide open from idle in neutral, it takes about 4-5 seconds to go from idle to (near) redline.
02-25-2019 03:49 PM
mikieman It has the sound of some kind of blockage
Could also be the tps
When it at idle
Will it rev good
02-25-2019 10:32 AM
LanceL Kickdown cable seems to be fine, if I bury my foot it drops a gear and winds up, it just doesn't go anywhere. More noise, no more movement.
02-22-2019 07:20 AM
mikieman Going out on a limb here
Have you checked your kick down cable
It’s a good lead
02-21-2019 04:28 PM
LanceL Gratuitous glamour shot attached to garner some extra sympathy.
02-21-2019 03:27 PM
LanceL I don't think it's tooth off, I tried to make sure the marks were perfectly aligned when putting it back together, but I suppose it's not out of the question. However, the power isn't shifted to the higher part of the rev range, it seems to be and extremely flat curve, with no real difference at all in grunt when pulling from 2K all the way to 4.5K. It makes a lot of noise, but there's no change in power. It doesn't feel sluggish immediately off the line, but it feels like whatever oomph it's got at 2K is all it's got for the whole rest of the rev range.
02-17-2019 01:09 PM
Kevnic Are you sure you are not a tooth retarded on valve timing? Assuming everything went back together correctly with the cam swap... A tooth off would shift the power high in the Rev range(not give any more)
Low end torque would be pitiful, well worse than stock let's say
02-17-2019 07:39 AM
Updates for those interested

Gents, a few updates since the last time this thread was alive. I discovered my EFI light problem was O2's, so both are now shiny new. Cleaned and tested the MAF and it appears in good working order, but she's still as slow as ever. Had a good demonstration of how slow last week, when I helped a friend move a small uhaul box trailer. Now RRC's are supposed to be able to tow 4500lbs in high range, and 7700lbs in low. This was approximately a 2500-3000lb trailer, so not unreasonable, yet on a number of hills (not that steep mind you, these are normal 45mph roads) I was in first gear with my foot buried to the floor trying my absolute best not to completely grind to a halt. 0-40 on flat ground took close to a solid minute, winding all the way to 4k+ in all gears to make any headway. We had the hazards on out of necessity the whole way and pissed off a lot of impatient people.

Now the above embarrassment prompted a compression test, which I hadn't done with the new cam (or in a while actually). When I last did one (about 2 years ago), the results ranged from 145 as the highest, averaged about 137-138, and a single low at 123 (mind you this was on a slightly warm engine). From what I understand, on a hot motor the 8.13:1 compression should yield between 150-160 on a perfect motor, so I thought ~140 on a 135K motor wasn't too bad. Fast forward to yesterday and a subsequent compression test. This was on a warm (not scalding hot) motor, with a new more aggressive cam (bit lope-y sounding, so some mild overlap at idle), and my wife cranking the car while I looked glumly at the gauge.

1: 120
3: 108
5: 112

4: 110
6: 110
8: 120

Now this seems dismally low, which would signal the need for a rebuild, but it just seems odd since it runs so cleanly, doesn't burn a drop of oil (or coolant), and passes smog (in CA) with flying colors. Is it just tired, despite all that, or am I missing something? Basically at this point I'm just desperately trying to avoid a $5K+ motor rebuild, or crate motor drop in. Thoughts?
01-09-2019 04:20 PM
LanceL I have one new (less than 5k miles) cat and one old one, I asked the guys at my exhaust shop what they thought about the cat since I was curious about exactly what you mentioned, but they seemed to think that since it still passes smog just fine it shouldn't be an issue. I wish there was an easier way to check than having to unbolt it, I'm terrified of snapping one of those ancient rusty exhaust flange bolts.
12-12-2018 05:16 PM
Harley 86 I might be too late on this but... have you checked the catalytic convertor? It can be starting to collapse inside. You can Disconnect unbolt it tie it up and then drive it.
12-04-2018 03:41 AM
p76rangie Before replacing the fuel pump, check the connection on the wiring plug at the fuel pump.
12-03-2018 02:30 PM
lufc12345 It is interesting to read your post as I have had similarly frustrating issues with my 3.9 (1995). I have replaced a fair bit under the bonnet (all ignition, O2 sensors, air filer, earth points.....). I have just started to get the same lack of power and hesitations (only slight at speed, hills are a killer) and i got the Check Engine light. The fault was fuel supply and i am leaning towards ordering a new fuel pump.

This is frustrating as i only put a new fuel pump on 2-3,000 miles ago but it was a Britpart pump and I wish that I had put a better quality unit on! I thought that i would mention the fuel pump as I didn't see it listed and they tend to go over time.
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