4age Blacktop swap, bogging / hesitating badly

[gjgnz]

Car: KE70
Engine: 4age blacktop 20V, bought as a complete runner from an importer
ECU: Standard (Auto)
Ignition: SQ Engineering Distributor relocation kit
Fuel pump: Lift pump, surge tank, Bosch EFI pump, new lines and filter

Problem: Engine starts and idles fine but bogs badly when the throttle is applied. Will rev OK if throttle is applied slowly.

Already checked: Cam timing OK, ignition timing OK (10 degrees BTDC), no fault codes on ECU. Pulled plug off TPS and the idle jumped up slightly but otherwise not much difference. Pulled plug off MAP sensor and engine wanted to die. After doing this I got fault codes for both sensors, as expected.

Any suggestions?

[davew7]

Borrow a VOM then check the TPS per manual. I would also verify the wiring from the TPS to the ECU and check fuel pressure.
Dave

[hayashi]

I had a similar issue. Faulty / incorrect knock sensor installed. Swapped it for a new one and the bogging dissapeared. Another thing that can cause hesitation is the VVT pulley.

[Matt]

There are a number of things as the guys have said. I have experienced the knock sensor myself on a couple of occasions. Leaky capacitors in the ecu is another common one.

Have you given the car a chance to warm up? My daily has a faulty temp sensor which causes it to big down until I've driven about a km. It's worse in winter than summer.

02 sensor or missing sta signal from the ecu won't cause it. Speed sensor input missing from the ecu also retards the timing a lil and will drop the rev limit but won't cause it to bog down.

[Sam-Q]

Make sure that there isn't any vacuum leaks, spraying soe engine start spray around the throttles would help determine that. If the revs go up then it's sucking it in somewhere.

The MAP and TPS sensors can both cause these issues. The TPS sensors however are much more known to wear out and need replacing. But make sure that the MAP sensor rubber line doesn't have any cracks or similar.

I have TPS sensors in stock but no knock sensors, but by memory I added some to my last order and they should be here in about a week. I should also start to stock MAP sensors seeing this isn't the first time that someone may of needed one.

[tuned86]

Could also be clogged injectors not opening which would explain idle and rev slowly. Typical problem if the engine has been sitting around for a long time...just have to check bit by bit until you find it...

[Futo_gt86]

I had a Silvertop do the same kind of thing to me.
Does the Blacktop have same Idle Speed Control Valve as Silvertop?
If yes, might want to check out how ISCV is plumbed.
I deleted mine altogether which made the symptoms disappear, opened up the top end and wide open throttle.
I had aftermarket ECU so I could tinker with the idle to get it right, not sure how Stock ECU would react.
Good luck with it and let us know how you get on with this issue.

[Matt]

It will throw a check engine light if it is unplugged , I had a high idle issue years ago which turned out to be a stuck valve.

Carby cleaner usually un-sticks these.

[gjgnz]

Finally got around to looking at the car again today:

TPS resistance is in spec and wiring to ECU is all intact
Sprayed ether all around intake and no obvious vacuum leaks. All vacuum lines are new.
Knock sensor is connected but have no way of testing it.
Pulled ECU apart and all looks fine (no leaky capacitors)
Unable to check fuel pressure as I don't have a gauge but both fuel pumps and lines are brand new, wired and plumbed correctly. FPR is factory and untouched. What would be potential causes of fuel pressure issues?
Car idles really high with ISCV disconnected, much better with it on.
When I was messing around with the dizzy it definitely seemed more responsive when the timing was advanced.
Also noticed there is a lot of carbon buildup in the intake manifold behind the throttle plate. Car has backfired out the intake on previous starts. Is this anything to be worried about?

[Matt]

Check the condition of the dizzy cap, the carbon pile can wear out over time.

[tuned86]

Sounds like you are running out of things to check... For electronics, you can use a multimeter and download the Blacktop FSM which will show you how to diagnosis sensor equipment and check they are within specs.

Confirm wiring is done properly? Maybe the Injectors are getting constant ground and not grounded by ECU through #1, #2, #3, #4?

[greeneyes]

I have the same problem on my 16valve, but only when hot. Occasionally the idle drops and it will stall if not held up by the accelerator, and it just dies if I try to driveaway. It runs fine when cold or warming up. I have my mixture display hooked up and it leans out when idling (as normal) but doesn't richen back up to drive away.

I took the fuel return line off and ran it into a bottle to check if it had fuel pressure in the rail, as it just feels like it has run out of fuel, & I was surprised how much flowed out in a few seconds. I figure if you do that it means there is plenty of fuel available for the motor to rev.

I figure it could be the TPS, maybe the fuel delivery to the main pump, maybe the oxy sensor. ..and the Toyota advice of last resort, 'try another ECU'..

If it was an air leak the ECU would compensate for it via the oxy sensor and the idle would go up. Does the 20valve have the vac line on the fpr that acts as an accelerator pump to get it reving?

[tuned86]

Finished my swap as well and I have a very similar problem after I worked out all the kinks...

Here are my symptoms:
* Disconnected VVT - drives nicely very smooth etc
* Connected VVT - Bogs WOT under 2500 causes blogging...feels like turbo spool...really this shouldn't be happening for a NA, VVT or not!

Car does feel alot more potent with VVT on but it just doesn't drive smoothly. I am suspecting it must be the VVT gear itself then in that its crapping itself on engagement? Problem is VVT disconnected everything runs smoothly which means my sensors should be in take and Base timing set to 10deg.

Checked
* TPS
* ISCV
* STA wiring
* O2 Sensor
* ECU Caps & VVT Transitor

[gjgnz]

I’ve tried disconnecting the VVT but there was no noticeable difference in throttle response. There are a few things that are really bugging me at the moment:


Firing order. With the SQ distributor kit the leads should be connected 1-2-4-3 on the cap. My engine will only run if it’s hooked up 3-1-2-4 (i.e. cylinder 1 hooked to post 3, 3 to 1, 2 to 4 and 4 to 2).
Ignition Timing. The timing is set to 10° BTDC with the check connector bridged. When I accelerate slowly the timing advances but if I hit the throttle suddenly the timing retards momentarily, then advances. The only thing that made any improvement to throttle response was advancing the timing.
Intake backfire. The car will often backfire out the ITBs, particularly if you rev it, come off the accelerator, then get back on it. It’s a sharp white-blue flame, almost like a big electrical spark, not a slow orange fuel flame.

[LittleRedSpirit]

Intake backfire makes me think you're 360 degrees out of phase with your cam timing 720 cycle or firing order perhaps igniting on the exhaust stroke instead of the compression stroke or something. On my setup the only time I saw this was when i working out the correct triggering phase and was igniting things out of phase and firing order.

[LittleRedSpirit]

and your firing order would seem to support this as it should fire 1342 stock and sam qs kit probably wont change that. With your 3124 you are cylinder swapped within phases compared to stock if you catch my drift. Maybe Im confused.:yeah:

[gjgnz]

With the SQ kit the rotor effectively spins in reverse so the order on the cap becomes 1-2-4-3 to achieve a 1-3-4-2 firing order (i.e. leads 2 and 3 are swapped). On my setup, with the motor at TDC on cylinder 1 the rotor points at the post for cylinder 3 (i.e. swapped lead 1 with 3 and lead 2 with 4).

I've re-checked the timing marks three times and everything is where it should be. I definitely didn't spin the crank a full rotation when I changed the timing belt either.

The strange thing is that it starts and idles perfectly, it only gives any sign of a problem under sudden throttle. Did yours backfire when it was running or only when you were trying to get it started?

[LittleRedSpirit]

Mine never back fires now its tuned and running unless my tps frags out from a ground loop im chasing and gives me a puff of fuel I dont want on decel or I have the transient enrich too high and when I back off there is unburnt fuel to explode in the exhaust.

If its just at low rpm maybe you're throttles are badly out of sync. Have you ever downloaded the manual and checked their adjustment with the feeler gauges, I did recently and it was a revelation about how nice and low a motor could idle down low and pull from low rpm with itbs. Get your hands on some sync gauges and see ho much vacuum each port has. Pull your plugs if they have uneven air available then one might be foulded while another looks lean while another looks normal.

Otherwise if its only happening at low revs when you give it some decent throttle then those are the conditions that a 20v should be applying the vvt advance, so your test with and without vvt becomes compelling.

Does the rotor button only go in one way? maybe its backwards? Spinning backwards to the norm is one thing but starting on cylinder three is odd even if it spins the other way, surely it would still start at one and go 1243 like you say?

[gjgnz]

Made some progress today. It turns out it is possible to install the dizzy kit incorrectly by putting the locating pins in the wrong slot in the cam gear:

http://uploads.tapatalk-cdn.com/20160709/8c261761781f696f213f8341a444b031.jpg

Effectively the rotor was about 120 degrees off where it should be. I've fixed that and the firing order is now as it should be.

The car seems to run a bit better now but it's still got a decent hesitation and can feel like it wants to die if you give it WOT. No difference with or without VVT connected.

[tuned86]

I had hesitation from Low rpm to 2-3000 RPM if I was on WOT.

It was fixed after I tried a few things but I suspect the biggest culprit was running open trumpets - too much air at low rpm caused hesitation.
Things I did:

* Install pendulum (was getting RWC at the time)
* Cleaned OCV
* Ran the car for awhile so ECU could learn/trim

I'll be able to confirm this the exact cause later. Anyone else have problems running open trumpets using stock ECU?

[Matt]

Open trumpets are fine.

If you run the stock black rubber trumpets without the plenum it is actually significantly slower.