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I have a recently acquired 87 turbo with zero records and little info on it. I'm going through and have been catching up on maintenance and am to the point of deciding on direction for the car.
Soon after putting it back on the road I would get an intermittent boost cut at higher boost and loading in 4th or 5th gear. It's progressed now to where I can replicate the condition in 2nd gear and up.
I've installed an autometer boost gauge to help identify the issue, T'd into the boost signal hose at the KLR.
When the misfire occurs, there is generous throttle input and boost is upwards of 7-8 psi. Prior to the issue causing drivability issues (it would do it occasionally before, now it does it every time) I would see a peak boost of 15 psi in 5th gear.
The car was essentially stock why I received it with the PO telling me that the drivetrain was from an 89 S.
Stock exhaust (with cat)
26/8
Stock WG and doesn't appear to be shimmed.
When I opened the DME and KLR today for inventory, the DME chip is a 24 pin stock numbered chip and the KLR chip is aftermarket and something I haven't been able to identify.
When the misfire happens, the tach drops to zero momentarily (as long as my foot is on the throttle) and the car lurches and backfires through the exhaust.
I've recently completed the following:
Belts, rollers, water pump
Vacuum lines replaces with silicone.
Throttle body cleaned and couplers from the IC cleaned and sealed.
Cap and rotor.
There was no notable oil in the IC pipes or TB.
The car starts and idles well and pulls 15-16" WC of vacuum at idle (approx 900 rpm).
Questions:
What are the likely causes of the misfiring?
Is it possible for the car to not be lean on boost with just a KLR chip?
I have a blink code tester from Arnworx and have verified it works; why would I not get any codes when I follow the direction for connection and use?
I am considering going the VEMs route for engine management but concerned that it uses all the factory sensors and harness, anyone with experience?
Thanks, sure does sound like the TPS reading the Clark's diagnostic procedure. In the interim, I just disconnected the TPS to check. With it disconnected, the stumble at idle is gone (it idles at 1400-1500 rpm disconnected) but the boost cut and back fire is still there. I'm going to go through the clark's garage test protocol to measure actual function.
It also occurred to me that when the car is first started, it is more "drivable", not exhibiting the same hesitation except around 2500-2700 rpm, granted I'm not driving the car hard while the oil is cold. It made me think about the O2 sensor and if the car is running a version of open loop until the o2 sensor reaches temperature. It seems rather dramatic a result for a bad o2 sensor though.
Willing myself to not just throw parts at it.
Last edited by Northern_aqs; 11-20-2015 at 07:38 PM.
Sounds just like what my car was doing, get a smoke test with pressure you may have a boost leak. mine was the intercooler to throttle body boot .almost invisible split that would only open up under boost. took two smoke tests and a lot of head scratching to figure it out
....87 turbo......intermittent boost cut at higher boost and loading in 4th or 5th gear. .... I would see a peak boost of 15 psi in 5th gear....26/8....the DME chip is a 24 pin stock numbered chip and the KLR chip is aftermarket...
Any reason you do not suspect this is the overboost protection kicking in?
Any reason you do not suspect this is the overboost protection kicking in?
My feeling after further investigation is that there are two issues at play and yes one being overboost protection with one caveat: when I initially received the car and after performing the belt change, the car would boost to 15 psi (in 5th) without issue whereas now the car (when warm) will now buck and backfire at 7 or 8 psi. The car initially began to do this occasionally in specific circumstances in 4th or 5th and now does it consistently in 2nd through 5th.
The aftermarket chip (of unknown specification) in the KLR was at some point supportive of the additional boost where now it isn't.
On further inspection of the intercooler pipes and couplers, there are no cracks save for a potential mark on one of the elbows on the diverter valve. I don't suspect a boost leak ...currently.
After the car completely cools, it starts and idles smoothly, until it warms up (granted that takes a while in the 1 degree celcius weather we now have).
I had hoped to resolve the issue before pulling it apart for motor mounts, rod bearing, waste gate and exhaust work but I suspect there is some crusty wiring providing some of the problem. The car had only been driven 14k miles in 15 years (primarily as a track DE toy) before I bought it, me adding 2k miles in 6 weeks may have exposed some worn out, dried out parts.
I'm planning on ordering the reference sensor harness and injector harness from Lindsey Racing, however I'm not clear on how it's connected at the DME and KLR; I can do a lot of things, but soldering isn't one of them and wading in ham-fisted and making more problems is not something I'd like to do. Anyone with experience? The TPS tests fine with it cold, I'm thinking either the sensor or its wiring goes bad when it gets heated up and expands. No way to really test the theory easily right now, so I'll replace the harness and pray. Thanks for all the replies.
My guess is you have a few things going on. The AFM could contribute to the type of symptoms you have described. does the car still have the cycling valve or manual or electronic boost controller? I would also do what you can to identify the chip as this will tell you what boost limit is set to. or better yet replace it with something that you know will work for your setup.
I'm not a guru, but I had a similar problem many years ago where I can only assume the Boost Protection was kicking in as the boost came off so violently it was like the brakes slammed on. I went the cheap route and started replacing all my vacuum lines with Lindsey silicone first as a test. It ended up going away after I replaced one that was under the airbox.
I also had a shunting Idle too and traced that to a leak in the boot to the throttle body, and another time a rip in the J-Boot.
I had similar issues with my last build first it was the AFM then the TPS blew out the side so I rebuilt the throttle body and replaced the TPS. I then added a adjustable FPR and Lindsey chips and it is great but still has the popping in 4th and 5th when accelerating hard. I have a manual boost controller and recently turned it down since the weather is bad and I noticed the popping out the exhaust is worse. I would like to shim the waste gate or replace it with a dual port and an electronic boost controller and the issue should be gone.
You may have installed the timing belt one tooth off. Read Clarks garage on how to do the timing belt on a turbo. It's different then the regular 944 which you should line up all the timing marks. The cam should be advanced. Or as I have seen stated the crankshaft should be retarded 1.5 teeth (same thing). Or the cartylitic converter melted like mine did, but that was at 21 psi so I dought that.
interesting... I will look into that. I have Lindsey 3 inch with no cat so I know it is not restricted. I will try advancing the cam timing this weekend ad report back.
Sorry northern I don't mean to hijack your thread.
The stock overboost is setup to kick in if the engine load (Air flow / RPM) was above a preset value (load limit, RPM based) for a certain period of time.
If your AFM is OFF (reading higher than it should), the boost is higher than stock causing higher air flow. Or the chip does not have a raised load limit, then you could be hitting the overboost. Overboost works as a fuel cut! This is part of the DME.
If using the stock cycling valve with the KLR for boost control, then it's possible that the DME & KLR chips are not in sync. (KLR commanding higher boost, but DME is not programmed to handle it).
If your car is kicking and firing once you hit 6-7psi, then something else is the cause. More than likely you have a pressure leak (air escaping the intake after the turbo). And/Or you could have failing ignition system. A bad TPS could cause similar behavior.
I would start by pressure testing the intake system. Then go from there.
I think that first video is your best clue. The tach runs off the same signal that runs the motor, and you are clearly losing your ignition/tach signal when the car is cutting out. The motor is not slowing and restarting that that quickly (it can't) but rather the ignition is just cutting out causing the tach to cut out briefly. The video also shows that your KLR is not losing electrical power when the tach cuts out, because the boost gauge retains power, so that probably rules out a bad DME relay and that sort of thing. Have you tried wiggling the speed and ref sensor connectors to see if that creates any issues -- if so, that could be it. If not, then you might have a short in a harness that's shorting out the ignition signal, or a cracked solder joint in the DME or KLR, or a coil or ignition driver going bad. Might start by putting a scope on the ignition signal and see what's happening to it when the tach cuts out...
11-20-2015, 02:26 PM
Boost cut, backfire and chips
