problem at full throttle

[five-0]

Hi everyone. I am a brand new owner of a 87 turbo and I have a question.

At full throttle, the engine bogs down and surges-like it hits a wall. But, if I ease up about an inch it takes off like a rocket, full boost all the way to redline. It's like a dead spot. No other issues at all except that one spot in the throttle. Help please.

[Fast951]

Few things to check/test:

- TPS (high possibility)
- If running stock AFM. Remove black plastic cover, notice any damage to the film under the wiper.
- Check all the hoses on the pressure side of the turbo
- Measure the exact boost, make sure you are not hitting overboost protection.
- Is the car going lean or rich when it surges?

[five-0]

Thanks for your input. Since I have never owned one of these cars before I pretty much know nothing. Although I did suspect the TPS or AFM. I'm just so unknowledgeable at this stage I am hoping someone can help me. As far as lean or rich I'm not sure how to tell. It's not smoking or smelling funny. I don't think it's overboost protection because I can be at low rpms and little boost. Then when I put my foot to the floor it just starts bogging down before boost even starts climbing. If I never put the pedal to the floor I'd never know it had a problem because it's normal at all other throttle positions.

[jeff1hughes]

five-0, welcome to Pelican, you will find this is a very helpful place. There is one thing you forgot though, when you're new you have to post a picture so we can all enjoy your new ride! Good luck!

[alex_cristocea]

i have the same problem with my 87/951, but mine it's a little different. If i kick down the throttle 1st redline(approx 80km\h), 2-redline(approx 140km\h), the car boosts all the way to red line, but in 3-rd gear at 5000-5500 rpm it's starting to lose power and if i keep te throttle down at around 200km\h the engine stops like it hits a wall, it's not just decelerating, that is with the sport driving.when I drive the car normal the problem it's different: 5-ft gear 100km\h ~2000rpm i push the throttle down it's accelerating but when i hit the 180 the engine stops again, that it's just for the first or second attempt because, after that, i have the same problem at slower speeds.I also have to mention that after the engine "hits the wall" if i press the clutch engine stops and can be restarted with no problem.
Another fact that I have to mention is that that if i ease down the throttle just a bit the car just fly and is going past 260km/h with no problem.
I think the problem it's with the boost because a few days ago I was in the second gear @3000rpm I pushed the brake an the throttle at the same tI'me, and when the boost indicator was around 1,9 bar - the engine has stooped again.
The car has this problem since I brought it and since I'm living in Romania i have no specialized service or even someone who could give me an advice.I think the problem it's the over boost protection but I'm not sure and i think the wastegate it's modified, also the fuel damper doesn't have the vacuum plugged I'm, i have put in one but with no result.
If you hve any ideea about how can i fix this, give an answer pls.
Thx.

[five-0]

Thanks for the welcome and the input guys. Alex, I will definately let you know if I get this solved. I think it's going to be a long process of checking many things. Which I guess isn't all bad. At least the car is driveable, and I will learn a lot about it through the troubleshooting process. I'll keep you posted.

Jeff, I will post pics soon. I haven't got around to taking any. She needs a bath, wax, hood repaint. So it's not pretty now. I'll post the pics when i get it cleaned up this week. 87 Guards red/black interior BTW.

[nize]

it could also be a faulty cycle valve.

[alex_cristocea]

You have any ideea how can i perfrme a test or how can i check if the valve is ok or not.

[nize]

it's very difficult (at least i haven't been able to figure it out) to accurately test the proper electrical operation of the cycle valve. there are a few ways to test via indirect means though.

1) clamp the wastegate line between the cv and the wastegate using a mini vise-grip. what this will do is keep the wastegate shut regardless if the cv is failing or not. then you can test if the motor still bogs down at full throttle.

WARNING: your boost will spike (and continue to build) so be VERY CAREFUL on the throttle or you will blow your motor during this test.

2) replace the cv with a known good one and see if the problem goes away. it's a major pain to get to the cv without removing the intake headers though, so this is a pain to do. i was actually able to do it by using a 90-degree bent allen wrench but i have not heard of anyone else who was able to with the intake headers in place. while you're doing this, be careful you don't break/cut/crimp any of the small vacuum lines! they're usually so dried out from the heat that they're brittle.

[alex_cristocea]

ok
ok man.Thanks for the advice.I will try this week end and see if there is a difference. I forgot to mention something i have seen on the engine since when i brought the car.
1. the fuel presure damper doesn't have a vacuum line plugged in.
2. In the picture above the line witch is marked with red has an on/off switch, witch was off since i brought the car. I turned on few days ago and first time i tried the enegine did not bog at the first time, but at the second attempt i had the problem again.(the picture it;s from the internet, it's not my car).This week-end i plan to change the timing belt, the balance shaft belt,the transmission oil and if I'll make some picture i will post them.

[nize]

that rubber hose that comes off the banjo bolt (circled in your photo) ends up as one of the three hoses that connect to the cycle valve. that hose is important because it controls the wastegate. if it has an on/off switch it seems someone was playing with the boost. i would not advise turning that off, as your boost will spike and you'll damage the motor.

do you know what modifications were done to the motor?

[alex_cristocea]

i don't know if there are some other mods on the engine.I think there is a chip tuning because when i change gears at high rpm some fire is coming out on exhaust, some black smoke(i know whats is happening bun i don't know how to tel you in English ). the car accelerates like mad is beater then other 944 i have ever drove. few months ago i smoke an m3 (2000 or 2001).All i want for the moment is bring it back to stock because the engine parts are very expensive in romania.The ex owner told me that some back yard mechanic made some modifications on the waste gate spring.Now I'm thinking to buy an custom waste gate but i don't know where i can find one.The timing belt i had to order it from UK.
......I have a lot to work

[nize]

it sounds like the car may have been abused by over-boosting. if you don't know the complete mods that have been done, you should go through it all and find out before you start troubleshooting.

i'm assuming the stock boost gauge goes up to the max 2bar so you don't know how much it goes beyond that. do you have an aftermarket boost gauge? you should MAKE SURE you are not overboosting before you get on the throttle again. i'd hate to see you destroy the motor and find out the hard way why so many of these cars end up being sold for cheap.

[alex_cristocea]

You are right man.That is why I'm trying to solve this problem.And i have started this in January.Since then i learned a lot allot about this car.The most usefully part is this forum and the service manual witch i found on the net.I tryed to watch the boost gauge but i don't think is working well because with engine stooped and with the ignition switch turned on the second position the boost gauge indicates 0,9(i think 1 is the normal atmospheric pressure that it should indicate).I have seen that the engine bogs down below 2 bar.I don't think the reading si accurate but since i don't have an additional gauge i have to take it as good.

[alex_cristocea]

i have one more question. if is an over boost problem why does it not bogs when accelerating on a straight line.It hits 200 km\h with no problem, but when is at km\h normally down the road if the throttle is pushed to the floor the engine surges.I think i will find this only after when i will diagnose all the parts involved.

[nize]

1) find out all of the mods that have been done to the car.
2) get an aftermarket boost gauge and make sure you are not overboosting.

you can get one for very cheap here;
http://www.egauges.com/vdo_mult.asp?Type=Turbo_Boost&Series=Vision&Cart=
the 0-30 In.Hg. to 0-25 PSI for $30 is the most popular one.

any troubleshooting done without knowing exactly what mods are on the car is pointless and dangerous.

[five-0]

Just to add to this, the car has 15psi guru chips, accuboost controller, 3.0 Bar FPR, Tial 38mm wastegate.

Something I found on Rennlist is that several people with this similar problem had a bad plug wire-like melted. I will check that tonight. I haven't even had time to begin looking at this yet. But yeah, I need some good gauges to start with.

[nize]

here's another possibility that occurred to me recently; you could have faulty injectors.

when was the last time the injectors were cleaned and flow matched?

[five-0]

I dunno, I just got it recently. I'll look into it though. They are original injectors. Thanks for the input.

[alex_cristocea]

Today I was at a service to change my timing belt and balance shaft belt.So here it is what i found wrong inside:
1. The intake bot has some holes in it so large that you can see inside.
2. The balance shaft belt was not there.It was MISSING.
3.The balshaft tensioner and the balshaft smooth roller missing.
4.The bypass air valve was not OK.
5. when engine at TDC the camshaft mark was 180 degrees deviated.
I have patched the intake boot and I did not experienced that problem that i had at the full throttle.(I'm not sure it is solved because I was in town and I did not pass 180km/h.)Any way i have seen that the boot is stronger with the throttle at 50-70% then 100% pushed.
Tomorrow I Will start loOKing for the parts missing. I hope I can found them here in Romania.