msw74

I recently purchased an 87 951 that has a turboS motor from an 89 951. While building speed through the turbo rpm range 3500-5000, the power is not completely smooth. It seems to have slight hesitation, almost "stuttering" through to 5000. Like a slight jerky feeling while the car gains speed.

Also, the car has done twice so far - while powering up to 5000rpm, the power stops all of a sudden. Kind of like if I were to slam on the brakes all of a sudden for a second or two. When it did this, I immediately let off the gas and continued going at a slow pace. I could hear the blow off valve letting off the turbo pressure. So, I drove home after this happened and it seemed to drive just fine, but I didn't push it over 3500rpm. The instance this happened, it scared the crap out of me - I thought I broke something, but when it drove just fine all the way home, it puzzled me.

Could these two issues be related to a plugged fuel filter or failing fuel pump? Has anyone out there experienced this? I am completely new to the 951 world and would like any serious advice available.

djazzy99

I dont know if this helps you, but when i bought my car, it was in bad shape, and it had a hesitation, and a jerking motion as well. turned out the car was missing vacuum lines and had a broken cycling valve among other things. and don't worry, once you get this car fixed, you will be glad you bought it. There are many experts on this board and they will save you a TON of money. good luck!

lart951

Your stuttering might be a indication that you are running lean. The sudden stop sounds like overboost protection, check your cycling valve and your wastegate. When they changed the engine did they replace the DME and KRL?

ehall

Although those things that Lart and Jazzy stated, can cause those symptoms, and you should give them a look, I had that same problem. It did help to change the fuel filter, and it's pretty easy, but that didn't solve the problem. Your mileadge may vary, but check your baterry cables. Check them completely end to end. What was happening to me, with the same symptoms, was that the insulation on the batt. Pos cable was worn through, thus leaving an exposed positive lead. Under hard acceleration, that exposed area would move just enough to create an arc with the closest ground. That caused the whole car to basically skip a beat, if you will. It seemed like fuel stopped for just a split second, but it was the positve arcing to ground.
I presume that the P.O. had the engine work done, so you may very well have the original cable on there. A lot of poeple are going to give you complicated solutions, and they could end up being right, but always start with the really simple stuff first. Though our cars seem a bit complicated, in essence an engine is an engine. Check both battery leads. Jack the front up safely, and chase the positive all the way to the starter. BTW disconnect the battery FIRST, that means the positive. Good luck. There's a starting point.

Charlotte944

MSW:

First off, add your location to your profile so that local owners know where you are and can offer to help.

Second, I would start by verifying that all of the vacuum hoses are good, all of the hose clamps are tight, and you don't have any cracks or holes in the intake J-boot or in any of the couplers between the hard pipes and the intercooler.

Third, what grade of gas are you running? I've had my '86 951 for about 11 months, and for the first couple of months I ran the car on CITGO Premium, but the car runs fine on mid-grade CITGO so that's what I've been running for the last several months. Every once in a while I "treat" it to some 100 octane racing gas and "blow out the pipes."

Using the wrong octane fuel can cause knocking which will cause the KLR to retard spark, which makes the engine run like crap.

Fourth, see if there are any speed/performace shops with a dyno in your area. Putting the car on the dyno can help you find out what is happening. If you cannot find a shop with a dyno, you might be able to do some throuble shooting at a vehicle emissions inspection station.

Fifth, join the PCA (http://www.pca.org) and attend the local chapter's meetings. This will help put you in touch with other owners who can tell you which shops they use and may even hook you up with a 951 owner who can help.

FWIW, I had a similar issue with my '86. The hesitation and missing was not as bad as you describe, but it did happen at about the same RPM ranges that you listed. I found the source of the problem this week end while I was replacing the turbo cooling pump. What I discovered was a loose hose clamp on the line from the J-boot to the hard pipe for the crankcase blow-by off of the oil filler/mist seperator. I'm pretty sure that this hose clamp was causing a boost leak because after I got everything buttoned up I noticed that the boost comes on a tad sooner, and the engine runs smoother that it has in a couple of months.

Finally, welcome to the world of boost!

njim3

If you have boost enhancer with stock chips, you can adjust boost level a little bit lower it should
fix you problem.

Good luck.

msw74

Just thought I'd post some results - thanks for the replies! I tried adjusting the boost enhancer and that did not solve the problem, so I took it completely off and that solved the problem! The boost is much smoother all the way to redline and seems to run much better with no sudden power cut out. Guess it was too constrictive creating too much boost so the overboost protection set in. So, needless to say, I plan to leave the boost enhancer off. Thanks for all your ideas!

WesM951

Hmm, almost sounds as if you where running say 15lbs and the chips where stock chips.

My car acted the same right before the rotor went kaboom in it and took out the cap.

DivineE

Before replacing more expensive parts and spending big money. I would first just try replacing the distributor cap and rotor arm. These are very cheap parts and easy to fit. I had exactly the same problem with an odd hesitation under load and tapping under the engine bay as well. I assumed the worst and started to get very worried. Then someone gave me this advise and luckily it cured the problem straight off. Engine went quiet and acceleration was smooth

Perhaps I was lucky but its got to be worth a try??

Ben

special tool

How did you adjust the LBE?

You will have 5-6 threads VISIBLE for 1 bar.
With stock chips, you must leave approximately 7-8 threads VISIBLE to start with. This will give you 12-13 psi.

Without the LBE, you will be stock boost (11 psi +/-), and not much fun.

DivineE

Worse 9psi!! Its a 220 turbo but I am sorting that little problem I will pm you with a tuning question at some point rather than hyjack this thread

Ben

Evan70

Sounds like overboost protection kicking in. I was experiencing similar problems on my 88 Turbo S. Turned out to be a combination of the Autothority Stage II chips that were in it, and running the stock heat range plug. (Right after I bought the car, and before I figured out it had the Autothority chips, I put in stock heat range NGK Iridium plugs). My final solution, was new chips and one heat range colder plugs, but you might try new plugs by themselves first. I would guess if the PO went so far as to swap engines that he also put in aftermarket chips, so definitely try one range colder. I personally like the NGK-BPR7ES.

As for the hesitation/stuttering at 5000 rpm, I would definitely bet on either ignition or fuel. Unless they've been done recently, I'd go ahead and do the distributor cap and rotor and plugs wires (I already mentioned plugs), and also change the fuel filter. If that doesn't fix it, you might consider changing the coil. After all that, if you've still got the issue, I'd find a dyno with a wideband O2 sensor and do a dyno run to see what the A/F looks like and what the HP curve looks like.

msw74

After I took out the boost enhancer, the stuttering and hesitation went away. I believe it was all related to the boost enhancer. Luckily I took it out before I blew up something expensive! The car pulls strong all the way to redline with no hesitation to speak of at all. I am pleased and need to say that even at stock boost (no boost enhancer), this car is extremely fun to drive!

HansB

If taking away the boost enhancer helps, it seems to me that you are indeed hitting the overboost protection. Get a set of aftermarket chips and you will not recognise your car anymore.

DivineE

That was exactly my problem! However after I removed the boost enhancer the intimitant stutering came back. Thats when I replaced the distributor cap and rotor arm. I think the hessitation you were having sounds an awfull lot like missfiring. The boost enhancer just tends to amplify the fault massively. If the hessitation comes back don't panic. I'm sure your engine will live.

Ben