need help with massive stumble under boost, very long

[russde]

OK, trouble shooting gurus here's the situation:

'86 stock SVO with 145k, ran great until yesterday. Yesterday mirning I started it up and noticed a VERY intermitent miss. I let the car warm up for a few minutes, blipped the throttle to get the idle down to normal, backed it out of the garage, and tried to drive off down the street.
When I attempted to accelerate the car stumbled and almost died. I thought maybe I had just let the clutch out too fast, tried again and got the same result.
As I had to get my daughter to school I pulled the car back in the driveway and took my wifes car. When I got home last night I started the car to warm it up so that I could pull codes....it ran very ragged for a few minutes then smoothed out. I pulled the codes and got only 25 (knock sensor) and 77 (WOT) because I didn't goose it during the dynamic response test.
Since it was idleing better I decided to try a drive. Under normal conditions the car was fine, but under heavy acceleration when it came under boost the engine bucked VIOLENTLY. Like there was an instant of no spark, it literally snapped my head forward. I returnde home and pulled the intercooler off and found that one of the vacuum hoses from the boost control solenoid ( the small round one on the firewall by the air filter housing) was cracked. While replacing the hoses (original) the top of the solenoid came off ( those damn permanent hose clamps are hell to take off). I finished replacing both hoses pushed the solenoid together, put the car together and tried another run....with the same results. A massive stumble under boost, when I had my Merkur I had something similar happen when the hose from the turbo to the throttle body (no intercooler) developed a crack that only opened under boost, but the two hoses on my intercooler are in good shape.
I don't know what else to check. It almost seems that the wastegate is opening completely, instantly under boost when it shouldn't.
Ideas? Help? Advice?
Thanks for anything, and sorry this is so long.
Russ
San Antonio, TX

[SVOtaxi]

Russ,

I had a similar thing happen and it was the turbo/intercooler/throttle body hoses like you described on your Merkur. You couldn't see any cracks or leaks, but I swapped on a set of hoses I had from a spare engine and the problem stopped (for the most part).

Walt

[SVOeric]

you might want to check the fuel pressure..

I would also go over all your ignition componets.

[BigBlue]

90% sure it is the coil. Normal stock replacement at the auto parts store works fine ($25 bux). Don't waste your money on fancy red coils...

Any workshop manual will have the procedure to check the condition of the coil, you only need an ohmmeter. Make sure you read the specification exactly.


Jeremy

[SVOeric]

it could be the coil, but I don't really agree with your statment.

The higher voltage coils do make a difference, and normally are pretty cheap. BTW: i wouldn't get a bright red one either

[BigBlue]

I'd love to see some un-biased results from an average Joe that shows any performance improvement with high-output coils, I really would! If you know of any, please let me know.

[svono50]

Unbiased opinion

Here is my experience with coils on my car. Back in '92 I was running consistent 15.1-15.2 sec 1/4 mile times (still stock except for a K&N & ram air setup). I tried unplugging my knock sensor to see if I would gain anything. My next couple of runs were in the 14.7 range with some slight knocking on each run. Based on some feedback, I decided to get an Accel Super E-coil (the big gray one). I went back to the track and clicked off consistent 14.7's with my KS connected. I tried disconnecting it to see if anything would change...nothing still ran 14.7's but without hearing any knocking.

Based on that info, it was apparent that my stock coil didn't have enough juice to work on my particular car. While a "bigger" coil isn't necessary, it doesn't hurt. If you get a bad tank of gas or one of your plugs starts to foul out, the bigger coil will potentially help until the next weak link in the system is found. If you need to replace your stock coil, why not upgrade? Just my $0.02.

[Mtrain]

My car is doing the samething. It runs fine until you hit the boost. At around 10psi the engine bumps and bucks until I lift off the gas then it resumes as if nothing has happened. I have a new coil, plugs, wires, and ing. module {all stock replacement}. I havent had a chance to check the hoses......mikey

[SVOeric]

could be ignition related, but sounds like you're running lean to me.

Take your car for a 15 minute ride after dark, when you stop, shut the car off, pop the hood, jump out, and see if the exhaust manafold is glowing.
If it is, you are running lean, and probably have a fuel problem.

[russde]

Thanks for all the help and suggestions guys....

I put in/on a new set of plugs, cap and rotor last night and the problem has gone away. The plugs looked pretty nasty (some deposits, mostly white/gray), I probably need to replace the valve stem seals. So...shame on me for waiting too long to replace them.

Thanks,
Russ

[BigBlue]

svono50, I hesitate when I say this, but I think your method of testing is flawed. You went to the track on 2 different days. I've had .8 seconds of difference on 2 different days at the same track, with the same car, running a very consistent automatic tranny. And if you look at the correction factors for dynos, atmospheric conditions matter quite a bit, did you record the barometer readings and temps?

Not saying you did not get a gain from the coil, but you need to isolate all other variables, Did the car weight the same, have the same tire pressure, the same gas? Your knock problem would indicate that you had bad gas on the first time at the track, and a simple fill up with good gas would have eliminated the knock and caused you to get a 14.7 the first time out...

Glad to hear you found your problem russude