ttAmerica RoadsterAWD

So, my 1988 turbo decided to start bucking hard when gently accelerating (getting on the freeway ramp). It feels like the fuel was being cut off and the engine would buck and pull back. No backfires, just felt like fuel was sporadically cut off. Idle was ok. I took a look under the hood and discovered a split/crack at the vacuum line on the diverter valve (blow off valve). These are new silicone jobs from LR. I was surprised because silicone is suppose to be strong....

Anyway, I was trying to understand how this could cut off fuel, but then I see it plugs into the fuel regulator directly. this has gotta be the problem right? It just seemed to do this when the ambient temperature was hot. Seemed to be ok at night when its cold, but maybe I'm not understanding it and maybe, just maybe it was the split at the diverter valve

what do you think? Do I have this right?

jaime

Dan Martinic

I don't know if the break at your BOV is to blame for your issue, but I highly recommend you read this https://rennlist.com/forums/944-turb...her-stuff.html , contact Laust, and see if you can get one. This is how it looks installed:

Humboldtgrin

That vacuum hose routing dosn’t sound right at all. And silicon vacuum lines are weak and easy to slice.

ttAmerica RoadsterAWD

Ok. Hose material aside, does this explain what could happen? Does a split introducing air into the regulator cause fuel cutoff??

Humboldtgrin

My apologies. I was thinking wastegate not blow off valve. You may have bad spark plug wires or a dying coil.

ttAmerica RoadsterAWD

Ok. That’s a good suggestion. I will replace coil, wires, cap and rotor.
Thanx bud!👍🏽

Willard Bridgham 3

Check all your pressurized hoses/connections after the turbo. Do a pressure test.

GPA951s

Mine does that every year... the first time I take it out in the spring (Because of old Gas) I just chalked it up to a "Ping" and Run the old gas out fresh 93 and no issues.. Its a Ritual...

Tom M'Guinn

The FPR needs a good vacuum/boost line to manage fuel pressure, so it is "possible" the broken line downstream of the FPR caused the fuel pressure to be too low under boost and created the sense of fuel cut off. That said, more often than not, what you describe is caused by weak ignition -- cap, rotor, plugs and wires.

951North

Does it happen at any particular boost level? say 1.5 bar? see my thread about a misfire issue I was having... It was improperly gapped spark plugs.

ekoz

I had the issue....started messing with fuel stuff...new regulator, etc....had wife start it to check for leaks....immediately noticed spark plug wire jumping to ground. Only did this on certain turns and speeds when wire would "lean" a little

kev951

bucking can usually be a sign of your speed and reference sensors going bad and or their connectors or ignition coil..... Losing your spark basically.

ttAmerica RoadsterAWD

Hey guys thanks for the info provided. Today I replaced the coil with LR "upgraded" coil, all new Bosch rotor/cap/, Beru wires, new properly gapped (0.7mm) spark plugs....... and still seems to go into limp mode, but I've done some observations:

When in stop and go traffic, and ambient temperature is in mid 90's, and the engine bay gets hot is when I have the problem: engine seems to get weak (timing is retarded?), starts to go into an overboost protection (I think), when getting on the go pedal after waiting on a red light, my 1st gear feels anemic, then while on second gear my boost gauge starts to read 1 bar the engine cuts off, spudders, bucks and farts too, seems the fuel is being cut out. As my engine vacuum approaches the 1 bar (stock boost gauge) my engine starts to bitch at me..... dammit!!


BUT, then in the evening when temperature goes down to the mid 70's, damn car pulls like a train all night long! Drove it all night til I was bored. I am not able to reproduce the problem when its cool outdoors.

Seems it's a temperature thing! What could it be??? This is bizarre!!

Dan Martinic

The AFM sends a signal based on flap angle & temperature. I forget if you've tested it

Tom M'Guinn

You might check for blink codes at the diagnostic port under the hood (excess knock when hot?). See clarks and/or many threads on that here. Intermittent problems are the worst, but sounds like you at least have a pattern of sorts. Electronic things and electro-mechanical things can fail when hot -- cracked solder joints in DME/KLR, fuel pump, injectors, AFM, etc. Do you have any way to log data while driving?