And now, how to cure the "hiccup" at high boost?

[mutungi]

When accelerating uphill, at kickdown or at sudden acceleration at high speed on motorway to increase speed, the car "hiccups" (cuts-out) and resumes normally if you release the gas. Have tried new DI unit, new NGK's gapped at 1.0mm but problem still there!

[pete_turier]

Ooh! Sounds like the overboost protection is coming in.
What boost levels are you running?
Pete.

[SAABPILOT]

Had a similar problem once on a 2.0LPT Bosch LH Saab DI system, turned out to be the Inlet Air Temp sensor (half way up the inlet trunking)

[mutungi]

Boost levels? Default from factory....I have not adjusted anything....this is a LPT...can it be adjusted? How do you check/determine the boost levels?
Inlet ait temp sensor? Is this the brass plug screwed in the inlet manifold with the black wiring harness?

[Matt Atkinson]

Check the waste gate operation rod hasnt corroded through and stuck open. Took me ages to find on mine !!!!!. It gave identical symptoms!

Matt

[mutungi]

Well.....gave it the true test on the way to and back from Wales yesterday, afraid it "hiccups" with sudden acceleration when overtaking or going uphill when more power is required....no "hiccups" when you increase speed gently. Plugs set at 1.00mm (NGK's), all hoses,etc Ok......is there a boost protection somewhere which is set low, etc. or ....???

[9000CS23T]

Definately sounds like overboost protection working. I take it yours is FPT if so watch your boost gauge and see where it's getting to when it cuts out. It should get into the red, 1/3 to 1/2 way, before cutting the fuel.

Neil

[mutungi]

No...not FPT but LPT with no dash gauge....also when set to cruise...hiccups like mad every time it needs to boost to maintain set speed, then have to get it off cruise to drive normal.

[wulbert]

muntungi. I have an identical problem with my '93 LPT when I run it on LPG from cold.( It's duel fuel) I've noticed that this seems to be acompanied by a hissing sound during the misfire.I've wondered if this is an overboost problem but know nothing about how this works,Is it as sudden as this when the protection cuts in? It's a sudden loss of power which isn't restored until you back of the throttle.

[wulbert]

muntungi. I have an identical problem with my '93 LPT when I run it on LPG from cold.( It's duel fuel) I've noticed that this seems to be acompanied by a hissing sound during the misfire.I've wondered if this is an overboost problem but know nothing about how this works,Is it as sudden as this when the protection cuts in? It's a sudden loss of power which isn't restored until you back of the throttle.

[9000CS23T]

Have you checked to see if your waste gate is working? If not this can cause the overboost problem. I had this problem on my FPT, the wastegate was seized. Took the turbo off and cleaned it and it seems to have been ok since.

HTH

Neil

[mutungi]

Neil...how do I check the wastegate on the turbo? Where is it? BTW this is LPT....same turbo as FPT?

[9000CS23T]

The turbo is different, but should be the same setup. Do this when the engine is cold. Reach down behind the exhaust turbine side of the turbo unit, you should find a rod coming out of a silver cylinder, and attached to a lever at the other end(left looking from front of car), this is the wastegate rod. Although it could be quite stiff, you should be able to move this rod. This action opens and closes the wastegate in the turbo. the only way i could move mine initially was with a large lever bar. If you can't budge it at all, it could well be seized up with soot.

If it is seized try to get some WD40, or similar, into the lever sleeve and work the lever, you can disconnect the rod by removing the "R" clip and pulling it off.

Bit long winded but hope you understand it.

Neil

[Paul D]

If you can determine that the wastegate is OK, then maybe the previous owner had the boost wound up on the turbo (i.e. a bit too much) by adjusting the linkage between the actuator and the wastegate. This is easily done (if it isn't rusted) and would still make the car seem standard by all appearances.

The ECU on the 2L LPT limits boost to around 0.6 bar, so it is easy to reach overboost if any linkage adjustment occurs.

Alternatively the actuator may have failed, but they are extremely robust, and this is unlikely.

I have found that significant soot build up in the wastegate is hard to clear with Plus Gas/WD40, and a strip down and clean of the wastegate part of the Turbo may be required. Cost me £50 by a local garage on one occassion, although sevveral Turbo specialists tried to sell me a new Turbo, including the main dealer in Cardiff!