86 turbo se, boost wont go past .5 or .6

[lordv8dr]

58,000 miles, 86 turbo SE HC: coolant light came on, low coolant in the header tank (I hadn't checked it in a while), don't see any leaks now that it's full. Turbo won't kick in hard anymore, gauge won't go past .5 or.6 even after it is at warm temperature. What should I check? Is my turbo going bad or is it bad? thanks.

[lotusguy]

Hi,
Sorry to hear of your problems. Keep an eye on the coolant level because a drop, combined with low boost could be the result of a leaky head gasket. But, before you go all crazy, most boost problems are the result of a vacuum leak or disconnection. Carefully check all the vacuum hoses for splits and make sure they are properly attached. Also, disconnect your air intake hose to the turbo and check inside the hose and turbo outlet for the presence of oil. If you find some, your turbo bearing is going away. Hope this helps...Jim '85TE

[RyanSheldon]

I had the same problem, had the turbo rebuilt, but still did not fix the problem (the old turbo was completely shot). I replaced the large hoses that went from the turbo to the chargecooler. It seems there was a small leak that was keeping the pressure building, even though the hoses looked great. A reset of the ECM never hurts as it can electronically limit boost pressure. Hope this helps.
Ryan

[lotusguy]

RyanSheldon said: I had the same problem, had the turbo rebuilt, but still did not fix the problem (the old turbo was completely shot). I replaced the large hoses that went from the turbo to the chargecooler. It seems there was a small leak that was keeping the pressure building, even though the hoses looked great. A reset of the ECM never hurts as it can electronically limit boost pressure. Hope this helps.
Ryan

Ryan,
Great advise, but I'm not sure it's applicable here. Our friend states that he has an <'86 SE HC >?? No such animal, unless it's an '86 w/ a transplanted SE motor. I believe he may be confused and merely has an HC w/ Bosche K-Jetronic - no chargecooler and no ECM.

Aside from that, I agree with you that it's most likely a vacuum leak or bad hose connection... Jim '85TE



>> Edited by lotusguy on Wednesday 4th December 07:58

[lordv8dr]

jim, thanks, yeah, i was confused, i have an 86 turbo esprit hci, i'll check the hoses and stuff(anything else you can think of that I should check would be greatly appreciated). If everything looks good to me would you probably suggest that I still take it in to my mechanic as there is most likely something wrong ?

Thanks
Phil, 86 turbo esprit hci

[cnh1990]

Check the plugs if the engine is not running smooth during boost, That will keep you from getting full boost. my plugs do not last too long. When was the last time you changed them?
Calvin

[lotusguy]

lordv8dr said: jim, thanks, yeah, i was confused, i have an 86 turbo esprit hci, i'll check the hoses and stuff(anything else you can think of that I should check would be greatly appreciated). If everything looks good to me would you probably suggest that I still take it in to my mechanic as there is most likely something wrong ? Thanks Phil, 86 turbo esprit hci

Hey Phil,

It's ok to be a little confused with all the various designations governing these cars.

Again, if you find all vacuum connections are good and not leaking, given your mileage, I would suspect the turbo may be going away. A simple check is to see if oil is seeping through the bearing seal into the outlet side and inside the intake hose. Really should be dry, but with 58k, I might expect to see some oil film, but no actual liquid. If you detect liquid oil, it's turbo rebuild time.

Another thing which is suspect is whether or not your throttles are opening fully. If not, causes can range from a stretched or misadjusted throttle cable (esp. @ 58k mi.), a misaligned or malfunctioning throttle position switch.

If all these check out, look for possible, leaky cold start injector, leaky auxillary air valve, reduced function in either the primary or secondary fuel pumps (or both), a misadjusted fuel regulator (either insufficient Cold or Hot Control Pressure) or clogged injectors.

I see Calvin suspects your spark plugs. This is not likely the cause, but a good item to check nonetheless, along with the high tension leads. You may also find that switching to a cooler plug may help as well. The spec plug is the NGK-BPR6EY, try the NGK-BPR7EY. My car prefers this cooler plug to the stock one and idles and boosts much smoother with them.

You can check for leaks, the turbo and throttle opening yourself. If these check out, I doubt you have the test equipment necessary to check the other components and will have to leave these to your mechanic. Make sure he thoroughly understands Bosche K-Jetronic. If he doesn't, find someone else who does as it can be a little tricky to get right. Hope this helps... Jim '85TE (With waaaay too much Bosche K-Jetronic experience)

[cnh1990]

When it happened to me the plugs were not fouled they were burnt out (fried/eroded porcelin and electrodes). Car would not boost very high and there was a little stutter on wide open. When it should be boosting up to 1 bar without a miss as it normally does. On a 86-87 HC engine what is the normal boost anyways. I thought it was about 8lbs. which would be around .6 bar. So it may be normal. What you think Jim?
Calvin

[lotusguy]

cnh1990 said: When it happened to me the plugs were not fouled they were burnt out (fried/eroded porcelin and electrodes). Car would not boost very high and there was a little stutter on wide open. When it should be boosting up to 1 bar without a miss as it normally does. On a 86-87 HC engine what is the normal boost anyways. I thought it was about 8lbs. which would be around .6 bar. So it may be normal. What you think Jim?
Calvin

Calvin,

Sounds like you may be happier with a cooler plug as well. Each engine is different as well as your driving habits and available fuel grades and variances in purity. I was amazed at the difference cooler plugs made in mine and it only costs you about $8 to see if they work better. And there is never any danger in switching to a colder plug, which of course is not necessarily the case in going to a hotter plug. FYI, the basic difference in a colder or hotter plug is the shape of the electrode insulator. A cooler plug's insulator entends a little further down the electrode allowing the plug to absorb less heat than a warmer one. The length of the plug stays the same, just the shape of the insulator is different.

As far as the maximum boost pressure on an HC 910 engine, Spec is 0.65BAR or 9.5PSI stock w/ a compression ratio of 8.0:1. As you know, I am running 0.69BAR or 10PSI @ 8.5:1 compression ratio (no intercooling) for near 5,000 mi. w/ no problems, so a stock HC motor should be good for 0.75BAR or 11PSI with no problems, w/ a simple wastegate adjustment...Jim '85TE



>> Edited by lotusguy on Wednesday 4th December 20:36

[cnh1990]

The SE uses a specific plug with a twin circular electrode (they are spendy). The erosion on the plug is just the nature of the turbo boost heat. The plugs I had trouble with were the standard plugs they use in non SE/S4/S4s turbo cars with single electrode. The PO had ordered a tune up when I went to pick up the car and they must have put in the non SE type plugs in by mistake. They did not last very long. I consulted with Keen and Dan, they both concur that the SE's should use the NGK plugs of the ERK designation. Keen and Dan have told me that regular plugs burn out after 5K miles or less. About the turbo, on stock SE setting they limit the boost to .8 bar even with the intercooler with a fast spike of about a second to 1 bar before settling down to .8 bar. Many times stock SE's do not even spike to 1 bar as it depends on what gear and speed you are at when you open it up. So just wondering how much boost in G cars with stock waste gate and BOV settings before they bleed off the boost.
Calvin

[lotusguy]

Calvin,

I wasn't suggesting the previously listed plug numbers for your car, but I am also sure that NGK makes a temp range in the ERK line as well.

As far as the boost in the HC motor, the 910 HC motor does not have a BOV or Plenum Purge Valve as it is called. This exists only on the 910 STD engined carb'd cars and opens somewhere around 12PSI which is where the pressure spikes on rapid deceleration. Other than that, without an ECM, the system is really analog relying soley on the wastegate spring pressure to prevent overboost by dumping the exhaust gas pressure to the muffler and tailpipe. This spring pressure rate is adjustable either by rotating the wastegate diaphram adjusting screw, if so equipped (like mine), or by adding/subtracting spring shims (like Glen's '88). A hard line runs from the turbo (pressure side) down to the wastegate, where it acts on the wastegate diaphram and plunger. If the wastegate sticks on an 910 HC motor, the engine will overboost, on my car, once 12 PSI is reached, the Plenum Purge Valve will open dumping the boost to atmosphere. ..Jim '85TE

[cnh1990]

Jim,
I know you weren't suggesting I use the standard plugs for the SE. I made a mistake in the plug designation. The correct plug number for my car is The NGK BPR6EKN with the twin electrode. I'll stick to recommended plug for now as that is what the rest of the SE's have good luck with. I only have 3K miles on them. The only reason I the previous ones eroded was it was the wrong plug and the heat cooked it. When I got home from work I did look up the stock boost figures for the 88 which is just a re-skined 86-87 G car. Max boost for the stock HCI engine is .65 bar/9.5 lbs. of boost. The SE stock engine max boost is .84 bar/12 lbs. So the it's not too off the mark. He probably does have a leak some where if he can't reach .6 bar.
Calvin