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Discussion Starter · #1 ·
Got the S4s out after the winter sleep. Runs good but boost is only showing 0.5 bar, and it stops at a very consistent point on the gauge. Was close to 1 bar before. Sounds like the wastegate is opening at its mechanical limit, and that the electronic system to increase that is not working. I read the service manual section on how that system works, there are quite a number of things that have to be present (throttle position, rpm, temperature, etc).

I will go through all those things when I get a chance, most of them can be monitored on Esprit Scan, but what are the common failure points for this? There must be at least 20 different places this system can fail when you include all the vacuum hoses. What's should I look for first?
 

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Cal H
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Quick question. You said "out after winter sleep"
Does than mean battery was disconnected?
If so that will trigger ECU safe mode in learn cycle and will limit boost for what appears .5-.65 bar for about 30 miles (per Marcus) until the chip beds in. It will happen every time the ECU is rest. Use standard bed in/warm up procedure and see if that is the problem Another person claimed 100-150 miles or 1/2 tank of gas in learn mode before full boost but that is also another person opinion on how long learn mode lasts.
 

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I had the same issue as you know, found a cracked hose that went to the boost controller that sits on the trunk wall on the engine side. Traced it all using the diagram on the under side of the hatch lid. I also had a stuck thermostat but even after replacing it I was still having boost issues. Replaced the tube and back to normal. That was the first time. The second time I would get full boost and it would then back off after making boost. Turned out to be a bad hose at the fuel pressure regulator.
 

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Discussion Starter · #4 ·
Quick question. You said "out after winter sleep"
Does than mean battery was disconnected?
If so that will trigger ECU safe mode in learn cycle and will limit boost for what appears .5-.65 bar for about 30 miles (per Marcus) until the chip beds in. It will happen every time the ECU is rest. Use standard bed in/warm up procedure and see if that is the problem Another person claimed 100-150 miles or 1/2 tank of gas in learn mode before full boost but that is also another person opinion on how long learn mode lasts.
Nothing disconnected, but keep those ideas coming. Just sleeping with the battery tender plugged in. I did drive it 40 to 50 miles before noticing the boost was not full. Surprising how well it performs even with 0.5 bar on the gauge (which I assume is actually the 0.65 bar mechanical limit according to the service manual).
 

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Discussion Starter · #5 ·
I had the same issue as you know, found a cracked hose that went to the boost controller that sits on the trunk wall on the engine side. Traced it all using the diagram on the under side of the hatch lid. I also had a stuck thermostat but even after replacing it I was still having boost issues. Replaced the tube and back to normal. That was the first time. The second time I would get full boost and it would then back off after making boost. Turned out to be a bad hose at the fuel pressure regulator.
Hoses are definitely a possibility. Besides age, could be one of the pesky critters ate one.

The book shows where those relays are mounted on the SE models, behind the carpeted cover. On my S4s that compartment contains the vacuum pump. Where did the relays and solenoids move to?
 

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Hoses are definitely a possibility. Besides age, could be one of the pesky critters ate one.

The book shows where those relays are mounted on the SE models, behind the carpeted cover. On my S4s that compartment contains the vacuum pump. Where did the relays and solenoids move to?
Directly on the other side. Peek your head over and they are next to the coolant reservoir.
 

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Wingless Wonder
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Hoses are definitely a possibility. Besides age, could be one of the pesky critters ate one.
Yup, CarSalesman DOES have critters where he lives! (Don't ask me how I know this!)

:rolleyes:
 

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Quick question. You said "out after winter sleep"
Does than mean battery was disconnected?
If so that will trigger ECU safe mode in learn cycle and will limit boost for what appears .5-.65 bar for about 30 miles (per Marcus) until the chip beds in. It will happen every time the ECU is rest. Use standard bed in/warm up procedure and see if that is the problem Another person claimed 100-150 miles or 1/2 tank of gas in learn mode before full boost but that is also another person opinion on how long learn mode lasts.
Hello.
Does this also apply for an 89 non SE?
Thanks.
 

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Hello.
Does this also apply for an 89 non SE?
Thanks.
Applies to all GM computer 4cyl.

The recommended way to teach the computer after a battery disconnect is to start with a cold car. Turn ignition on, leave motor off, give throttle pedal a full to the floor travel. Then start car without touching throttle, let it idle till temp rises to 80. While it is warming up keep a load on the motor by running headlight/AC. Once it is warm drive the car moderately for 5-10 miles, then begin more spirited runs.

I usually get a few brief overboosts till the computer learns, but everything works well after about 20 minutes.

Randy
 

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Don,

What's the condition of your charge cooler impeller?? That could possibly be causing you not to achieve full boost. My impeller needed to be replaced this past year. I noticed an immediate difference when it was replaced.

Dom
 

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Base boost is determined by the tension of the wastegate capsule, it should be around 0.6 or so, but can be adjusted. To get more boost the computer has to be happy, meaning adequate temp, proper gear, adequate throttle.
Then the hoses to the capsule and the solenoid need to be sound. A non functioning solenoid will prevent override of the base boost setting. I had that problem when I bought my car. New solenoid solved it.

Randy
 

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Cal H
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Yep could be the impeller or could be other things like faulty engine temp sensor (the one for ECU not temp gauge) as well as leaky/disconnected hoses and solenoids. He's got freescan or Esrit mon so he is a lot better than off than most.
 

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Cal H
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Base boost is determined by the tension of the wastegate capsule, it should be around 0.6 or so, but can be adjusted.
Randy
Best not to mention capsule adjustment unless you absolutely have too. In the past when we talked about this it tempted people to started fiddling with the adjuster and spun the rod instead of the nut and tore the capsule membrane rendering it useless. Boost will always be a hot topic and people always want more of it regardless of if it is good or bad.
 

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Applies to all GM computer 4cyl.

The recommended way to teach the computer after a battery disconnect is to start with a cold car. Turn ignition on, leave motor off, give throttle pedal a full to the floor travel. Then start car without touching throttle, let it idle till temp rises to 80. While it is warming up keep a load on the motor by running headlight/AC. Once it is warm drive the car moderately for 5-10 miles, then begin more spirited runs.

I usually get a few brief overboosts till the computer learns, but everything works well after about 20 minutes.

Randy
:up:
 

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Yep could be the impeller or could be other things like faulty engine temp sensor (the one for ECU not temp gauge) as well as leaky/disconnected hoses and solenoids. He's got freescan or Esrit mon so he is a lot better than off than most.
Checking to see if the impeller is functioning is very easy. Simply get the car hot, do a couple of spirited runs, immediately stop the car and raise the lid and feel the chargecooler. If it hot, your pump is not working, if it is noticeably cooler that the rest of the motor, you have a functioning pump.
 

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Discussion Starter · #16 ·
Thanks for all the tips. My impeller is new about 1,500 miles ago. Ralph (RS Motorsports) replaced it as part of a very thorough C-service, new tensioners, rebuild water pump, all that stuff. I haven't had time to investigate yet, but my money is on the "critters" and the hoses.
 

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I took my car out for the second time.
It was very different upon acceleration as opposed to the first time.
The battery was drained completely prior to the second drive and of course I recharged it.
This explains it.
 

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Discussion Starter · #18 ·
Closing the loop on this one. I did a visual inspection, all the hoses and connections looked right. Checked everything with freescan, everything there looks good. Reading the service manual, there is a separate learning process for the pulse width boost modulation. I always knew about the idle learn process, but this is a separate process that only happens when in the overboost mode (over 0.65 bar). Basically you have to run it hard several times so the computer can learn how much modulation it takes, so it knows where to start the next time.

Works fine now. Just shy of 1 bar, right where it should be on S4s.
 

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That is great news!
 
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