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Engine Miss, Loss of Power???

My 86 turbo which has run flawlessly for me for a year, started occasionally missing with loss of power.

The car has 125,000 miles and the engine appears to be stock, unknown history of engine work (I've owned it for 1 year) but the engine runs good, pulls hard (that's what she said) and never misbehaves until Sunday.

I took a short 1/2 mile trip from home; everything ok. Then 1/2 hour later, repeated the 1/2 mile trip back home, idled for a minute, then went to leave. As I got out of first gear and slightly let off the accelerator the engine sort of died. As I pressed the accelerator more, the engine coughed and popped still no power. I quickly turned the ignition off then on and power came back and engine ran fine.

2nd time this happened later the same day, again it seems as when I deaccelerated, it lost power, turn ignition off, then on and it ran fine.

Thursday I took the car to work 80 mile round trip and the car ran fine.

Yesterday it happened again seemingly when I deaccelerated and this time the turn off/on trick didn't work and the car totally died and I rolled it off the road. Started it up and it ran fine. Did this 2 more times, pulled over, started it back up, and ran fine.

I notice sometimes when I start it up, it doesn't idle at 1K like it has since I bought it, but idles roughly at about 700 RPM, then just like someone flipped a switch, the engine idle speed will jump to 1K and it idles smooth.

What does this sound like? It seems to happen when I let off the throttle when running. Wastegate sticking? Doesn't seem like fuel pressure since it happens or seems to happen when letting off the throttle.

Thanks in advance for your help.

Last edited by spoke; 04-04-2010 at 06:42 AM..
Old 04-04-2010, 06:40 AM
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This turning the key on and off, which fixes things, and the occasional rough idle that myteriously smooths out at the snap of your fingers, makes me think CDI ignition module. Or, could be as simple as a loose coil wire, or other loose stuff (man, if that isn't vague....).

Also look at your fuel pump connections up at the fuse box. Unscrew and pull the wires from the fuse mounting points, clean them well, reinstall and torque down. Clean the fuse and it's contacts, pull the red pump relay and clean the pins and expand them slightly for a nice tight fit when plugged back into the socket.

The next time it does this you need to do some diagnostics to determine spark or fuel related. Are the pumps runnning (key on, pull the connector plug back behind the metering plate in the fuel head). They should run at that point. If not, that will tell part of the story.

There's a whole littany of stuff to look at.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 04-04-2010, 05:15 PM
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Why, oh why do our cars do this to us, with all the love we give them? They are worse than women sometimes.
Old 04-04-2010, 06:51 PM
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I don't think our cars mean to hassle us... they just truely love to be driven fast :-).
Old 04-04-2010, 08:09 PM
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A couple of times today, the car wouldn't start at all. It turned over like there was not spark or fuel. When I would turn the key on, I didn't hear the fuel pump run for the few seconds that it normally does when I turn the key on.

I reseated the yellow relay in the engine compartment and the car started running real good and the fuel pump runs now for a second when the ignition is turned on.
Old 04-10-2010, 06:03 PM
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Damn yellow relays....Glad you're back on the road.
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Old 04-10-2010, 06:16 PM
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Mark, It doesn't sound like it's running, but for a second or two. I'd jump the yellow relay with a wire between # 30 and 87 IIRC. If it runs good, then clean all the contacts for the relay and spread the male portion of the relay legs to have them seat better.

Other than that, your looking at the CDI, delayed cut off relay, etc.
Old 04-10-2010, 06:57 PM
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Quote:
Originally Posted by A930Rocket View Post
Mark, It doesn't sound like it's running, but for a second or two. I'd jump the yellow relay with a wire between # 30 and 87 IIRC. If it runs good, then clean all the contacts for the relay and spread the male portion of the relay legs to have them seat better.

Other than that, your looking at the CDI, delayed cut off relay, etc.
Yo Spoke! She running, or not?
"The car started running real good and the fuel pump runs now for a second when the ignition is turned on".

My yellow relay functions such that when I first turn the key on, the pumps run for just a nano-second...just to remind me that they're there I guess and maybe to prime things just a bit before twisting the starter. That's with a new relay...my old one didn't do that short pre-run. Is this what you're referring to, or is she dying after a second of running?

Brian's advice is right on, but IIRC for my car anyway I needed to short between terminals 87 and 87A (I even made a short piece of highly customized wire as a jumper, which resides in the glove box just in case). Do that and the pumps will start running as soon as you turn on the key, as opposed to waiting for the metering plate to be deflected with the engine cranking.

Please say she's running so we can all sleep at night.
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Old 04-10-2010, 07:16 PM
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Quote:
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Yo Spoke! She running, or not?
"The car started running real good and the fuel pump runs now for a second when the ignition is turned on".
The car is running great again. It would run great then just die or try to die. Now with the yellow relay reseated, it runs great. Problem solve I hope...
Old 04-11-2010, 05:11 PM
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Damn yellow relays.... :-)
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Old 04-11-2010, 05:34 PM
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What are the part numbers for these relays, yellow etc so I can get one or two for spares?
Old 04-11-2010, 07:46 PM
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I don't recall the part numbers, the black and red relays are about $20-25 each.

The yellow relay is about $125-150, I'd probably get just one of those...
Old 04-12-2010, 02:05 AM
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I found out that I don't have a yellow relay since I have a 79 but I still need to get a red relay.
Old 04-12-2010, 05:56 AM
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Red or black, there not supposed to be interchangeable. I think you want black. Red ones have a diode I understand.
Old 04-12-2010, 09:57 AM
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OK, still having issues with the fuel pumps. When I turn the key to on, the pumps run for a second then stop.

For some reason, when I start the car, the pumps either run or not. If they run, the car runs good. If they don't run, then the car fires at first (because of the 1 second pump run when key turned to on), then dies.

Sometimes on subsequent re-start tries, I won't hear the 1 second pump run when key turned to on and the engine won't even stumble when trying to start it.

I thought it was the contacts on the yellow relay but not sure now.

I'm trying to diagnose the problem. I have schematics for the car but what I don't have is the location of each of the relays, switches, and such. Does anyone have a layout description of each of the components in the 930?

What I'm looking for in particular are:
1) Air Flow Sensor Charging Pressure Relay (I think this is the yellow relay)
2) Air Flow Sensor Contact
3) Speed Relay
4) Charging Pressure Control Switch

The names of these components come right from my schematics. I don't know where to find these pieces. If I did, it would help in the diagnosis of my problem.

Thanks in advance,
Spoke

Last edited by spoke; 05-22-2010 at 07:20 PM..
Old 05-22-2010, 07:17 PM
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I would narrow it down by first removing the yellow relay and jumping across the two points as mentioned above. Take that sucker out of the equation, in other words. Then, with the key on but the engine not running, if the car is stock wired you will not hear the pumps run until or if you depress the air metering plate slightly to actuate the micro switch, or reach behind the fuel head and pull the blue electrical plug off. Either of these actions will cause the pumps to run.

Do check the condition of the wire (white?) that's connected to the overboost pressure switch. That wire forms a ground connection, without which the yellow relay won't energize and the pumps won't run. If the switch itself is suspected to be toast, then simply pull the wire and ground it to the engine somewhere. Step by step process of ellimination.
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Old 05-23-2010, 05:56 AM
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Thanks for the info.

Good Idea about jumping the yellow relay. I'll keep that in my back pocket if this issue leaves me stranded. I threw a little jumper wire in the trunk in case it leaves me on the side of the road before I figure this one out.

Can you give me an idea of where to find the overboost pressure switch?

So I just noticed this little box named Permatune. Sorry for the fuzzy pic. This doesn't look stock or is it? It was made in the good ole' USA.

Old 05-23-2010, 08:04 AM
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The overboost pressure switch is mounted at the top end (toward the front of the car) of the boost recirculation piston valve assembly. If you peek around the left side of the intercooler and back into the deep dark recesses of the engine, you should be able to see it. It's just a simple pressure switch screwed into the manifold.

The Permatune is a replacement for your otherwise missing stock CDI ignition module. Permatune and MSD ignition systems are popular aftermarket stuff....I run with the MSD myself.
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Last edited by mark houghton; 05-23-2010 at 01:52 PM..
Old 05-23-2010, 01:50 PM
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I haven't found the overboost switch yet but I do have the yellow relay wired for next installment of "The ***** won't start" episode.

The wires are on pin 85 to check the Air Flow Sensor, and pin 87a to check for continuity through the Speed Relay and Charging Pressure Control Switch.

I've got my voltmeter, schematic, jumper wires, and flashlight in the car in case this happens on the road.

Old 05-24-2010, 02:11 AM
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You've got an earlier version of the infamous yellow relay, with the brown wire coming out the side, so the terminals you jump across may be different that what we've directed. No problem, as you've apparently done your own homework on the work-around as to which to short across. Have you confirmed that your pumps run with the jumper in place and the relay completely removed?
As to the overboost pressure switch, here's a diagram that may help point you to it's location (open the link and click on the diagram)
Pelican Parts - Product Information: 930-606-101-00-M100
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 05-24-2010, 12:28 PM
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