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No-start brain teaser[240-260/88] posted by Don Foster on
Monday, 15 June 1998, at 7:42 a.m.
Here's a description of a problem and an example of how easy it is to be mislead by the data.
During the last several weeks, I've been helping a friend solve a problem on an '87 non-turbo 740. He owns a one-man, Volvo-only shop. The car, not registered, came from a body shop that had bought it to fix up and resell.
We solved the problem (finally), and I'm passing on the symptoms, information, and data -- and final results -- to everyone. There's a lesson or two. After several days, I'll post our findings and success.
Here's what the customer (body shop) said:
"It ran and drove fine before we replaced the fender."
"It wouldn't start after we worked on it."
"It starts and runs if you squirt gas into a vacuum line."
"We checked everything we can think of under the hood."
"It cranks GREAT!"
Here's our work, observations, tests, etc.:
(I might have one or two of these steps out of order.)
- Gas tank almost full, told it was fresh gas (it was).
- Cranks like crazy.
- Has excellent spark.
- Ignition timing at about 10 BTDC (+/-) while cranking.
- New plugs, always come out clean, fresh, dry.
- New fuel pump relay.
- Replaced injection module.
- Checked voltages at injection module harness connector -- all OK.
- Checked grounds at same connector -- all OK.
- Checked and retightened grounds at injection rack.
- Checked for 12 volts at pin 1 (signal from ignition module) -- 11 volts -- close enough.
- Swapped ignition module anyway.
- Plugged both modules and relays in known-good and running '87 -- all parts OK.
- Checked for voltage at injectors -- ZERO VOLTS.
- Found cracked (broken) connector at plug (up inside the insulator) to suppression relay!!
- Replaced connector -- cranked like crazy.
- Fuel pressure measured at about 2.7 kp/cm (at injection rack using Volvo gauge).
- Plugs still look clean, fresh, new. And dry. No smell of fuel.
- Detected pulsed ground at injector plug.
- With stethoscope, able to hear injector clicking during cranking. (Compared favorably to test car, while cranking, with coil wire pulled.)
- Pulled injectors and rack -- injectors spray fine while cranking.
- No gasoline smell at exhaust pipe.
- Reinstalled injectors, cranks like crazy, but won't fire.
- No fingerprints around timing belt cover.... nobody's been in there recently.
-------------------------------------------
We made one more (very basic) test, made one simple addition, and had the car running in 5 minutes.
As I said, this is an example of how to be misled and how to miss the simplest data.
So here's the pop quiz:
What did we measure, what did we add, and what had happened?
Don Foster
Re: No-start brain teaser[240-260/88] posted by Mike on
Monday, 15 June 1998, at 10:34 a.m.
Assuming the timing belt was still attached (evidenced
by the fact that you say you can spray fuel in a vacuum
line and the car will start and RUN - perplexing)...
Did you do a voltage drop check to look for a bad ground?
Still, this doesn't explain why the injectors are
firing while pulled out on the rail but not when
installed.
Re: No-start brain teaser[240-260/88] posted by Don Foster on
Monday, 15 June 1998, at 10:56 a.m.
We checked the grounds to the engine, to the chassis, to the components, and to the battery. All were fine.
I never said the injectors weren't firing when installed (although we sure thought about that -- we even pulled a complete injector rack off a known-good parts car thinking the injectors had been damaged when the body shop welded).
I did say that the injectors "clicked" just like good ones when using the stethoscope, and that was with them installed.
We really chased our tails around on this!
But then, a good education always costs something.
Don Foster
Re: No-start brain teaser[240-260/88] posted by john on
Monday, 15 June 1998, at 1:46 p.m.
I don't see where you checked the compression and "no finger prints on the cam cover" indicates no one looked at the belt. When an engine "cranks like
crazy" I'd guess they mean fast, which means no compression. Also no gas smell at the exhaust pipe means no air flow thru the engine=cam belt off or out of
time.
just a guess
Re: No-start brain teaser[240-260/88] posted by Don Foster on
Monday, 15 June 1998, at 2:03 p.m.
John ---
Good guess.... but we had spark (e.g., cam & distrubutor turning) and the previous mechanic reported that it ran when fuel was introduced into the intake. I accept that it did.
My comment on fingerprints: What I was trying to do was prevent getting sidetracked on a discussion that someone had gotten inside and fouled up cam timing. They hadn't.
There was flow through the engine. The plugs were dry as a bone all 100 times we checked them (well, maybe only 3-4 times, but it seemed like 100).
Please continue with your thinking about compression.
Don Foster
Re: No-start brain teaser[240-260/88] posted by George Swift on
Monday, 15 June 1998, at 3:31 p.m.
You measured the engine compartment, You added 4 cylinders, (V8), and you got your first speeding ticket in that car.
No ? You probably measured voltage drop and added a ground wire to the block. Do I win yet?
curious george
--George Swift / Volvo Car Care
Re: No-start brain teaser[240-260/88] posted by Dick Grinnell on
Monday, 15 June 1998, at 7:13 p.m.
The timing belt has slipped, not broken, and the cam-ignition is out of time with the crank: no compression. It may have run when gas was injected in the vacuum line, but now the belt has slipped more and it probably won't.
Dick Grinnell
This is my last guess.[240-260/88] posted by George Swift on
Monday, 15 June 1998, at 9:42 p.m.
You added oil to the cylinders because the compression was low, but I would have heard that. Shit, you said it started with raw fuel. Nevermind. Tell us please please please please please !!!!!!!
--George Swift / Volvo Car Care
Re: This is my last guess.[240-260/88] posted by Don Foster on
Tuesday, 16 June 1998, at 10:21 a.m.
George ---
Why is the last guess always the right one? And why am I not surprised you got it?
We measured the compression -- it was around 75 psi. "Cranked like crazy." I said that enough times!!!
We added oil to all four cylinders -- compression jumped to 160 -- it started immediately. Smoked like hell for a coupla minutes, but ran and sounded fine. And it started immediately this morning, too.
After all that -- it's amazing how these simple problems seem so obvious, and EMBARRASSING in hindsight. And how much time we wasted by misleading ourselves.
Like I said, education costs.
Several others should be credited (Dick and John) for mentioning compression also. But they didn't get to the oil.
We figured the previous mechanic washed the oil off the cylinders with the gasoline, kept trying, and made it worse. When we fixed the broken wire, we proceeded to flood (and wash) the rings even more. All the time we ignored the freewheeling cranking, and kept studying the schematics, making measurements, and trying various fuel injection and electronics solutions.
Apparently, there was so much clearance between the rings and the bore that the gasoline going into the cylinder ran down the walls without wetting the plugs.
Oh, yeah -- we changed the oil and filter, too. There musta been several quarts of gas in with the oil.
Well, this was interesting. Let's try some more brainteasers! Who's next?
--Don Foster