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 Need diagnose help: '94 Caprice w/LT1 ignition prob

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jvette65



Posts: 111
Join date: 2010-02-16

PostSubject: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 6:14 am

Hi Guys, would like some suggestions on this one. Son's 94 Caprice w/LT1 developed this problem late last week, almost left him stranded, don't know if the wet weather had something to do with it.
Fuel pump running, engine turns over, has fuel (will check pressure), but does not want to ignite. Usually it starts only after a couple of rev's. But now to get it to start I held the accelerator all the way down and it starts up running rough, then idle smooths out after it gets warmed up (with some help on the accelerator). Once warm to normal operating temp it runs ok on it's own, but the idles seems high, and when you step on the gas, there's a stumble then it winds up. I get good acceleration out of it, but the idle seems off. Shut the engine off, and I have to go through the same procedure to get it running again. It has newer plugs, wires. Car's been running excellent up till last Friday.
Any suggestions? I was going to check operation range of TPS then IAC first. The pcm hasn't set any codes. Thanks in advance. -Joe
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sdstick



Posts: 4077
Join date: 2009-03-20
Location: Revere, MA

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 6:23 am

My temp sensor in the water pump went bad & thats exactly what happened to me.

Also note: If the fuel pump isnt suppliying proper pressure (1st prime insufficient) you could get the hard start. That should only be a hard start tho. Check that by priming the fuel pump 2X before starting.

Yours sounds like PCM is not getting temp reading from temp sensor.

_________________
Steve


96BBB 28K 3.42 Bolt-ons
95BBB 100K 3.73 383 New DD...already broke the 4L60E
95 Black WB4 Hole...ee...grail
95BBB 189K 3.08 Old DD Stolen...by Matt. Cool
Whine..eee...Silver LS6
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MASShole9C1



Posts: 3764
Join date: 2009-12-15
Age: 27
Location: We must not compromise territorial range

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 6:51 am

Is it the original opti spark? How many miles? I had some of the same symptoms and was told to chase all kinds of stuff, when my guess was the opti. I canged the opti, plugs, and wires, and its like I have a new daily driver!
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jvette65



Posts: 111
Join date: 2010-02-16

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 8:25 am

Hi , I tried the 2x prime before cranking and it still wouldn't start normally. The temp semsor of the water pump is an easy check, I'll do that first.
The opti is original to the engine and it's at 80K. The wires and plugs were replaced year before last. This prob suddenly started happening after that last big slush storm. Do you
think the opti could have got soaked that bad? I checked the vacuum draw on the opti vent harness at the fresh air fitting and I was getting a vacuum.
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sdstick



Posts: 4077
Join date: 2009-03-20
Location: Revere, MA

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 8:41 am

80K is in the area of opti life but I cant diagnose that, Brian just went thru that joy.
When I lost mine, it started hard but ran fine. Each time it was moist out the hard start happened, getting worse until I gave in & changed it.

When my ECT sensor went, I had to floor the pedal to start, then it would rev & run ok, once it warmed up it would stumble & misfire. It was frustrating. When I re-read yours, it sounds opposite, runs ok when warm. Not the same symptom as mine.

_________________
Steve


96BBB 28K 3.42 Bolt-ons
95BBB 100K 3.73 383 New DD...already broke the 4L60E
95 Black WB4 Hole...ee...grail
95BBB 189K 3.08 Old DD Stolen...by Matt. Cool
Whine..eee...Silver LS6
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96slowss



Posts: 845
Join date: 2010-06-09
Age: 26
Location: Halifax,MA

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 8:44 am

its ur coolent temp. sensor.. when it goes bad the motor goes into a 0 degree mode. it acts as if its 0 degrees out and dumps extra fuel into the motor so when u floor it its give u alot of air also. allowing it to start and once the motor warms up it will run better.. its a simple part just change it when the car is cold. so theres not alot of pressure behind it..
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MASShole9C1



Posts: 3764
Join date: 2009-12-15
Age: 27
Location: We must not compromise territorial range

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 8:45 am

Well, to explain, I can tell you what happened to me. When driving in hard rain and splashing through puddles, the car would act like it was misfiring, and with the peddle to the floor, nothing would happen. The engine would choke on the side of the road for a few seconds and shut down. When I'd try to restart it, it would just crank and crank. Sometimes running as if it were hydraulic with spurratic turns of the engine and then quite. It would start after about 30 minutes or, if I sprayed brake clean or WD40 around the opti area. A month ago, it snowed overnight and the engine wouldnt run at all. It would just crank. I left it with the hood open in direct sunlight for 2 hours and it started right up. The last big snow storm was the last straw. It wouldnt start for days. Took everything apart, long story short, the new opti fixed the problem. Ive driven through every puddle Ive found the last week with no problems, and sitting in the snow overnight, it started right up today with no problem. I had vacuum, coolant signal, the fuel pump works, etc. Make sure the water pump isnt leaking on the opti. I got away with having a new pump, so that didnt trigger the problem. My guess is that there is moisture on the crank sensor and it will freeze over night. These cars(as most today) wont start without a CKP signal at the turn of the key. But it varies from situation to situation. I hope you figure it out!
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jvette65



Posts: 111
Join date: 2010-02-16

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 9:13 am

I guess what's throwing me off is that the car is still hard to start after warm-up. When warm it does have good acceleration, fast idle, but running rich and has the stumble. I still have to floor the gas to get it to re-start after I shut it off. But it's also probably due for an opti rebuild. I'll get the parts this week and try it out. I have a known good ect , I'll try that first and then move to the opti. Thanks for the help, I'll let you know how it works out. -Joe
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boojum



Posts: 2031
Join date: 2009-01-21
Age: 27
Location: NH

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 9:20 am

If you have pcmcomm or freescan you can get what the PCM thinks the water temperature is at.

Watch the connections on the ECT also.

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96slowss



Posts: 845
Join date: 2010-06-09
Age: 26
Location: Halifax,MA

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sun Feb 27, 2011 9:26 am

keep us posted. ill almost put money on it being the temp sensor.. i have a couple new ones lying around just incase..
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jvette65



Posts: 111
Join date: 2010-02-16

PostSubject: Thanks.....The prize goes to all who answered CTS (engine coolant sensor)!!   Sat Mar 12, 2011 5:56 am

I got to look at the car this week.
Checked fuel pressure first : 43 psi KOEO, then shut off Ign and checked for 3 min, held steady at 43 psi.
I started the engine and watched fuel pressure, it dropped to about 40 psi but running real rough and was hard to start.
Then I checked the resistance of the new CTS (Coolant Temp Sensor -Delphi #TS10075) and it was reading about 3K ohms at ambient temp.
Then I checked the CTS in the WP and it was essentially off-scale............bingo.
Swapped out the CTS and the engine fired right up without any accelerator help and idled out nice and smooth.
For a quick check I've listed the resistance readings (from the FSM) for that CTS in case anyone runs into a similar problem:

To test the coolant sensor, unplug the wire connector and test the resistance across the two terminals of the SENSOR with an ohm meter.

The sensor screws into the water pump.

Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.


OLD Sensor:

New Sensor:


Thanks again guys !!!
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MASShole9C1



Posts: 3764
Join date: 2009-12-15
Age: 27
Location: We must not compromise territorial range

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sat Mar 12, 2011 9:49 am

I tested the CTS on the car that doesnt start when its cold or wet. It was 8.5 k ohms at ambient. Is that normal?
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sdstick



Posts: 4077
Join date: 2009-03-20
Location: Revere, MA

PostSubject: Re: Need diagnose help: '94 Caprice w/LT1 ignition prob   Sat Mar 12, 2011 9:58 am

MASShole9C1 wrote:
I tested the CTS on the car that doesnt start when its cold or wet. It was 8.5 k ohms at ambient. Is that normal?

Was your ambient 36 deg F?
Assuming it was today, the car wasnt running & wasnt baking in the sun sheltered from the wind....it sounds reasonable, yes...sorry.
Jvette switched scales on his meter but still k ohms
1st was just OMG K ohms (889000 ohms)
2nd was K ohms (3230 ohms) Presumably inside.

_________________
Steve


96BBB 28K 3.42 Bolt-ons
95BBB 100K 3.73 383 New DD...already broke the 4L60E
95 Black WB4 Hole...ee...grail
95BBB 189K 3.08 Old DD Stolen...by Matt. Cool
Whine..eee...Silver LS6
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