Surging - Team Camaro Tech
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post #1 of 18 (permalink) Old Oct 21st, 00, 07:38 PM Thread Starter
 
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Location: Dover, DE
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Hello everyone. I've just rebuilt my '89 Iroc's 305 TPI engine (my first, with help from a much more knowledgable friend). Everything on it is stock with the exception of headers, high output oil pump, hyptertech stage 2 prom & thermostat. It's been through the breakin period with the first oil change, and final valve readjustments (hydraulic lifters). The problem I'm having is twofold. First, sitting at a light idle in gear, with foot on brake (auto tranny), the idle will pickup, then drop off, then pick up again over and over between a range of about 1000 rpm (not sure the exact RPM's as the tach is off. We set the idle at ~850 via a diagnostic computer). Occasionally, it will iron itself out and idle fine, but more often than not it will keep it up.

Second, while cruising at any speed the engine will start surging. If I give it gas it stops. If I let up on the gas it stops. If I'm giving it just enough to keep a constant speed, it'll start surging again. This seems to be an intermittant problem, but it's been happening more often.

A little more history - the computer is coding with a 'engine running lean' code a few times a day. During the rebuild, I replaced the O2 sensor with a new one, didn't secure the wire and it ended up melting against the header and shorting out. Replaced the O2 sensor *again* with a new one. Installed a new fuel filter. Gas mileage went up from ~8 mpg to ~13 mpg. Used to get ~20 mpg before the rebuild.

It's been suggested to me that the computer may have been fried by the O2 sensor shortout. Any other ideas?

Car Details:
'89 Iroc Convertable, 305 TPI (F Code), aftermarket headers & muffler, Hyptertech Stage 2 PROM. Had block & heads baked and checked out & had valve job done as well as having injectors cleaned. Replaced the following parts with new ones throughout rebuild: All gaskets (of course!), cam & lifters, bearings, oil pump, fuel filter, O2 Sensor, piston rings, plugs, wires, cap, rotor, radiator, B&M transmission shift kit (700R4), shifter cable, transmission mount, battery.

[This message has been edited by miroc89 (edited 10-21-2000).]
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post #2 of 18 (permalink) Old Oct 21st, 00, 07:53 PM Thread Starter
 
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Follow-Up:

Another problem I forgot to mention is that it goes into limp-home mode on occasion. From a stop I'll accelerate and it'll never shift. If I pop it into neutral, then back in gear it shifts fine. This is something that happens maybe 3-4 times a week. Never had it do it while driving, only from a stop.

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post #3 of 18 (permalink) Old Oct 21st, 00, 10:52 PM
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Sounds like you have mess of problems on your hands. I'll assume that the t-stat is a 160 degree. You should get a "heated" O2 sensor which has two wires rather than the single wire "unheated" version. These are recommended for engines with headers and low temp stats.

Do you still have the original chip? Try running it with the original chip and 195 degree stat and see if things change.

Did you clean the throttle body and IAC valve? These can lead to problems such as you're experiencing.

Good Luck and post back.

------------------
67 Camaro LS6 454/TH400/12bolt 3.73
1989 TransAm 5.7L WS6 W/all the options

www.geocities.com/akfourme/

[This message has been edited by cardude (edited 10-22-2000).]
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post #4 of 18 (permalink) Old Oct 22nd, 00, 04:02 AM
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One other area that seems easy to do incorrectly is the TPI runner to intake gaskets. Apparently it's easy to put them on backwards which causes a pretty good vacuum leak that would give you the problems you're having.

Jody
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post #5 of 18 (permalink) Old Oct 22nd, 00, 03:28 PM
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Here is something common when the engine has been out. Check all the grounds,engine to frame ,body grounds,ect. The most important one to check is the computer grd. which is the one at the thermostat housing.

If all the grounds check out, then I am also in for putting the orignal prom and 190 stat.

Larry
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post #6 of 18 (permalink) Old Oct 23rd, 00, 04:37 AM
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just like cardude has said,

If you put a lower temp thermostat in there and Did not change the Eprom in the computer to the superchip, you screwed up right there. the computer is set to have a 180 or 195F thermostat, anything else and the computer will see the car is not up to temp.

the O2 sensor issue is this:

O2 Sensors work by sensing temperature changes in the Exhaust System, thus corrosponding with a Rich or lean condition. the best case is Move the O2 Sensor as Close up the pipe to the engine as possible. exhaust gasses can cool slightly if the sensor is lower on the pipe and cause the computer to think it is lean.

Disconnect the battery, change the thermostat, move the O2 Sensor , and Double check the Transmission knock down , and make sure the electrical is hooked up so the computer can control the lock out on the converter, this could cause the surging.

with the battery disconnected. Turn the headlights on to drain any "residual" current

reconnect the batter and start her up. the computer will load the default Eprom values. (a 88-92 should have the OBD1 system correct?) take your car for a short run of 4-6 miles , to set the computer and let the car come up to temp. If you continue to get a condition LEAN code , then check for a vaccume leak, or replace the Eprom from another car with the similar setup. or from another 89 Iroc

good luck.

The damn boogie man gets us all now and then.

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post #7 of 18 (permalink) Old Oct 26th, 00, 02:52 AM Thread Starter
 
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Ok, thanks for the replies guys. So far I've swapped out the 'stat and chip and put the originals back in. Got the same thing happening. Last night I was able to 'borrow' a new computer to put in it, and found that it did the same thing with that also. Took it through emissions again last night (first time was right after rebuild and of course it failed miserably) and it failed the hydrocarbon test at idle(limits 220, did 230's) and the CO2 test. Across the board it was an improvement over the first time, so I think something's getting better. Darn surging is still there though along with the lean code.

This morning I will be checking out some of the other things that were mentioned here. Again, thanks for the replies and I'll let ya'll know what happens.
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post #8 of 18 (permalink) Old Oct 27th, 00, 04:47 PM Thread Starter
 
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Update:

Finally got it to pass emissions. Started checking out the fuel injectors. Found that when we unplug the injector from cylinder 8 the hydrocarbons and CO2 drop immensely (from 300 to 34, 12.8 to 0.01 respectively). Also, by feeling the top of each injector we found that cylinders 2,4,8 have a strong pulse, but cylinder 6 is very weak. On the other side, 1,5,7 are strong and 3 is weak.

Coincedently, #8's wire had gotten on the header and burnt through earlier this month. It still fired, so we taped it up and let her go.

Well, it's tagged for 2 years now. Gonna check on #8 and the others this weekend.

Just thought I'd give an update.
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post #9 of 18 (permalink) Old Oct 28th, 00, 03:09 AM
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I didn't respond to injector problems as you said they were being cleaned. Were these done by a professional shop?

Take the connector off and run an ohms test on the suspect injector and while you're at it, all of them. An acceptable ohms rating is mid 12's to 16 ohms. It sounds like your injector is shorted out and allowing fuel to flow all the time.

------------------
67 Camaro LS6 454/TH400/12bolt 3.73
1989 TransAm 5.7L WS6 W/all the options

www.geocities.com/akfourme/
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post #10 of 18 (permalink) Old Oct 28th, 00, 05:52 AM Thread Starter
 
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Our local NAPA shop cleans them and that's where I had taken them to get done. On the results report they showed me, before cleaning they were no where near each other in output. After cleaning all of them except one were within 5 units of each other, which is where they said they should be. The one that wasn't was like 10 off of the others.

I'll definetly check the ohmage on them all.

Thanks again for help!
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post #11 of 18 (permalink) Old Oct 28th, 00, 05:52 AM Thread Starter
 
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Our local NAPA shop cleans them and that's where I had taken them to get done. On the results report they showed me, before cleaning they were no where near each other in output. After cleaning all of them except one were within 5 units of each other, which is where they said they should be. The one that wasn't was like 10 off of the others.

I'll definetly check the ohmage on them all.

Thanks again for help!
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post #12 of 18 (permalink) Old Oct 28th, 00, 06:49 AM
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For all injector work, I highly recommend this guy. When I went through my injector problems, he spent lots of time giving me advise that didn't cost me a penny!!!
http://www.cruzinperformance.com/



------------------
67 Camaro LS6 454/TH400/12bolt 3.73
1989 TransAm 5.7L WS6 W/all the options

www.geocities.com/akfourme/
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post #13 of 18 (permalink) Old Oct 29th, 00, 02:18 PM Thread Starter
 
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Ok, ran a multimeter on all 8 injectors today and this is what I found:

#1: 9.4 ohms
#2: 9.5 ohms
#3: 16.7 ohms
#4: 16.5 ohms
#5: 16.7 ohms
#6: 16.6 ohms
#7: 17.4 ohms
#8: 17.2 ohms

I'm not exactly sure what this is telling me (sorry guys). None of them were within the ranges you gave me, so are they all "bad" and need replacing?
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post #14 of 18 (permalink) Old Oct 29th, 00, 07:02 PM
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I am very interested to hear what you come up with on this issue. My '89 Chev 1/2 ton truck with the 350 and Throttle body is surging like you describe. It runs fine, but surges when I am just barely on the throttle to hold a speed, like on a flat road at 25 MPH. I changed the throttle position sensor, O2 sensor, spark plugs, cap and rotor, fuel filter, and injectors. No change.

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post #15 of 18 (permalink) Old Oct 30th, 00, 04:07 AM
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#3 through #8 are fine. #1 & #2 need replaced.

When the impedence of the coil inside the injectors start to excessively wear, they no longer have the resistance required to keep them closed. Once the engine is up to operating temp the problem just compounds itself.
Required impedence for those style of injectors is from 12 - 16 ohms +/- .05

<BLOCKQUOTE>quote:</font><HR>First, sitting at a light idle in gear, with foot on brake (auto tranny), the idle will pickup, then drop off, then pick up again over and over between a range of about 1000 rpm<HR></BLOCKQUOTE>

What's happening is the injectors #1 & #2 aren't capable of holding the seat closed inside the injector, so they are dribbling more fuel than the engine is asking for. Because of this rich condition, the ECM compensates. This is the surging (or "hunting" as I call it) your feeling.

<BLOCKQUOTE>quote:</font><HR>If I give it gas it stops. If I let up on the gas it stops <HR></BLOCKQUOTE> When you give it gas, the engine requires more fuel. Since the dribbling injectors are already doing that, the problem goes away, until you go back to a steady condition. On de-cel, the fuel delivery won't be noticed unless somebody is behind you, then it's whewww.

RobR, I'm not to knowledgeable on TBI, but if it was happening to me, I would look for a vacuum leak.



------------------
67 Camaro LS6 454/TH400/12bolt 3.73
1989 TransAm 5.7L WS6 W/all the options

www.geocities.com/akfourme/
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