BIG No start problem, please help

[8upZR1]

I am new to this site and Zr1's in general but have a serious sittuation and I thought maybe somebody could help me out. My ZR1 is a 1990 with just under 20,000 miles. The head gasket blew from using purple ice and so I replaced it. While motor was apart I ported the heads, intake, TB. air horn, and headers. I put the motor back together and set cams at 107.5 intake, 109 exhaust. Now the motor will not start. The starter will turn the motor, the plugs are firing in correct order, and the injectors seem to work. When checked, the plugs are wet with fuel, and there is a puddle of fuel under the open headers. I have tried different chips GM and aftermarket, fuel pressure looks perfect, no trouble codes, good compression, good intake vacuum, yet no start. Every once in a while I get a pop and a fireball from the headers but that is it. Does anybody have any ideas about this situation? I am desperate because I have tried every trick in my arsenal. PLEASE SOMEBODY HELP ME OUT.

[tomtom72]

I'd be stupid if I said I knew what was wrong.:o The crank & cam sensors are okay? the brain box for the inigition, the one on the underside of the plenum, is okay and the other one over by the A/C box? Sounds to me like it can't find the cylinder the system uses to start the ignition sequence, cyl #6 or is it cyl #1. See I told you I don't know much, sorry.:o

Maybe a call to Gordon Killabrew, foryourcar.com, or maybe call Mr. Haibeck at ZR1Specialist.com. Sorry that's all I can come up with. One of the more experienced guys would have more useful input to share with you...when they see this they'll post up.

:thumbsup:
Tom

[ZR1 MK]

I assume its an ignition issue based on your description. Wet plugs means they arent firing at all or spark is too weak. Check spark at each plug to determine if you have no spark or weak spark and diagnosis according to the manual.

[8upZR1]

the cam and crank sensors are new, so is the ignition module under the plenum. coils are msd and I run the MSD dis-4+ box. I have visually verified that all plugs are firing. There is no adjusting timing so I cant imagine it being that far off. is there any way my cam timing is so aggressive that it wont start? would the plugs perhaps be firing in the improper order if I switched the wiring harness connections that go into the ignition module under the plenum? Can't imagine i did something like but then again I cant figure anything else out. Does anyone know of a way to adjust fuel mixture @ start up without burning a chip?

[ZR1 MK]

If you are getting proper spark, you might be getting too much full. Check full pressure. Try full throttle for an extended period of time (flood clearing mode as outlined in the service manual).
Just because a part is new doesnt mean it is good, although most faulty parts will create a trouble code. Easy to check each part for proper connection, voltage, resistance etc.
110 degree is the max timing for the LT5. Any more wont create more power. Why so much timing? I cant see aggressive timing as cause of the problem, but Im not the expert in that area. Are you sure you timed and locked them in correctly?

[8upZR1]

Today's mission will be to replace all new sensors with the originals to see if they are faulty. The cam timing is accurate, I rechecked each cam after instllation to verify the timing. The cam timing I chose was based on recomendation by a highly respected ZR1 builder, MR. K. He told me 108/110 for good drag motor, `103.5/106 as most aggressive he has gone. I figured since my port work was a tad on the aggressive side I would go with cam timing slightly more aggressive than the recomendation. I ditched the secondary throttles/shafts as my motor is setup for topend power, I dont care much about low speed torque. COuld my lack of secondaries have anything to do with the no start situation? Is it possible to verify timing on the LT5 with a timing light?

[ZR1 MK]

Is your chip programmed for this modification? The prom has to be programmed for the deleted secondary system. It will search for proper function and without finding it will cause problems. Codes for sure, but you mention none. I dont know the result, but a no start might be the result. You need to check with a LT5 chip tuner.

[8upZR1]

My chip is from Haibeck, he tells me it should work without problem. Before removing the secondaries all together I had problems with the system so I had them fully opened manually and the car ran fine. I kept the secondary solenoid hooked up to the harness just to make sure the computer wasn't misbehaving. I have swapted cam sensor and crank sensor and ignition module with originals that are known to work fine and the car still wont start. I am stupified by this.

[8upZR1]

I have checked for codes throughout the process of trying to start the engine and never a single code.

[8upZR1]

I have just ran a little test that may help in diagnosing the problem. As stated earlier the car shows no trouble codes. I thought this was strange and so I unplugged the cam sensor and tried again to start the car. Obviously it did not start, however after the attempt I rechecked the error codes and to my surprise there were none. Just 12 12 12. Should I not have a trouble code if the cam sensor is unplugged? Does this mean ECU?

[Jeffvette]

Unplugging the cam sensor will not keep the car from starting. It will just not receive the sequence for corrct firing and run in batch mode instead of sequential.

Just out of curiosity, when you pulled the original crank sensor out, did you notice if you had a small shim?

[Tyler Townsley]

Do you have a service manual? Its the best place to start. Having chased a bad dis for 2 1/2 years I can understand your frustration. You need to check the crank sensor function, depending on which you have there could be too much gap. I do not remember what it should be but this is a known problem. You can put a timing light on it to see if you are in fact getting spark at #1 tdc.

My dis would give good spark at <400 rpm but start falling apart over that rpm. Finally found a dis checker that checks the whole dis system including the cam and crank signals. The tester allows you to simulate the crank and cam signals through crank and running. I put a scope on the crank signal and cam signal and they were the the same as what was being simulated. I then ran the simulation through the dis and you could see the spark fall apart on a scope and at the pulgs.

It is called an ISS (Ignition system simulator), made by OTC model # 3575. I bought mine off ebay for $130 and it should be a tester everyone doing LT5 troubleshooting should have. It can also be used to check injectors and coil/wire problems. IE put a plug in each wire, lay them on the plenum and watch the spark across the tip. Any plug with weak spark would indicate bad coil or wire. Again easy to check, replace wire or coil and run the check again.

Tyler

[8upZR1]

Yes the crank sensor has a small shim, which I kept in place on the new sensor. When I tried the old sensor to see if it worked I left the shim out and still no luck. I have put the plugs on the manifold and they all fire, nice big sparks, very pretty. I guess I will try this OTC ISS device, it sounds like a great diagnostic tool. I thought the cam sensor was used to tell the ECU when cylinder #1 is on compression stroke, for ignition timing, at least that is how Ford does it. Thanks for the input.

[tomtom72]

Hi, it would be a very unfortunate coincidence on the ECM. I have a 90 and I have a spare, good ECM that I bought...it is really a 91 ECM as I think the 90's were NLA...anyway it works in my car fine so I know it's functioning correctly...if you can't get a known good ECM hit me up & I'll ship my spare to you if you think it will help? Oh, it has a standard EPROM for a 90 in it, but you could swap your EPROM into it.

You can PM or here is my e-mail, ThomasTom72@aol.com.

:cheers:
Tom

sorry I keep posting with no answers to your situation. I'm new to EEC motors...last vette was a 72!

[Tyler Townsley]

This may help with troubleshooting the dis side:

http://www.sirgalahad.org/tyler/prototype/page09.jpg
http://www.sirgalahad.org/tyler/prototype/page11.jpg
http://www.sirgalahad.org/tyler/prototype/page12.jpg
http://www.sirgalahad.org/tyler/prototype/page13.jpg
http://www.sirgalahad.org/tyler/prototype/page14.jpg
http://www.sirgalahad.org/tyler/prototype/page15.jpg
http://www.sirgalahad.org/tyler/prototype/page16.jpg
http://www.sirgalahad.org/tyler/prototype/page17.jpg
http://www.sirgalahad.org/tyler/prototype/page18.jpg
http://www.sirgalahad.org/tyler/prototype/page19.jpg
http://www.sirgalahad.org/tyler/prototype/page20.jpg
http://www.sirgalahad.org/tyler/prototype/page21a.jpg
http://www.sirgalahad.org/tyler/prototype/page22.jpg
http://www.sirgalahad.org/tyler/prototype/page23.jpg
http://www.sirgalahad.org/tyler/prototype/page24.jpg
http://www.sirgalahad.org/tyler/prototype/page25.jpg
http://www.sirgalahad.org/tyler/prototype/page25a.jpg
http://www.sirgalahad.org/tyler/prototype/page25b.jpg
http://www.sirgalahad.org/tyler/prototype/page26.jpg
http://www.sirgalahad.org/tyler/prototype/page27a.jpg
http://www.sirgalahad.org/tyler/prototype/page28.jpg
http://www.sirgalahad.org/tyler/prototype/page29.jpg
http://www.sirgalahad.org/tyler/prototype/page29b.jpg
http://www.sirgalahad.org/tyler/prototype/page30.jpg

Tyler

[Tom]

A couple years ago I tried three different crank sensors from my local dealership and all three had the magnet installed backwards. This reverses the polarity of the signal generated by the crank sensor and the car will not start. You can tell if the new sensor has the reversed magnet by holding the magnet ends of the new and old sensors near each other, if they repel each other the magnet is correctly installed, if they attract each other the magnet is reversed.

I made a couple of jumper wires to reverse the polarity of the signal and the car would start and run with the sensors with the backward magnets. The engine had to crank longer than normal to start any time I changed out the crank sensor.

I talked to one of the service people at the dealership when I found the reversed magnets and he checked and found GM had other reports of reversed magnets.

[8upZR1]

Thankyou so much for the DIS diagnostic info. I appreciate the offer of using your ECU, maybe if nothing else works I will take you up on it. I will be going over the car today, hopefully I will make some sort of progress. While I am in the garage I will also check the magnet polarity on the crank sensor. Does anybody know what function if any the oxygen sensors play during cranking? I would think that they only come on line once the engine is running but if they are used during start up maybe I should check them out.

[8upZR1]

I have been playing with the vette all day today and have found some what I belive is the cause of my problem. I tested the spark plugs again by removing them and placing them on the plenum. Everything OK as usual. Then I cranked the car and no start. Removed the plugs again and retested them to see if the fuel on the plugs was hindering their work. To my astonishment, cylinders 1 and 6 and 2 and 3 fired while the others barely produced spark. I cleaned the fuel off of the plugs and then retested. This time 4 and 7 and 5 and 8 did not spark at all. In all previous tests they gave good spark as did the others. What I really do not understand is that the way I have the MSD box set up 1,6,4 and 7 are run by channel 1 and 2,3,5,and 8 are run by channel 2. I then unplugged the MSD and still the same deal, no firing on 4,7,5,and 8. So it is not the MSD. But what could it possibly be? Wiring? Ignition module? Tonight I will replace the ignition module under the manifold with a spare I keep around. It seems strange to me that it could be the module because I replaced it about a month before the head gasket failure and everything was running top notch. If anybody knows what effects only 4,7,5, and 8 please let me know.

[8upZR1]

Well, that was a waste of time, all plugs are firing again but no start up.

[tomtom72]

On the O2 sensors, I don't think that they are part of the system until the "closed Loop" cycle has been reached. On my scan tool they don't send any data till the system gets to "closed loop".

On the ECM thing...it's here & let me know if you want to try it!

[ZR1 MK]

Keep in mind, a proper spark is much harder to create under compression. At this stage, investigating Tylers senario may be the best thing to do.

[8upZR1]

I went through the diagnostic procedures that Tyler's pages outline. At least all of the ones that I could do without special equipment that I do not have, such as oscilloscope. The pages say that if spark is present then there is no reference signal from the ignition module and it must be replaced. I have tried a brand new in box, never used ignition module and no dice. My other ignition module only has about 10 hours of operation on it. I have noticed though, that when I try to start the car with the MSD hooked up, the light on the MSD indicates an interuppted signal. However, instead of staying on, the indicator begins to flash showing that the system is operating properly. I have checked for continuity between the ignition module wires and the ECU and everything looks good, all harness connections look solid. I noid lighted the injector harness and everything looks peachy there. I am dumbfounded, however leaning towards suspecting the ECU.

[Tyler Townsley]

Remeber less than 400 rpm all spark timing is done in the dis module. That was why I bought the tester. I already had an ecm I knew was good and it made no diference. If you are still stuck next week I can add a scope to the ISS tester and I have a good 90 ecm somewhere. Another thing to check is pull the eprom, clean the contacts. and make sure it is seated properly.

Tyler

[8upZR1]

But I am getting sparks, and I know that these modules are good, so I am thinking that the sparks are merely coming at the wrong time. The ECU apparently handles the advance so my guess is ECU. Maybe its just a chevy thing.

[Tyler Townsley]

But I am getting sparks, and I know that these modules are good, so I am thinking that the sparks are merely coming at the wrong time. The ECU apparently handles the advance so my guess is ECU. Maybe its just a chevy thing.

Not true. You need to read this page to understand the spark operqtion.

http://www.sirgalahad.org/tyler/prototype/page17.jpg

At start the ecm is signaling the dis to operate in bypass mode, which means the ecm is out of the loop. It would very unusal for you to have 2 bad dis modules but that is what happened to me. The one module would generate spark below 400 rpm but fall apart above that. Also check all your grounds especially those pretaining to the ecm ignition modules. Ohm them each to ground

Tyler

[Tyler Townsley]

This may help trouibleshoot the ecm:

http://www.sirgalahad.org/tyler/misc/90ecm1.jpg
http://www.sirgalahad.org/tyler/misc/90ecm2.jpg
http://www.sirgalahad.org/tyler/misc/90ecm157.jpg
http://www.sirgalahad.org/tyler/misc/90ecm158.jpg
http://www.sirgalahad.org/tyler/misc/90ecm159.jpg
http://www.sirgalahad.org/tyler/misc/90ecm160.jpg
http://www.sirgalahad.org/tyler/misc/90ecm161.jpg

Missing last page will post it when I get my trailer back.

Tyler

[Z Factor]

I am new to this site

Hello and welcome tp the forum.:handshak:

I see you have been getting a lot of good advice as usual.

Nice posts TT, worthy of some reputation points.:thumbsup:

:cheers:

[8upZR1]

Thankyou Tyler for the ECM diagnostic material. I will look it over tonight and hopefully put it to good use tomorrow.

I was wondering if by some cruel chance of fate, that my cam timing somehow slipped on one bank, that this could be the cause of my problem. I rechecked the timing when I was done torquing down the cam bolts but I am some how second guessing my work now. If one cam slipped on the sprocket say 50 degrees or so would the motor not start? Would the other side of the motor not operate correctly? If a cam slipped that much would I not have valve piston issues? I am absolutely positive that the cam timing is spot on and that it has not moved but this no start deal is driving an urge deep within me to tear the motor apart and double check just so that I can sleep more soundly. But then another part of me says I will commit suicide if I tear into the motor, find the cam timing OK, have to do all that work again and still have this no start issue. Maybe I am having issues. If there were a cam that could possibly have slipped it would 100% definetely have to be the drivers side intake cam, as a small 15 degree segment of the snout of the cam was broken off during the install. I had the timing plate pinned onto the gear and wanted to see what the cam timing would be if I retarded the cam all the way with only the play in the system. My thought was that if the bolt failed somehow then the cam would retard to the end of the adjustment range within the hole I used for the cam timing pin. When I manually retarded the cam to the end of the adjustmewnt range a happy little peice of the cam snout broke off. It was half radius half flat. I just reset the timing to where I desired it to be and then torqued the cam bolt down, figuring it would be strong enough to hold the timing. I do this all the time for DOHC Ford modular engines that are used for drag racing, just leave out the keyway and torque the bolt down. It lets you have more adjustment of the cam timing then the single keyway will allow. I have never had a slippage issue and these motors rev to 9K.

I was thinking back to when I took the motor apart and was thinking that I might have just maybe dropped the ECM onto the floor by accident. Are trhese things shock proof? Most likely I did not drop the thing but anything is possible.

[8upZR1]

I have just tried an ECU from a ZR1 that works, and it was not worth the effort as it had no effect. This problem has me totally baffled.

I was wondering if anybody who has O2 sensor or A/F ratio gauges in there car could tell me what they read when the car is cranking?

[ZR1 MK]

If there were a cam that could possibly have slipped it would 100% definetely have to be the drivers side intake cam, as a small 15 degree segment of the snout of the cam was broken off during the install.

What cam bolts did you use?
What torque tool and method did you use?
What exactly is the extent of the cam damage?

[8upZR1]

Bolts from Haibeck, method used was the one outlined by Haibeck and also by Milstead. The extent of the cam damage? When you look at the cam from the front, you see the snout is a 300 or so degree circle with a flat portion, to keep the timing plate from rotating. The very tip of this snout, about 2 mm deep, and part round, part flat broke off of the cam. Radially thie broken piece probably spans 20 degrees, if even. I was amazed as I was not giving the cam hardly any torque. To turn the cam at this point I was using a 19mm box ended ultra stubby wrench designed for tight places. It is maybe 4 inches long, so the torque I was applying was absolutely minimal. I figured the damage was irrelevant as the bolt and washer do not touch this part of the cam when they are torqued down.