DOHC wizards

Emc209i · Post by **Emc209i** » Sat Apr 14, 2007 3:59 pm

Hi, I just killed it finally. The car is a 1988 Fiero with a '95 LQ1. Recently the Cam sensor has been throwing a code and and the motor is Jerking violently when I try to feed it more than 35% throttle in 1st gear. The problem isn't as bad when I start in 2nd and give it a good run, but it still jerks around down low. Also something to note: after throwing the cam sensor code is sometimes also throws a Crank code. When the jerking gets violent enough it blows the INJ fuses. I put 25 amp fuses into the slots to prevent fuse genocide, but the only noticeable result was more bucking and jerking in start off rather than blowing a fuse. Every time the fuse((s) , inj 1 or 2) would blow the injectors would not squirt and the motor would just spin and not crank. If at a good speed when they blew, the motor would loose all power and come to a stop. This problem has been getting progressivly worse.

So today I put a computer on the ECM and was monitoring the symptoms to get a better Idea of what was going on. As soon as the bucking began it threw the Cam code and shortly after the Crank code. I was testing second when I gave it a really good run and the motor died. I reached down and replaced the blown INJ 1 fuse (which was blown) but the motor will still not crank now. I have checked all fuses and all are good. The motor throws a constant Cam sensor now. I dug the cam sensor out of the block and it looks fine other than being hot. The wires all look good until they run into the harness behind the engine and the firewall. Also something of note, the injector and cam wiring run together in the same tail. I pulled the ECM and checked C connector pin 10 (cam sensor) and the pin is fine.

So what's the problem? Would the engine not start at all if I finally did the Cam sensor in. I though it would crank but run extremely rough. Could replacing that sensor fix the entire system or do you guys think it may be a short in the harness somewhere? When we finished the harness we made sure the harness had no shorts or weak points but that doesn't mean one hasn't developed. My main question is will the cam sensor prevent the motor from cranking.

I abandoned the car in the campus parking lot and I have no means to lift the car so I can get under it to check wiring.

Please help.
-Paul

Series8217 · Post by **Series8217** » Sat Apr 14, 2007 6:23 pm

Are you sure you're talking about the cam sensor and not the crank sensor? You mentioned pulling it out of the block.. but the cam sensor is on the front cam carrier, not in the block.
It should run without the cam sensor, but it can't do anything without crank position sensor. Does the tach move when you turn it over?
Sounds like you might have bad wiring or a faulty ECM that's shorting its injector drivers periodically.

whipped · Post by **whipped** » Sat Apr 14, 2007 6:30 pm

blowing injector fuses means your injector 1 hot +12 line is getting shorted to ground. Check the wiring harness for frays, or pinched wires.

Could also be shorting out against the cam sensor which could be really bad for the ignition module/ECM depending on where it goes

Emc209i · Post by **Emc209i** » Sat Apr 14, 2007 6:48 pm

I pulled the Cam sensor on the top of the cam carrier. I can't get to the crank sensor without some sort of lift.

It may be a possibilty that the engine smashed the harness when jerking around. I need a multimeter SO BAD. I guess I have work cut out for me tomorrow.

More input is WELCOME.

The Dark Side of Will · Sat Apr 14, 2007 7:10 pm

How can we help you diagnose things if you don't have the right tools to get the necessary information.

Put the right fuses in the INJ locations before you burn your car to the ground.
Get a multimeter.
Get a service manual.
-Follow the trouble shooting tree for the cam sensor code
-Follow the trouble shooting tree for the crank sensor code

I KNOW that these tools cost money. If you can't afford them, then sell your Fiero and buy something that isn't modified because that's the only way you stand a decent chance of not needing troubleshooting tools.

Without the proper tools, you (and by extension we) are just acting in ignorance and making WAG's about what *might* be wrong with the car, NOT figuring out what IS wrong with the car.

Emc209i · Post by **Emc209i** » Sat Apr 14, 2007 7:58 pm

"Without the proper tools, you (and by extension we) are just acting in ignorance and making WAG's about what *might* be wrong with the car, NOT figuring out what IS wrong with the car."

Then by implication your not going to be my little test monkey and start spitting out possible solutions. :rotflmao: Will, get real.

Besides being an ass, thank you for your help.... oh wait you didn't.

I'll be pulling the harness off of the motor tomorrow to check for shorts and properly diagnosing with a multimeter.

Here is what the ECM was reading shortly after the motor cut out:

TPS 0.47 volts
Injector Pulse 21.1 mS
Cam Pulse N/A
Canister purge N/A

Unfortunatly the Diagnostics computer does not measure the cam and crank voltages.

I'll be able to do that tomorrow. Whipped thank you I'll be checking that tomorrow. Series 8217 the tack reads 500 rpm when cranking. The wiring may be the culprit as the ECM seems fine. If the ECM is bad is it the prom or the board that prom is plugged into? Thank you ppl who are trying to help. Yes ignorant WAG's about what *might* be wrong are appreciated. Please feel free to share.

Jinxmutt · Post by **Jinxmutt** » Sat Apr 14, 2007 8:11 pm

21.1 ms injector pulse?

whipped · Post by **whipped** » Sat Apr 14, 2007 8:12 pm

I don't know if it just started doing this or what, but I remember something similar happening when someone pinched the injector harness between the engine and transmission bell housing after an engine replacement....

p8ntman442 · Post by **p8ntman442** » Sat Apr 14, 2007 8:12 pm

while will may have come off wrong in this thread, he is a very knowledgeable guy. We recently got a rash of shit from a parts shotgunner for trying to help and not "guessing the right part to shotgun first"

Its good you had a computer hooked up to the thing to help diagnose it, thats a good start. Now as will said you need to rely on the proper tools to diagnose the situation.

Obviously if your blowing injector fuses, but not imediatly, you are suffering from an intermittent short. If the cam sensor and injector hot wires are close to each other, Like you said they were, you already know what is most likely the problem.

re-read will's post with an open mind and extract only the useful information he provided, its exactly what you need to do.

*********disclaimer, I am not sticking up for or apologizing for Will. He's a big boy he can act as he wants.

whipped · Post by **whipped** » Sat Apr 14, 2007 8:12 pm

Jinxmutt wrote:21.1 ms injector pulse?

kinda long, eh?

probably realized it was dying and tried to save it

The Dark Side of Will · Sat Apr 14, 2007 8:24 pm

Emc209i wrote:Besides being an ass, thank you for your help.... oh wait you didn't.

I offered help. You just don't understand it.

It's good that you at least have access to a multi-meter. Good luck.

Emc209i · Post by **Emc209i** » Sun Apr 15, 2007 12:03 am

Sorry Will, I was pissed from working outside and not getting it fixed, then walking a mile back to my dorm to log in and get a reply like "go sell your car kid because you don't have 'real' tools." The car was built in a garage with more than $30,000.00 of tools at our disposal, and the engine was built "right", we went to great pain to be sure of that. I'm away from home and without any of those tools and yes I know that I need them.... duh. Sorry to come back at you but I need to get some advice from some of you guys who understand these things better than I do before I start ripping it apart to pinpoint the exact problem. I also do not have a spare battery to sit there and crank over and over and over again to test stupid things that the service manuals recommend. But if there are no ideas then I would have had to resort to that wouldn't I.

Thank you all for the help. I believe it is as you have all said a short, I hope so anyway. Thank you.

Emc209i · Post by **Emc209i** » Sun Apr 15, 2007 12:09 am

21.1 ms injector pulse?

yes that is the reading. Could this be indication of a short in the injector harness?

Series8217 · Post by **Series8217** » Sun Apr 15, 2007 3:35 am

Nah, that's the pulse that ECM wants to see. If there's a short the ECM isn't going to know.
The wiring to the injectors is not very long or complicated. Trace it. All of that wiring should be accessible from up top. Injector power comes from the fuse box in the car, goes up to the C203 to one or two pins, then out through the firewall to the mini-harness connector. The wire(s) run from there to a junction where it splits into 6 individual wires, one for each injector. At each injector there is another wire that comes back into another junction of 6 into 1, which goes through the mini harness connector and to the ECM.
The wire up to the injectors should be pink or pink with a black stripe. The wire coming back from the injectors and going to the ECM should be blue.