Hard to start, then backfiring

[UNGN]

Got my motor back in finally, but am having some "doesn't want to run right" problems.

It's very hard to start (like when you advance the timing on an old car), then when it does start, it backfires constantly (You can see the the backfire in the exhaust) It doesn't want to idle, and when you try to rev it up, the popping gets worse.

Motor has new timing chain, heads, injectors (55# that are new to me, but not new), New ECM, new spark plugs @.035, new plug wires. Everything else worked fine when the car was parked.

Cam sensor has been set properly (did it twice to be sure), I have spark and I'm pretty sure the at least some of the injectors are firing.

I did a compression test on one side of the motor and I got 2 145's and a 140.

It's got me baffled and I'm open to suggestions.

Thanks for the help

 

[TurboDave]

Please don't take this wrong, but... How do you know the cam sensor is set properly??

Can you describe in detail how you installed and set it?

 

[UNGN]

Originally posted by TurboDave
Please don't take this wrong, but... How do you know the cam sensor is set properly??

Can you describe in detail how you installed and set it?

I rotated the crank to 1.45" past the zero mark. The compression stroke was verified by screwing a hose into the #1 hole and watching for it to blow air when the crank was turned.

Once the crank was set, I put the cam sensor in place. Backprobed the middle wire to verify 7 volts. Rotated the cam sensor clockwise until the volts dropped to zero, rotated it back counter clockwise until it just got to 7 volts then bolted it down.

Is that right? I was going off memory. I thought I may have set it wrong when it didn't start the first time, so I tore it apart and set it again to be sure.

 

[zam70]

1. Measure on a piece of masking tape and mark it at 1.45" and tape it to the Balancer at 0 degrees.
2. Bring #1 to TDC and then grab the intercooler fan and rotate the motor to your mark (25 degrees ATDC). This takes a little patience and muscle. You can try bumping it with the starter, but I'm never very successful at that.
3. Back probe the middle wire of the cam sensor (marked B and normally blue) with a voltmeter. Turn the key ON, but leave the engine OFF.
4. Loosen the sensor with a distributor wrench or a wobble socket and extension.
5. Rotate the sensor full CLOCKWISE. The voltmeter should read 7.5+ volts.
6. Slowly rotate the sensor COUNTER clockwise until the voltage drops.
7. Secure the sensor at the instant the voltage drops.


this is from gnttype.org.

Sounds possibly like valve timing to me.

 

[UNGN]

Originally posted by zam70
16. Slowly rotate the sensor COUNTER clockwise until the voltage drops.
7. Secure the sensor at the instant the voltage drops.

hmmm.....

I rotated the sensor clockwise until the voltage dropped. I think I found the problem I'll give that a shot. serves me right to rely on my feable memory.

 

[TurboDave]

Thanks ZAM, you beat me to it.

UNGN caught the difference

 

[Chris Taylor]

You both beat me to it.

I know a guy that forgot to install his new chip following a larger injector change. His car was doing the same as you mentioned. I know you had your ECM and chip modified but I thought I would mention it. He went over everything five times and I mentioned to him if he had changed the chip. I could tell from the look on his face he forgot to change out the chips.

 

[UNGN]

Well... I set the cam sensor properly this time and it still doesn't start.

Swapped ECM, Changed chips, still nothing but hard starting and intermittant popping while holding the throttle open at 2000 RPM. I verified the Plugs wires are right and that the injectors are hooked up properly.

Have 135-145 lbs of compression in 5 of 6 cylinders (haven't checked 6), which is what I would expect givien it's got nearly 100K miles on it.

Spark plugs have black soot on them but don't appear wet.

Fuel pressure is set at 40 psi with a JL 20 degree and 116 octane chip.

Anyone have ideas?

 

[blackbuick87]

I dont know, maybe there was a mistake when they altered your ECM? Is this consistent with what it would do in "limp home" mode?

UNGN I know it would be a PIA but maybe you should start the car with the old inj/ECM, since that is the only thing you changed from before

 

[Chris Taylor]

I would start look at what you changed out. Like BB87 said, start with the ECM and injectors. This sucks I hate you are having this problem. Don't give up. I am going to sleep on it and get back. Keep us posted.

 

[striker_29]

I sure dont know, sounds like you have covered most everything. I dont think you mentioned your crank sensor, does it check out ok? Just trying to throw something out there, good luck bud.

 

[325DR]

Even though the cam sensor is set properly, are you sure the cam sensor is OK? Once your car is started, disconnect it and see how it runs. After going through a whole list of things (speding a LOT of time and money), I finally decided to do this to my car, and sure enough, thats what it was.

 

[Intercooler]

Originally posted by UNGN
Well... I set the cam sensor properly this time and it still doesn't start.

Swapped ECM, Changed chips, still nothing but hard starting and intermittant popping while holding the throttle open at 2000 RPM. I verified the Plugs wires are right and that the injectors are hooked up properly.

Have 135-145 lbs of compression in 5 of 6 cylinders (haven't checked 6), which is what I would expect givien it's got nearly 100K miles on it.

Spark plugs have black soot on them but don't appear wet.

Fuel pressure is set at 40 psi with a JL 20 degree and 116 octane chip.

Anyone have ideas?

Just my opinion here but with the stuff that happened prior you may have fouled the plugs. I would pop some new ones in and try again.

 

[Iceman]

Did you find out what is going on?

 

[UNGN]

Originally posted by Iceman
Did you find out what is going on?

I'm pretty sure I've figured it out. I'm going to thrash on it tonight (hopefully) and tomorrow and see if I can get it going. Sufice to say I made a bad selection of parts when I put the car together, grabbing something from a box, rather than going to the auto parts store like I should have. I should have it running soon enough. If Not, I'll be back