Motors eating coolant, and bad miss

[1fun281]

I have a 99 gt with underdrive pulleys k&n cai, offroad x with flowmasters, and 24lb injectors. My motor when starting up cold, and sometimes just when it feels like it it misses around 2k rpms, and at an idle drops to about 600 then comes back up. We have also found that my motor is eating coolant.
My question is does anyone know any possibilities of this problem is mostly the miss.
We changed the EGR, IAC is good, New MAF calibrated for the 24lb injectors.
Another question is are these problems related could one be causing the other?
Any help would be greatly appreciated.

 

[eliteJAE]

Have you tried a compression test yet? Any white smoke coming out the exhaust? Could be leakng coolant out the intake onto the plugs which could cause a miss every now and then, or you could have a somewhere else, like in the heads. I had a blown head gasket, ate lots of coolant, etc. You having any overheating issues?

 

[1fun281]

Im having no overheating issues at all, daily driving and flooring it no overheating and no visible white smoke. At all.
We have been trying to chase this problem but were kinda getting stumped about the miss, we thought it was possibly the EGR because it seems the miss goes away right about when the motor is warmed up and goes into open loop, so we figured maybe the egr valve was sticking but nope it didnt help when we changed the egr.

 

[wmburns]

How do you KNOW the IAC is good? The drooping idle is frequently the IAC or a vacuum leak.

Is the MAF clean? Any DTC's?

Have you inspected the spark plug wells looking for water/coolant? If there is any moisture in the holes, this could ground out the spark causing a miss. The coolant leak could be external and a source of moisture (and the reason the car is eating coolant). Blow the spark plugs holes out with compressed air.

Note, if the spark is leaking out of the boots, this can damage the insulation. So even if the moistue problem is fixed, the miss may not go away.

Consider pressure testing the cooling system. May make it easier to locate the source of the leak.

I am confused about your comments on "open loop". Normally "open loop" occurs during starting, WOT, and sensor failure.

The EGR is disabled during open loop operation. How are you monitoring open loop? Do you have an ODB2 scanner to monitor other operating data?

For that matter, if you want to completely rule out an EGR problem, disconnect and plug the vacuum line to the EGR value. If the idle problem improves, this means the EGR system has something to do with it.

The disabled EGR will not affect how the car drives, but it will throw a DTC code. That's OK since we know its for testing. Report the results.

The best way to resolve problems is to work through the most likely causes and then work towards less lilkely causes. But if steps are skipped along the way, chasing wild geese is a real possibility.

 

[DJ Fury]

Aye I'm a bit confused as well... There's nothing to monitor in open loop mode. Open loop is a constant voltage. Closed loop occurs when the motor heats up to operating temp and the engine starts making A/F adjustments based on inputs from various systems. The voltage should vary during closed loop mode not open loop.

 

[hotrodredneck]

most importantly, if the engine is "eating" coolant, I would worry about that issue before a miss issue.

 

[the98stang]

do you have the old plastic intake manifold with the plastic coolant crossover? If you do, it could be cracked and leaking coolant into the cylinders or elsewhere. Easy test would be a leak down/pressure test. If the intake is cracked and coolant is getting into the cylinders it may cause the spark plugs to foul therefore causing your idling issues.

 

[1fun281]

I already have a pi intake, with the aluminum crossover,but it wasnt stock so im wondering if whoever put it on could have screwed sumething up, because there were a few problems we had to fix with the car

 

[the98stang]

I already have a pi intake, with the aluminum crossover,but it wasnt stock so im wondering if whoever put it on could have screwed sumething up, because there were a few problems we had to fix with the car

you have to do a leak down/pressure test to find out where the coolant is leaking from

 

[1fun281]

ok thanks for the help i guess my next move will be a leak down test sorry for the newb post