I just picked up a 1986 sport coupe with the 2.8 and 700r4. She has 84,000 original miles. Last week i replaced the oil pan gasket, water pump, and timing chain. The issue i am having is whenever the car is cold and i give it a small amount of gas to accelerate, it will pop pop out the intake and hesitate a little, then even out. The timing chain had a lot of slack and cracks in it, so im glad replaced it. The timing is spot on and at 10 degrees btdc.

I also set the tps to .54 volts. Once the car is warmed up it runs fine and has no issues. It only pops and bogs when cold and under very light acceleration. If i give it more gas, maybe 1/2 pedal, it wont pop and accelerates fine. If anyone has any ideas of what could be wrong it would be great.

EDIT: The car had the same issue with the old timing chain, which is why i replaced it.

 

No check engine light??

You happend to notice what the exhaust smells like? Does it smell overly rich or lean?

 

Sounds like a lean pop, the only thing that can cause it is, ONE- the mixture is getting to lean at that spot or, TWO- something is causing one or more of the cylinders to fire before the intake valve is closed.

Look for vacuum leaks when cold, pull plug wire to isolate cylinders, move injectors around, do cylinder compression test, also make sure all injectors are firing when cold.

 

It had a check engine light on when i first got it, but it was a code 34. I replaced the MAF sensor and the light went out.

 

Check the plugs and see if theres any tan on them at all or if the pig black. Im guessing lean pop also.

When its warm does it idle smooth??? If so i doubt its a vac leak but who knows best way to tell is to start going crazy and shooting carb cleaner on every place there could be one and listen to the car idle. Youll know when you found it if there is one. Or you could just hook up a vac guage and see the inches of hg and see if its steady also at idle.

 

Check the fuel pressure.
Have your injectors cleaned.

 

Where should the fuel pressure be around? Im going to pull the plugs either tomorrow or Wednesday when im off from work. As far as vaccum leaks i sprayed everything with carb cleaner the other day and i didnt find anything. It idles pretty smooth at 700rpm when warm.

 

Figured I'd post some pics of the car:





Old timing chain:

 

Good readings are 35-42psi running, 42-48psi w/ key on, engine off. It should hold the fuel pressure for a long while.

 

Agree with the above. Check the fuel pressure. Could be something as simple as a plugged fuel filter.

Wow thats one bad timing chain. That was definitly a good thing to replace regardges of it causing a problem or not.

Nice car though man, looks to be in good shape.

 

The previous owner had all the fuel lines replaced, aside from the return. He also said he replaced the fuel pump. All the lines under the car are new including the fuel filter. Im gonna test the fuel pressure and see what i get.

 

I just checked the fuel pressure. Its at 38 psi while running, and 42 psi with key on engine off. Its also still holding 42 psi after sitting for 5 minutes.

 

The popping is getting worse and worse the colder it gets. This morning it would pop about 5 times every time you come off a dead stop. The car is fully warmed up now and its running absolutly perfectly.

 

You might have a coolant temp sensor thats reading wrong at cold temps. Ohm it when its cold.
Clean your maf sensor.

 

I just tested the sensor with the car running, fully warmed up. The highest the ohms got to was 416.5 then it started dropping.

 

I changed the sensor and connector. The connector was cracked and the prongs were broken away from the housing. I had it sit for an hour and it still gave a little pop on acceleration. Not sure what to check next.

 

Did you clean the maf sensor yet?
You might have dirty injectors. Did you do anything with them yet?
I guess i'd start by checking the ign. timing. A new timing chain will change the ign. timing, esp. if it was adjusted with a loose timing chain before. Follow the instructions on the emissions label.

 

The MAF sensor is brand new. I set the timing again after installing the new timing chain. Its at 10 degrees BTDC. I set it with the computer advance disconnected. I also pulled all the plugs today and every one looks fine. I didnt do anything with the injectors yet.

 

Well i just pulled the distributor cap and all the metal contact points under the rotor are covered in rust, and the pickup coil has a small crack in it. Hopefully this is the issue. Im gonna replace it and see whAt happens. This would also explain the occasional hard starts ive been getting.

 

Well heres a recap...

Timing chain was replaced and timing is set perfect.
Fuel pressure is good at 38 psi running, 42 psi key on engine off.
Plugs were pulled and are all fine, as well as cap, rotor, and plug wires.
Replaced engine coolant temperature sensor and connector.
And today i replaced the rusty old distributor and re set the timing.

And it still pops out the intake, and gives hard starts some times when cold.

Here is the old distributor:


Im really not sure where to look next. If anyone can think of anything else i should check, i will be very grateful.

 

Did anyone mention the fuel injectors yet? Clogged one could cause a lean pop i suppose.

FYI if you have to replace any more parts such as the dizzy like you just got that are somewhat exspencive. I have tons of that stuff in good working order for very cheep.

 

Should i just get some fuel injector cleaner and put it in the tank? I didnt think it was an injector issue because once its warmed up it runs fine, but it would still give a hard start once in a while.

 

You could try that i suppose but im not sure if it will work as well as if you take them out and test them.

You did look for a vac leak before correct?

 

I looked for vacuum leaks with carb cleaner but didnt find anything. The valve covers are leaking pretty bad so i ordered a complete gasket set and im going to change the upper and lower intake gaskets. Im also going to adjust the lash on the rockers and see where that goes.

 

Theres no air or pressure coming outta the oil fill spot on the valve covers? Just take the cap off and start up the car and put your hand over the hole, reve it up a little too and feel for air pressure. Not that I think thats a issue but that will cause a lean pop.. believe me I know that....lol

 

Theres no air i can feel coming out at idle, but i can feel a tiny bit when i rev it. The idle also drops a little when i removed the fill cap.

 

Well i borrowed an obd1 scanner from a co worker and came back with a code 13 for the oxygen sensor. There was no check engine light on though which is weird. Im picking up the sensor and a set of plugs, so well se how it goes.

 

Well 02 sensor and plugs are in, same issue...

 

be 100% sure the dizzy hold down bolt is tight, it only has to move a hair to cause a problem.

 

Hold down is definatly tight. Im gonna recheck the timing when i get home. If it still does it, hopefully adjusting the rockers will fix it.

 

o2 sensors fail to make the car rich. So that code 13 isnt the main issue on why its having that lean pop anyways.

You did take off the electronic timing wire when setting in the timing to 10*btdc correct? Then turned the car off, then put the wire back on, reset the ecm, then fired her up??

All I can think about is that one of your fuel injectors is clogged up and causeing a lean cylinder?? How do those plugs look if you idle for say 10 minuets and then pull them all out?? Is there a noticible color difference in any of them?

 

Yes i disconnected the advance wire while setting the timing. There is also no difference in the plugs, they were all light gray on the tips.

 

Damm really got me stumped. Did you ever toss on a vaccum guage on the cars intake to get a good reading on the vaccum of the car?

Doesnt tick does it??

 

Well i have some new information. Driving home today with the radio on i noticed it pops on decelleration when fully warmed up. So when cold it pops on acceleration, but when warmed up it only pops on decelleration.

 

Does it run better if you disconnect the MAF meter? Try starting it when its cold and unclip that MAF first, see if that helps? Im just guessing here on what else could cause that lean spot else then the injectors because that will take you a good hr just to get them off for the first time.

 

Its in deacell mode when you let off the gas which is lean as crap anyways but thats suppose to happen.. but just not pop in the process....

 

Yes i disconnected the MAF sensor today but it still popped. When i change the valve cover gaskets next week ill check the injectors.

 

Ok Maf is ok then. keep us up to date. Im curious of what the problem is. Exspecially since it pops under deacceleration.

 

I think i MAY have found THE problem. Well regardless its a problem either way. I noticed driving home tonight that the car was idling rough jumping from 700 to 500 rpm and hesitating. When i got home i saw that number 5 spark plug wire was arching big time from the plug heat shield to the block.

I checked every wire with it running in the dark and every cylinder has a small amount of arching from the plug heat shields to the block. I removed the heat shields as a test and the arching has stopped, and the idle isn't jumping anymore. Ill post an update tomorrow when i take the car out with it cold. Hopefully the popping is gone.

 

The wires or plugs are bad, spark will seek ground with the least resistance, if it’s easier for it to come out of the side of the wire.... something in the chain is wrong.

 

The plugs are new. Im gonna pick up a set of wires.

 

doesn't matter if the plugs are new, new parts aren't always good parts.

#! Rule in working on cars.

 

I picked up a set of wires. Hopefully it fixes the problem. I changed the plugs a few days ago but not the wires, so i figured id start there. If it still archs ill exhange the plugs. Ill keep you updated.

 

This couldn't be more true.... I went through 3 part store MAF's trying to diagnose a backfire. Checked every single sensor on the car replaced quite a few being the car sat for so long as well. Read about how crappy the auto part store MAF's are and went on ebay and found a NOS MAF for a firebird for 60 bucks. Cut the elbow off of it to fit my camaro and installed it and I haven't had a backfire since.

 

Haven't had power for a few days from the storm, but now that its back up and running i have some updates. I replaced the old plug wires and all the arching went away. It didn't pop as much as it did before, but would still a little bit when cold.

Yesterday i had to wait in line 2 hours to fill her up, and got premium because they were all out of regular. Well Im glad i did, because with premium gas i get no popping at all, absolutely nothing. Im not sure why it would pop with regular, i would think that these cars would be able to run 87 with an issue, but being 92 fixed the issue, im going to continue using that. It also idles smoother when warm with the higher octane.

I also got my gasket set from rockauto today, so Im going to replace all the upper gaskets, and check out out the valve lash. Ill keep you updated.

 

Try ohm testing the injectors when you get access to them. Sometimes the shorting out issues are temperature sensitive. That test doesn't prove they're good but it's something to check while you're in there.
I don't know if your 86 would have come with Multecs from factory, but they often get used as replacements regardless so it could have them.
I don't trust old injectors much and a set of flow-matched refurbs helped out a stumbling issue on my 2.8, but I don't see any solid indication your injectors are bad. I'm not sure what to make of the fact that premium fuel fixed it.

I think the reason it runs better at more throttle is because you're putting it into power enrichment mode.

 

I started pulling the valve covers and found some things. The injectors look shot so i am going to replace them. Also the rockers need adjustment pretty bad. I can easily spin every push rod with my fingers, and some have some have slight up and down movement.

If anyone has a set of used injectors for sale i will buy them. Heres some pics of the injectors:






Also the reason the check engine light wasn't working was because of the bulb. I swapped in another cluster with a tach shortly after buying the car, and i didn't realize the bulb was bad.

 

I Pm'd you about the injectors. Mine ohm out fine and ran fine last time they were used (1 month ago)

If you get my injectors I sugest getting 3 sets of these o-rings so that there will be 12 in total. You will take the old off and then lube the new ones up and toss them on. The o-rings I have on the injectors arent bad but for a extra 12 bucks from autozone you ensure you have a nice new seal.
http://www.autozone.com/autozone/par...580396_21063_0_

What you wana do with those pushrods is to make sure the lifter is all the way down(valve closed) then tighten the 15mm nut till there is "o lash" basically you can just barly spin the rod with your finger tips. Then "it" says to tighten them 3/4 turn more IIRC but I just tighten 1/2-5/8th of a turn. Id rather they be a hair loose and need tightened then have them get bent because I over tightened them. Obvously you can do more then one at a time since multiple valves will be closed at the same time. But you get the idea I think??

 

i made some good progress today. Got everything apart, cleaned and back together. I replaced the valve cover and intake manifold gaskets, and set the valve lash. Everything looked good, no bent push rods or anything. Everything is just about done, just need the injectors and she'll be ready to fire up.

 

Ok bud here ya go they'll be there mid week. Hope thats the issue and your good to go!

O rings are good enough if you cant get some fresh ones. No cracks or anything. The injectors are really quite new considering. 20k miles on them.



All ohm at 12.1-12.2. Good to go/



Funny thing is the last set of stock injectors I sold was to a kid that had similar issues and when he got them the car ran like a champ...lol It was to greencamaro but hes not on here much anymore.