skyhawk50

Recently bought a 1988 that hadn’t been run for 7 years. The PO flushed and cleaned the fuel tank, blew out the fuel lines, replaced the fuel filter and installed new injectors (SAC City receipt found). Car starts hard and won’t idle and backfires. Do to the cold temps I haven’t been able to spend a bunch of time in the garage. Not really sure where to start. I used the search feature on the forums and it looks like could be the MAF or IAC ?? Not sure if it could be a timing issue or something else. Could be multiple issues. Found some empty boxes for various seals ( plenum, etc). PO not too knowledgeable (I believe he had a friend do most of the work). Open to ideas or if anybody knowlegeable in the area (Central PA)
I’ve owned several L98’s and an LT1, but never ran into this issue. ( yep, I’ve replaced several Opti’s on the LT1’s).
Thanks in advance for any help.

Red 91

Check fuel pressure

Purple92

OK - Based on what you describe - it could be literally - anything...

So - IMHO - start with the basics. Pull the plugs and do a compression test to make sure the motor itself is in decent shape. While the plugs are out - replace them and throw a set of plug wires on for good measure. Pull the Distributor cap - and check to see if the rotor looks OK along with the inside of the distributor terminals. If there is even a question about them being good - replace the cap / Rotor.

Personally - I'd pull the battery and take it along with me to the parts place and have it tested. I'd hope it's newer than 7 years - but I highly doubt that a 7 year old battery is going to be able to cut it.

Now - You have new fuel in the tank - correct. Try starting it up - if it's still running like crap - you probably have a fuel system / EFI problem - but double check that the spark being delivered to the plugs is good, and that the timing is somewhere near correct. I'd also check to see that the alternator is charging - you need to see more than 13.5 volts (probably over 14 - especially in this weather) with the car running over 1,500 RPM.

If everything above checks out OK - it's time to get into the fuel injection system. If the fuel filter wasn't replaced - replace it. Then check fuel pressure (preferably while the engine is trying to run) - the pump could easily be unhappy.

If all is good with the fuel supply - then the only area left is the fuel injection system. When you pulled the plugs - how did they look - sooty ??? wet with fuel ??? If they were wet - you may have leaking injectors - pull them off the engine and see if they leak when the fuel pump is running. Do they all seem to fire as you crank ??? I would also try to get a vacuum reading at as close to idle as the car will do - you said that there is evidence that seals were replaced - so it would be nice to know if you have a major vacuum leak... (which is guaranteed to cause the engine to run badly)

Once you get to this point - then it's time to see if the various EFI sensors are doing their jobs. Yes, it's quite possible that it's related to idle airflow, and the IAC - but that shouldn't impact how the car runs at say 2,500 RPM.... But - if you get to this point - you're now into the realm of changing electrical parts - and as you probably know - once you buy them - you own them - so I'd check the other stuff first....

GOOD LUCK !!!

vader86

Well I'd need to know more to diagnose, but I'd start with a few things if a car hadn't been running.

- Check fuel pressure at the nipple on the rail, note how it behaves on startup, idle, open the throttle by hand, shutdown and post shutdown.
- Check adequate spark by pulling a plug wire (but they do have testers)
- Check for stored codes/SES lights with the paperclip trick

One of those 3 things should point you where to go if its a serious problem. Then
- Replace cap/coil/rotor/plugs/wires and be sure to check firing order. Set the timing to 6* after you get her running, although 8 is fine.
- Check vac leaks with a spray bottle of soapy water, a big leak will make it run terrible but it should run.
- Replace the fuel filter (no matter what at this point).
- A bad MAF 'should' set a code if its this bad, but unplugging it will show you, if it runs a lot better, then the MAF itself is bad. If its only startup-related, then I would discount it being a MAF. You should replace both relays if you replace the MAF sensor itself. Check that fuel/spark first.
- If you have a laptop and OBD1 cable that you can stick DataMaster on, then that is a better, more-advanced tool to see whats up. You can also buy handheld scanners from AutoZone that will tell you whats up at this point too. But, start with fuel/spark and not these.

skyhawk50

thanks for the info

skyhawk50

fuel filter repaced, I got a spark checker and am going to OHM the injectors as well. Injectors are yellow.....Bosch???, OBD 1 scanners almost non-existent around here


thanks for your response

skyhawk50

It was a cold ride home Wednesday. Note: passenger window up( fixed that within first 1/2 hr) Top dry rotted but a new-in-box top came with the car ( guess I’ll have to learn how to install tops next ). Wheels aren’t my style, but I’ll deal with them at a later date. Tires are brand new.

billschroeder5842

Nice vert. You are well on your way to sorting it out.

Polo Vert

You won't have any trouble selling those wheels.

hcbph

I use an Innova 3140 on my 86 Vette and my ODB II vehicles to read and reset codes. Works well for me.

VikingTrad3r

when u check timing build or buy a piston stop and verify tdc mark. when i hear backfire ...can u tell us if it us intake or exhaust backfiring

skyhawk50

Ok, finally braved the cold garage. Checked fuel pressure, turn key on, immediately jumps to 45, then drops to zero. Whats next, FPR diaphragm or is fuel pump related ? PO said fuel pump was replaced.

tunedport85inject

My experience with FP issue:
Some guys here say C4's hold their fuel pressure about 20 minutes steady at 42 psi.My 85 didn't ever hold her 38 psi (in 85' they had a lower pressure and bigger injectors) .Time ago i did my deep investigation on this.I was assuming the fact she had to hold 38 psi.I started from basic test.Primed several time the rail and she never held but immediately pressure dropped to 10 psi and held there for some minutes.I pinched the return line with a clamp near the filling cup and she was steady at 38 after priming.This test was made to be sure no injectors were leaking.I guessed it was a broken diaphragm,so i changed my FPR .No way ,simply the pressure was not steady.Now assuming no injectors leaking,no broken FPr,why she doesn't hold its pressure?i went to the final assumption that the fuel line is designed to work with a given amount of pressure and flow,while engine is firing the amount of pressure is steady because the pump is constantly working pumping gas into the line,the FPR regulates the operating pressure and any amount of un-injected gas simply returns to the tank.So when you stop the engine and the pump quits the pressure drops...

Purple92

If she holds the 45 psi while running - then fuel supply ISN'T the problem - cross that one off and keep looking....

skyhawk50

I can’t even keep it running. Key on, not started....pressure goes up to 45 and immediatel drops to 0.....

Backfiring appears to be in the intake"...

billschroeder5842

Yikes, you may have an injector leak or a really bad FPR.

skyhawk50

Would a leaky injector cause a rapid leak down ?

VikingTrad3r

do this to isolate the leakdown source.

get a friend. grab two sets of pliers and wrap tape around teeth on pliers. black tape works best.

remove the fuel hatch and the rubber splash tray.

one of you stand at back with pliers in hand ready to sqeeze the fuel sending and return line.

one guy in fromt seat turns key on (nor car on)


wait for pump to do its cycle. then the guyat back clamps both send and return line. i use vice grips. not too tight. dont want to damage lines.

now watch the pressure. does it bleed off???

if yes, gently pull the vac line off the fpr and see if there is fuel wet or smell. if yes, u have a leaking fpr. if not, if its dry or no smell, your injectors are leaking or your fuel is leaking from elsewhere. if you dont see fuel pooling anywhere then your injector(s) are leaking.

do not replace with multecs. call jon at fuel injector connection and order whatever he recommends.

lets us know how that test turns out and well guide u from there.

skyhawk50

I’ll give that a try.

Car has Bosch injectors now, installed by PO. I’ve bought injectors from FIC in the past for my other C4’s

aklim

Does it just read and reset codes or will it do a data stream? For the former, a paper clip will work and to reset, disconnect battery. I am having trouble finding a true scanner other than the SnapOn Brick or a couple others. They are no longer supported for a hand held. Will try the ALDL Droid at some point.