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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 08-23-2014, 02:22 AM   #1
Quarterhorse636
 
Join Date: Aug 2014
Vehicle: 1990 Ford Mustang
Location: Missouri
Posts: 11
Default 1990 preigntion missing problem

Hi Everyone im new to this whole forum deal so bear with me. Im more than capable of fixing the problem but I need to know what the problem is before I can do that. Hopefully you guys can help me out. I bought a almost crisp almost stock 1990 mustang gt with a 306 , aftermarket 19lb injecters, aftermarket e303 cam, ac shorty headers, offroad hpiped< 1.6 roller rockers, cai, underdrive pulleys and supposedly ported e7 heads ( took the headers of and found casting marks. I haven't seen the intake side). My problem is when I get up to go to work at the last second ill go out and start my car itll start rev up then die. Ill start it back up itll run a little longer than die. Try it a again then itll run on its own but it will surge slightly till it gets a little warm. When I take off and put a load on the engine it will kind of bog down and most of the time backfire through the intake once or twice, but that will go away once it gets completely warm. its my understanding that backfiring through the intake is called pre-ignition or pinging. I can get around this pre-ignition problem by revving the engine high enough while taking off so that it wont do that. like I said it will go away once it gets warm and it will drive just fine until I get caught at a stoplight and sit for roughly 3 minutes and go to take off it doesn't really bog down but it seems like its missing very noticeably. Heres what I don't get.. when its starts missing and I turn the car off and start it again while rolling it will fix itself until I get caught at the next stoplight then it may or may not happen again. this is a daily problem


now heres what ive done to battle this problem. checked my vacuum, its at 10-12in. new aic, new ect, cleaned egr, new tps set at .99vdc, new o2's. ive had the time set at every reasonable degree and it runs different but not better. ive done a compression test and the cylinders were between 160psi and 180 psi. fuel pressure is at 40psi consistently and rises when I step on the gas. car dies when i unplug the maf. did the carb cleaner spray tick on the meeting surfaces but i didn't find anything.

I forgot to mention that I do have trouble codes 41 and 91.from what ive read that means the car is running lean on both sides.

In my case when an engine is bored out and now there is more volume to be filled does that mean I should get bigger injectors? is 10- 12 in of vacuum seem to low? maybe my pip sensor or something in the distributor isn't working properly.


Please help me before i have to pay somebody to do it for me. after 7 years of driving and ten different piece of crap cars ive never had to take one to a shop. Id like to keep it that way.
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Old 08-23-2014, 05:32 AM   #2
dawson1112
5th Gear Member
 
Join Date: Jul 2012
Vehicle: 1990 lx hatch 5.0
Location: ohio
Posts: 2,676
Default

Id like to know a few things here.

What is your timing set at? What rpm does the car idle at, cold and once it warms up?

Set your timing at the stock 10btdc , insure that the outer ring on the balancer has not spun. The balancers on these cars are known to spin the outer ring if the rubber is cracked or oil soaked. Bring #1 cylinder to TDC compression stroke, and verify timing pointer is at 0.
:::NOTE::: You must have the engine at full operating temp, remove the spout, and use a timing light to set proper timing. 10-14 btdc ,, start at 10 then advance a little at a time until pinging is heard , back it off a little till pinging stops.

10-12hg vacuum reading seems a bit low to me even for that e303. My 90 lx had a 306 with the e303 cam and vacuum pulled to about 12-14hg. Your fuel pressure seems a bit high at idle, it should be 34-36psi at idle. Ive never heard of anyone or any reason to put after market 19lb injectors in a car unless they were replacements. What color are they?

A few things I would do here to start off with.

1 Clean the MAF sensor with some maf cleaner spray.
2 start looking at the vacuum lines under the intake, the rubber takes a lot of heat stress over the years, and it tends to become brittle and crack.
3 make sure your not getting any unmetered air entering after the MAF .. ie check all your intake tube connections for any leaks.

4 Make sure you have no exhaust leaks before the 02 sensors .. ie leaking header gaskets, or flange connections. It will suck air in and cause lean readings.

5 Check and clean all grounds, make sure the ground from the rear of the heads to the body is connected.

6 clean/replace the air filter. The after market reusable filters like the ones that come with most CAIs are the number 1 most neglected items on the intake system. They are oil coated and should be cleaned a couple times a year.

The computer looks a few things to determine how long the injector pulse should be. Incoming air flow , coolant temp, oxygen in the exhaust being the main data.

Any air entering the system after the MAF is unmetered giving false readings from the MAF.

The oil coated filters can also contribute to a dirty MAF if it was over coated in oil. This will also contribute to false MAF readings.

Plugged or very dirty air filters do not let the proper amount of air flow over the MAF .

Sometimes clocking the MAF 180 degrees on the intake tube can help a slightly modded engine get a better reading of incoming air.

As for the back firing.... Is it actually backfiring or is it pinging... There is a very distinct difference. Backfiring is heard as popping, , while ignition knock is heard as a distinct rattle almost like a diesel engine.

These procedures should give you a starting point in locating your issue, report back after you complete these steps.
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Old 08-24-2014, 11:05 PM   #3
Quarterhorse636
 
Join Date: Aug 2014
Vehicle: 1990 Ford Mustang
Location: Missouri
Posts: 11
Default

hey thanks for your response. i did most of what you said so let me tell you what i did.

my timing is set at 12 degrees. but ive had it set all over the place just to see what it will do. each time I change it will run different but not better. 12 degrees just seems to be the best magic number.

when I start her up the rpm will peak at about 1300 or so then drop then die. start it again itll do the same thing but it might catch itself before it actually dies but most likely it will die within about 30 seconds of surging. then itll run like crap till it warms up then I shut it off and the problem will go away till I get caught at a light and just let I idle. then itll start stumbling and backfire upon takeoff. but if I turn the car off at the red light and start it when its green it wont do that.

i cant tell if the outer ring on the balancer has spun. i did notice that the rubber is dryrotted and has started to crack. i set the balacer at zero and checked to see if the #1 piston was at tdc and it was.

i cant say that iver ever heard an engine ping so i don't know that that sound like. ive been told it sounds like marbles rattling in a coffee can or something like that. if i advance the timing to much i don't hear anything like that.. then it will just die.

i was wrong about the vacumm pressure. when the engine is warm and i start it up with the vaccumm gauge hooked up it will sit around 15hg for about a minute then drop down to 10-12 or even lower than that. like 8-10hg! then it will creep up 10-12hg. when i gun the throttle the pressure will drop down close to 0 then shoot up to 20-30hg. is it supposed to do that?

i checked my fuel pressure again. it was at 38 with the vacumm on and 41 or so with the vacumm off

the aftermarket 19lb injectors were just replacements i think. they are black in color but they say 19lb/hr on the injector top.


some things you asked i had already done just forgot to mention it in my first post.

1.i already cleaned the maf with maf cleaner before but i did it again just to be sure
2.i found some rubber vaccum lines that run around the upper intake that were cracked because of age and heat i suppose but i hooked my mighty vac up to one end and put my finger over the other and they were not leaking. i replaced them anyways.
3.i checked the rubber couplers for my cai and sprayed car cleaner on them theyre not leaking
4.before i had and exhaust leak at the header flange to downpipe fixed that and retourqued all the bolts.
5.i haven't cleaned the grounds yet i did check the big ground start and it was okay.
6. i didn't replace or clean the airfilter


before i thought pinging and a backfire through the intake was the same thing. but no it is not pinging. it is backfireing. it sounds like "bloop" but really loud.

i did some other things to. i replaced all the gaskets from the upper intake to the throttle body. i was planning on doing the lower intake but this is my only vehicle right now so i want going to chance something breaking or having to wait on a part because i wouldn't have a ride to work. anyways when i took the upper off i was curious to see how tight the lower was. my Haynes book said it had to be tourqued at 25 ft lbs i got at least 3/4 of a turn before the ratchet clicked, so they weren't very tight. then i cleaned the old gasket off of everything and put it back together..... doing all this didn't help.


im real curious about this vaccum thing why do you think it starts at 15hg stays then drops down? i think this is the cause of my stoplight dilemma and possibly other things. possibly like something that runs off the vaccum opens up just enough to let the pressure drop and not allow it to fix itself.

what octane should i be running? i was told mustangs rolled out of the factory running 93 octane so that's what ive been putting in it but i did some research and found that it should use 89 or 91 with about 10-12 degrees advanced. is this true. this may also be the cause of my backfiring problem.

ugh.......... thank you so much for your time man
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Old 08-25-2014, 08:48 AM   #4
dawson1112
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Join Date: Jul 2012
Vehicle: 1990 lx hatch 5.0
Location: ohio
Posts: 2,676
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Does your car still have an egr valve on it?

Possibly the egr valve has a lot of carbon deposits and it letting some exhaust back in at idle. . .
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Old 08-25-2014, 11:39 AM   #5
Quarterhorse636
 
Join Date: Aug 2014
Vehicle: 1990 Ford Mustang
Location: Missouri
Posts: 11
Default

Yea it still has one. But I took it off to clean it before. It wasn't even that dirty to begin with but I cleaned it anyways. I tested it yesterday to see if it was even working. On a forum they said to hook up a vacuum pump to the port on the egr and give it 5 inches of vacumm at idle then it should either stumble or die which it did.
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Old 08-25-2014, 11:39 AM
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