Help Needed - Engine Miss Is Gradually Getting Worse!

[RoyalViking]

I have a 1989 that has 106000 miles. I noticed an engine miss about a month ago. Since that time I had driven about 500 miles and it had gotten worse over time. Mileage was ok and it seemed to come and go. Last weekend I drove it 1200 miles. At the start of the trip I was a little concerned as the miss got worse about 200 miles into the trip and then it calmed down a bit as I continued to drive. I had noticed that during parts of my trip it would come and go again. On the final 150 miles it seemed to get better. The miss never went away all together. Mileage the first half of the trip was 26.8 and the return trip was 24.5 mpg (actual miles driven vs gallons used).

I was going to drive it to work yesterday and it seemed really bad. I drove it about 3 miles and parked it at a friend's house. When I drove it home after work it seemed to be even worse. In the driveway I ran it up to 3000 rpm in park and it dropped to 2000 rpm as i held my foot at the position where it when first at 3000 rpm.

Tonight I started it up and it ran ok. As it warmed up it began to miss again. I had the engine running in the driveway with the underhood lights off looking for bad wires or any arcing. The check engine light is not on. My scan tool has bit the dust so I can't use it to check for any codes.

Has anyone had this problem?

 

[hotshotzny]

did you check the obvious plugs/wires etc
how old are the wires....
i know on my 82 pulling the plugs is not an easy task at all

also on my car the control module needed to be replaced to straigten out my car

im sure someone alot more knowledgeable will chime in

 

[sstearns2]

You might have a fuel injector that's on it's way out. You can check them by removing the little connectors on each injector and checking the resistance across the two pins. It should be 16 ohms.

My 90 with 40K miles had one at 14 ohms and one at 12 ohms and it idles at lot smoother with the new injectors, but the new injectors are a much better design too.

Scott

 

[CSS996]

Fuel Pump/ Filter?

 

[Blown C4]

HEI coil ?

 

[SPANISHVETTS]

Need more info.
Lots of things make the L98 miss. Do the basic trouble shooting first.
I had a miss at operating temp caused by the RTV on the intake leaking coolant. Somewhere here at CAC there is a 3 page about it.
Is the engine ¨stock¨ ? Several of us have had lots of problems with the plug boots and plugs overheating on highly modified engines. I have had a few plugs crack the ceramic insulator where it enters the base.

In 25 years of vetting it has always been a basic failure. i.e., I have never had an ECM or any other hi-tech failure.

keep us posted

 

[RoyalViking]

Thanks for the feedback. I've been working on another vehicle and have not had the chance to even look at anything except for a cracked wire the other night.

- The engine is stock.

- The question about the injectors has me wondering. I had to replace several PAK-CON connectors in the fuse box recently. I am wondering if one of the crimps I made is the issue. There are three fuses to the ECM and two of them provide power to the injectors.

- I'l check the other things tomorrow if the weather cooperates.

 

[Hib Halverson]

With that mileage on it....have you done a compression or leakage test. If so, what were the results?

Also, since some of the discussion is about injectors, have you run the fuel pressure tests in the factory service manual?

 

[RoyalViking]

I finally got a chance to look at the car.

Fuel pressure is ok. The pressure was at 43 PSI when the key is in run. With the engine running it was steady at 39 PSI. I put 10" vaccum on the pressure regulator and it dropped to 40.5 PSI (engine running, vacuum port plugged an vaccum pump on regulator).

The engine was surging at idle.

Pulled all but plug wires # 1 and 3 individually while running. Wires are ok with what I could check (things were getting hot).

Here's something interesting. I checked the resistance of the injectors. Cylinder 3 was 5.7 ohms and 5 was 9.1 ohms! Cylinder 4 was 7.1 ohms. Looks like I need to replace them.

Does anyone know how may lbs per hour the stock injectors flow? Any recomendations on what I should use?

 

[sstearns2]

Sounds like the injectors are your problem. I used the design III rebuilt injectors here, 22 lbs/hr....

http://fuelinjectorconnection.com/shop/index.php?_a=viewCat&catId=61

Price is good and the car runs great. It's not too bad of a job to do yourself.

Scott

 

[RoyalViking]

Sounds like the injectors are your problem. I used the design III rebuilt injectors here, 22 lbs/hr....

http://fuelinjectorconnection.com/shop/index.php?_a=viewCat&catId=61

Price is good and the car runs great. It's not too bad of a job to do yourself.

Scott

Thanks for the link. Thats a lot less than I expected to pay.

I noticed they have 24 lbs/hr. Is there any advantage to using them over the 22 lbs/hr? I had the intake off before to replace the leaking intake valley gaskets (i.e. silicone gasket). This should be a lot easier than the entire manifold.

Does any one know if it is worth changing ovver to the adjustable fuel pressure regulator?

 

[RoyalViking]

Thanks for the link. Thats a lot less than I expected to pay.

I noticed they have 24 lbs/hr. Is there any advantage to using them over the 22 lbs/hr? I had the intake off before to replace the leaking intake valley gaskets (i.e. silicone gasket). This should be a lot easier than the entire manifold.

Does any one know if it is worth changing ovver to the adjustable fuel pressure regulator?

I finally got to looking into the question I had about the 24 lb/hr injectors.

On FIC's web site they recommend using a performance chip if going to the 24 lbs/hr. It seems that the late 85 thru 93 had the 22 lb/hr injectors. I began to add up the cost of the performance chip, the 24 lb/hr injectors, and the adjustable pressure regulator cap. I decided that to spend the additional money at this time was more than I could justify. If the car was running I would be using the money for doors seals and other items related to the body. This morning I called up their tech line and spoke with John. He answered my remaining questions. I have to say the guy loves his business and it was a pleasure to talk to him.

I ordered the 22lb/hr injectors this afternoon. I'll post again after the injectors are installed.

 

[Toms007]

Jon is one of the nicest people you'll ever do business with. I bought my injectors from him back in early June. I installed them and had a couple of issue/questions, Jon called me to see what he could do to help. He then modified a set of Injectors and wanted me to try them out, sent out the new ones and then called back a couple of days later to make sure they were working as he said, and now I understand that the modification he made to them is done with every set like that, that he sells.

I am currently having my own issues with rough running/bucking etc. Jon read my posts about it and has called to discuss the issue, he has assured me it is not the injectors but told me in an email that he is sending me a new set out "...to set your mind at ease..."

You do not find this kind of service in today's world. 2 thumbs up for FIC.

 

[RoyalViking]

I got the new injectors. We've had a lot of rain lately (I guess the drought is over) and I am looking for a time when I can do this all at once. I have to do the job in the driveway and don't want to leave the intake apart overnight if I can't finish it in time. When I was talking to Jon he said it would probably take about 6 hours.

I'll post again after I get the new ones installed.

 

[RoyalViking]

I got the new injectors. We've had a lot of rain lately (I guess the drought is over) and I am looking for a time when I can do this all at once. I have to do the job in the driveway and don't want to leave the intake apart overnight if I can't finish it in time. When I was talking to Jon he said it would probably take about 6 hours.

I'll post again after I get the new ones installed.

Well I worked on it last Saturday for about 6 hours straight. When you read this you have to understand that I had to work on this out doors and had to get the intake closed up in the same day. I removed the injectors and installing the new ones. I got the runners installed and then realized I could not get the plenum on. So I loosened them again and got the plenum on. After all of that I realized I had not checked to see if I had any fuel leaks. It turned out that I had a leak. A fairly good one as I could hear the fuel spraying from inside the car. I worked on it again Sunday afternoon. I found that one of the top injector o-rings had worked it's way down and was not seated in the groove (the Gen III do not use the clip to retain the injectors in the fuel rail). I was able to loosen the fuel rail bolts and lift it so that I could get the injector o-ring in place. That took about an hour and a half to get the fuel back in place.

The car didn't start the first try. I drove it a couple miles and could tell a slight difference. When I was on a bumpy road it came to life. I punched it in first and it took off like it used to. After getting back on a smooth surface again it ran the same as before. I think the new injectors solved one problem. The bigger issue still remains. I have not had a chance to look at the car since then.

I am still suspicious of the fuse box connections. I had to replace some of them as they began to loose tension or actually crack and fail. Could the TPS cause this?

 

[RoyalViking]

Ok, I've ruled out the connections at the fuse box, they're all good, and there are no vacuum leaks. The TPS has a dead spot at about 3/4 throttle (I almost never go there).

Here are the present symptoms. Engine may take two or more tries to get it started, rpms are very low at first, it idles like it has a hotter cam, the engine seems to be running very rich, when I am on a bumpy road it will run great.

I am open to suggestions...

 

[Hib Halverson]

Is the service engine light on or has it ever been on?
Does the service engine light flash during bulb check?
Do you own a scan tester?
If the oxygen sensors have not been replaced in the last 50,000 miles, I'd install new ones.
I don't know if an 89 has a TPS adjustment, but if the Service Manual calls for it, you need to adjust it per the manual using a DMM.

When you say, "on a bumpy road it will run great" tells me that you may have a wiring and connection problem somewhere, ie: when the wires/connections are wiggling and bouncing around they make contact.

 

[TWISTERUP]

Ok, I've ruled out the connections at the fuse box, they're all good, and there are no vacuum leaks. The TPS has a dead spot at about 3/4 throttle (I almost never go there).

Here are the present symptoms. Engine may take two or more tries to get it started, rpms are very low at first, it idles like it has a hotter cam, the engine seems to be running very rich, when I am on a bumpy road it will run great.

I am open to suggestions...

From your description (bumpy roads) it sounds to me also like a electrical connection/poor wiring rubbing/touching at times. HOWEVER water in the fuel can also cause some of your symptoms. I'd get a sample in a clear glass jar and check it.If it is in fact running rich, of course water wouldn't cause that. It may be worth a check none the less>

 

[RoyalViking]

I found the loose connection today. It's a shame I waited so long to take another look. I had the dash apart and went over the fuse box again. Since I couldn't remove the new connectors without damaging it (I know there is a special too for removing them) I decided I would check for loose connections with the engine running. I worked my way around the fuse box to try and repeat the same change as on the bumpy road. I went to the engine and decided that if I could disconnect a fuel injector I could determine which fuse circuit was faulty. What I found was one of the connections to a fuel injector was not pushed all of the way in and as I experienced on a bumpy road it was making contact.

I drove it yesterday about 5 miles and it was fine. I drove it today another 15 miles and everything seemed fine. Gas mileage has improved as well.

A couple things remain. It is still slow to start and it has an occaisional missfire while driving.

 

[RoyalViking]

As it turns out things were better but not by much. The mpg went from 16 to 21 mpg. I was not getting the 27 mpg plus on the highway anymore. I was able to look at it last Saturday and found the source of the miss. It was cylinder #6. I pulled the wire with no change in rpm, I then pulled the injector with the same result. I could tell the injector was working as I could feel it pulse like the others. Ok, I pulled the plug and it was black except the tip of the plug. I swapped it with the plug in cylinder 3 and then started it up again. I was wondering if the plug was fouled. As it turns out the platnum plugs hold up well. The plug was fine. I decided to buy a new set of wires. I got a chance to put them on after work and started the car up. It ran without any missfire. I took it out for a drive tonight. It looks like the driveability problem is fixed.

I guess this is a good lesson for me. Each time I would get something fixed I would have to start over again with the trouble shooting steps in the factory manual. Things that I thought were ok must have been masked until the bigger problem was fixed.

Thanks everyone for your help. I would not have known where to look for the injectors and would have spent far more than I needed to. Hopefully this is the end of this thread unless someone else wants to pick it up again.